A GaN-based semiconductor light-emitting element includes a first GaN-based compound semiconductor layer of n-conductivity type, an active layer, a second GaN-based compound semiconductor layer of p-conductivity type, a first electrode electrically connected to the first GaN-based compound semiconductor layer, a second electrode electrically connected to the second GaN-based compound semiconductor layer, an impurity diffusion-preventing layer composed of an undoped GaN-based compound semiconductor, the impurity diffusion-preventing layer preventing a p-type impurity from diffusing into the active layer, and a laminated structure or a third GaN-based compound semiconductor layer of p-conductivity type. The impurity diffusion-preventing layer and the laminated structure or the third GaN-based compound semiconductor layer of p-conductivity type are disposed, between the active layer and the second GaN-based compound semiconductor layer, in that order from the active layer side.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority to Japanese Patent Application JP 2008-066595 filed in the Japanese Patent Office on Mar. 14, 2008, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present application relates to a GaN-based semiconductor light-emitting element, a light-emitting element assembly and a light-emitting apparatus each having such a GaN-based semiconductor light-emitting element, a method of manufacturing such a GaN-based semiconductor light-emitting element according to an embodiment, a method of driving such a GaN-based semiconductor light-emitting element, and an image display apparatus having such a GaN-based semiconductor light-emitting element.

In a light-emitting element (GaN-based semiconductor light-emitting element) having an active layer composed of a gallium nitride (GaN)-based compound semiconductor, the band-gap energy can be controlled by changing the compound crystal composition or thickness of the active layer, and thus it is possible to realize a light emission wavelength in a wide range from ultraviolet to infrared. GaN-based semiconductor light-emitting elements emitting light of various colors have already been commercially available and used in a variety of applications, such as image display apparatuses, illumination apparatuses, testing apparatuses, and sterilizing light sources. Furthermore, blue-violet semiconductor lasers and light-emitting diodes (LEDs) have also been developed and used as writing/reading pickups of large-capacity optical disks.

In general, a GaN-based semiconductor light-emitting element has a structure in which a first GaN-based compound semiconductor layer of n-conductivity type, an active layer, and a second GaN-based compound semiconductor layer of p-conductivity type are sequentially stacked.

In the related art, for example, a second GaN-based compound semiconductor layer having a superlattice structure including a Mg-doped AlGaN layer and a Mg-doped GaN layer is formed above an active layer, the superlattice structure being subjected to uniform doping or modulation doping. Formation of such a second GaN-based compound semiconductor layer having a superlattice structure has been reported to have an effect of increasing the hole concentration (for example, refer to K. Kumakura and N. Kobayashi, Jpn. J. Appl. Phys. vol. 38 (1999) pp. L1012; P. Kozodoy et al., Appl. Phys. Lett. 75, 2444 (1999); and P. Kozodoy et al., Appl. Phys. Lett. 74, 3681 (1999)). In this technique, high hole concentrations are obtained two-dimensionally by the piezoelectric effect due to strain, and it has been reported that by optimizing the period of the superlattice structure, the same effect (i.e., decrease in series resistance) can also be obtained with respect to the conduction in the thickness direction of the second GaN-based compound semiconductor layer.

SUMMARY

However, in the superlattice structure described above, the effect of increasing the hole concentration in the active layer is not sufficient, and a technique for achieving higher light emission efficiency is strongly desired.

It is desirable to provide a GaN-based semiconductor light-emitting element having a structure capable of increasing light emission efficiency, a light-emitting element assembly and a light-emitting apparatus each having such a GaN-based semiconductor light-emitting element, a method of manufacturing such a GaN-based semiconductor light-emitting element according to an embodiment, a method of driving such a GaN-based semiconductor light-emitting element, and an image display apparatus having such a GaN-based semiconductor light-emitting element.

A GaN-based semiconductor light-emitting element according to a first embodiment or a second embodiment of the present application includes (A) a first GaN-based compound semiconductor layer of n-conductivity type, (B) an active layer, (C) a second GaN-based compound semiconductor layer of p-conductivity type, (D) a first electrode electrically connected to the first GaN-based compound semiconductor layer, and (E) a second electrode electrically connected to the second GaN-based compound semiconductor layer, and the GaN-based semiconductor light-emitting element includes, between the active layer and the second GaN-based compound semiconductor layer, disposed in that order from the active layer side, (F) an impurity diffusion-preventing layer composed of an undoped GaN-based compound semiconductor, the impurity diffusion-preventing layer preventing a p-type impurity from diffusing into the active layer, and, according to the first embodiment, (G) a laminated structure, or according to the second embodiment (G) a third GaN-based compound semiconductor layer of p-conductivity type.

In the GaN-based semiconductor light-emitting element according to the first embodiment, the laminated structure includes at least one laminate unit in which a GaN-based compound semiconductor layer of p-conductivity type and an undoped GaN-based compound semiconductor layer are stacked in that order from the active layer side.

In the GaN-based semiconductor light-emitting element according to the second embodiment, at least one undoped GaN-based compound semiconductor layer is disposed on a side, closer to the second GaN-based compound semiconductor layer, of the third GaN-based compound semiconductor layer.

A light-emitting element assembly according to a first embodiment includes the GaN-based semiconductor light-emitting element according to the first embodiment, the GaN-based semiconductor light-emitting element being disposed on a supporting member. Furthermore, a light-emitting element assembly according to a second embodiment includes the GaN-based semiconductor light-emitting element according to the second embodiment, the GaN-based semiconductor light-emitting element being disposed on a supporting member.

A light-emitting apparatus according to a first embodiment or a second embodiment includes (a) a GaN-based semiconductor light-emitting element and (b) a color conversion material which is excited by emitted light from the GaN-based semiconductor light-emitting element to emit light with a different wavelength from that of the emitted light. In the light-emitting apparatus according to the first embodiment, the GaN-based semiconductor light-emitting element is constituted by the GaN-based semiconductor light-emitting element according to the first embodiment, In the light-emitting apparatus according to the second embodiment, the GaN-based semiconductor light-emitting element is constituted by the GaN-based semiconductor light-emitting element according to the second embodiment.

An image display apparatus according to a first embodiment includes a GaN-based semiconductor light-emitting element for displaying an image, and the GaN-based semiconductor light-emitting element is constituted by the GaN-based semiconductor light-emitting element according to the first embodiment. Furthermore, an image display apparatus according to a second embodiment a GaN-based semiconductor light-emitting element for displaying an image, and the GaN-based semiconductor light-emitting element is constituted by the GaN-based semiconductor light-emitting element according to the second embodiment.

When the image display apparatus according to the first embodiment or the second embodiment is a color image display apparatus, the image display apparatus includes at least a first light-emitting element which emits blue light, a second light-emitting element which emits green light, and a third light-emitting element which emits red light. The GaN-based semiconductor light-emitting element according to the first embodiment or the second embodiment should constitute at least one (one type) of the first light-emitting element, the second light-emitting element, and the third light-emitting element.

In the GaN-based semiconductor light-emitting element according to the first embodiment, the GaN-based semiconductor light-emitting element in the light-emitting element assembly according to the first embodiment, the GaN-based semiconductor light-emitting element in the light-emitting apparatus according to the first embodiment, or the GaN-based semiconductor light-emitting element in the image display apparatus according to the first embodiment (hereinafter generically referred to as the “first GaN-based semiconductor light-emitting element”), the GaN-based compound semiconductor layer of p-conductivity type and the undoped GaN-based compound semiconductor layer constituting the laminate unit may have the same composition. Furthermore, in the GaN-based semiconductor light-emitting element according to the second embodiment, the GaN-based semiconductor light-emitting element in the light-emitting element assembly according to the second embodiment, the GaN-based semiconductor light-emitting element in the light-emitting apparatus according to the second embodiment, or the GaN-based semiconductor light-emitting element in the image display apparatus according to the second embodiment (hereinafter generically referred to as the “second GaN-based semiconductor light-emitting element”), the third GaN-based compound semiconductor layer of p-conductivity type and the undoped GaN-based compound semiconductor layer disposed on the third GaN-based compound semiconductor layer may have the same composition.

In the first GaN-based semiconductor light-emitting element, the undoped GaN-based compound semiconductor layer constituting the laminate unit may include a GaN-based compound semiconductor layer, the composition of which contains indium. Furthermore, in the second GaN-based semiconductor light-emitting element, the undoped GaN-based compound semiconductor layer disposed on the third GaN-based compound semiconductor layer may include a GaN-based compound semiconductor layer, the composition of which contains indium.

In the first GaN-based semiconductor light-emitting element, the undoped GaN-based compound semiconductor layer constituting the laminate unit may have a three-layer structure including a first layer having the same composition as the GaN-based compound semiconductor layer of p-conductivity type constituting the laminate unit, a second layer having the composition which is the same as the first layer and which further contains indium, and a third layer having the same composition as the first layer. In such a case, the undoped GaN-based compound semiconductor layer constituting the laminate unit may have a three-layer structure including the first layer composed of undoped GaN, the second layer composed of undoped InxGa(1-x)N (wherein 0<x≦0.3), and the third layer composed of undoped GaN. Furthermore, the active layer may include an InyGa(1-y)N layer, wherein x≦y.

In the second GaN-based semiconductor light-emitting element, the undoped GaN-based compound semiconductor layer disposed on the third GaN-based compound semiconductor layer may have a three-layer structure including a first layer having the same composition as the third GaN-based compound semiconductor layer of p-conductivity type, a second layer having the composition which is the same as the first layer and which further contains indium, and a third layer having the same composition as the first layer. In such a case, the undoped GaN-based compound semiconductor layer disposed on the third GaN-based compound semiconductor layer may have a three-layer structure including the first layer composed of undoped GaN, the second layer composed of undoped InxGa(1-x)N (wherein 0<x≦0.3), and the third layer composed of undoped GaN. Furthermore, the active layer may include an InyGa(1-y)N layer, wherein x≦y.

In each of the first GaN-based semiconductor light-emitting elements including the preferred embodiments and structures described above, preferably, the laminated structure includes one to ten laminate units. In each of the second GaN-based semiconductor light-emitting elements including the preferred embodiments and structures described above, preferably, one to ten undoped GaN-based compound semiconductor layers are disposed on the third GaN-based compound semiconductor layer.

In each of the first GaN-based semiconductor light-emitting elements including the preferred embodiments and structures described above, preferably, the GaN-based compound semiconductor layer of p-conductivity type constituting the laminate unit has a p-type impurity concentration of preferably 1×1018/cm3to 4×1020/cm3, and more preferably 1×1019/cm3to 2×1020/cm3. In each of the second GaN-based semiconductor light-emitting elements including the preferred embodiments and structures described above, the third GaN-based compound semiconductor layer has a p-type impurity concentration of preferably 1×1018/cm3to 4×1020/cm3, and more preferably 1×1019/cm3to 2×1020/cm3.

Furthermore, in each of the first GaN-based semiconductor light-emitting elements including the preferred embodiments and structures described above, the thickness of the GaN-based compound semiconductor layer of p-conductivity type constituting the laminate unit may be in the range of two-atomic-layer thickness to 50 nm, the thickness of the undoped GaN-based compound semiconductor layer constituting the laminate unit may be in the range of two-atomic-layer thickness to 50 nm, and the thickness of the laminated structure may be in the range of 5 nm to 200 nm. In each of the second GaN-based semiconductor light-emitting elements including the preferred embodiments and structures described above, the thickness of the undoped GaN-based compound semiconductor layer disposed on the third GaN-based compound semiconductor layer may be in the range of two-atomic-layer thickness to 50 nm, and the thickness of the third GaN-based compound semiconductor layer may be in the range of 5 nm to 200 nm.

Furthermore, in each of the first GaN-based semiconductor light-emitting elements or the second GaN-based semiconductor light-emitting elements including the preferred embodiments and structures described above (hereinafter may be generically referred to as the “GaN-based semiconductor light-emitting element or the like”), the density of a current applied to the active layer (operating current density) is preferably 50 amperes/cm2or more, more preferably 100 amperes/cm2or more, and still more preferably 200 amperes/cm2or more.

In the GaN-based semiconductor light-emitting element or the like including the preferred embodiments and structures described above, the area of the active layer is preferably 1×10−12m2to 1×10−8m2, and more preferably 1×10−11m2to 1×10−9m2.

In the GaN-based semiconductor light-emitting element or the like including the preferred embodiments and structures described above, the thickness of the GaN-based semiconductor light-emitting element is preferably 1×10−7m to 1×10−5m, and more preferably 1×10−6m to 1×10−5m.

There is provided a method of manufacturing a GaN-based semiconductor light-emitting element according to a first embodiment, the method being a method of manufacturing any of the GaN-based semiconductor light-emitting elements including the preferred embodiments or structures described above according to the first embodiment, in which the undoped GaN-based compound semiconductor layer constituting the laminate unit includes a GaN-based compound semiconductor layer, the composition of which contains indium, and the active layer includes a GaN-based compound semiconductor layer, the composition of which contains indium, the method including sequentially forming the first GaN-based compound semiconductor layer, the active layer, the impurity diffusion-preventing layer, the laminated structure, and the second GaN-based compound semiconductor layer, in which the GaN-based compound semiconductor layer, the composition of which contains indium, in the undoped GaN-based compound semiconductor layer constituting the laminate unit is formed at a higher temperature than the temperature at which the GaN-based compound semiconductor layer, the composition of which contains indium, in the active layer is formed.

There is provided a method of manufacturing a GaN-based semiconductor light-emitting element according to a second embodiment, the method being a method of manufacturing any of the GaN-based semiconductor light-emitting elements including the preferred embodiments or structures described above according to the second embodiment, in which the undoped GaN-based compound semiconductor layer disposed on the third GaN-based compound semiconductor layer includes a GaN-based compound semiconductor layer, the composition of which contains indium, and the active layer includes a GaN-based compound semiconductor layer, the composition of which contains indium, the method including sequentially forming the first GaN-based compound semiconductor layer, the active layer, the impurity diffusion-preventing layer, the third GaN-based compound semiconductor layer, and the second GaN-based compound semiconductor layer, in which the GaN-based compound semiconductor layer, the composition of which contains indium, in the undoped GaN-based compound semiconductor layer disposed on the third GaN-based compound semiconductor layer is formed at a higher temperature than the temperature at which the GaN-based compound semiconductor layer, the composition of which contains indium, in the active layer is formed.

There is provided a method of driving a GaN-based semiconductor light-emitting element according to a first embodiment, the method being a method of driving any of the GaN-based semiconductor light-emitting elements including the preferred embodiments or structures described above according to the first embodiment, the method including applying a current with a current density (operating current density) of 50 amperes/cm2or more, preferably 100 amperes/cm2or more, more preferably 200 amperes/cm2or more to the active layer.

There is provided a method of driving a GaN-based semiconductor light-emitting element according to a second embodiment, the method being a method of driving any of the GaN-based semiconductor light-emitting elements including the preferred embodiments or structures described above according to the second embodiment, the method including applying a current with a current density (operating current density) of 50 amperes/cm2or more, preferably 100 amperes/cm2or more, more preferably 200 amperes/cm2or more to the active layer.

Note that the operating current density of the GaN-based semiconductor light-emitting element is defined as the value obtained by dividing the operating current value by the area (area of junction region) of the active layer. That is, commercially available GaN-based semiconductor light-emitting elements have various package forms, and also the size of the GaN-based semiconductor light-emitting elements varies depending on the application or the amount of light. Furthermore, the standard driving current (operating current) varies depending on the size of the GaN-based semiconductor light-emitting elements. Thus, it is difficult to directly compare current dependency of properties between elements. In the present application, for generalization purposes, instead of the driving current value itself, the operating current density (unit of measure: ampere/cm2), which is obtained by dividing the driving current value by the area (area of junction region) of the active layer, is expressed.

In each of the GaN-based semiconductor light-emitting element, the light-emitting element assembly, the light-emitting apparatus, the method of manufacturing the GaN-based semiconductor light-emitting element, the method of driving the GaN-based semiconductor light-emitting element, and the image display apparatus including the preferred embodiments or structures according to the first embodiment or the second embodiment, examples of the first GaN-based compound semiconductor layer, the second GaN-based compound, semiconductor layer, and the impurity diffusion-preventing layer include a GaN layer, an AlGaN layer, an InGaN layer, and an AlInGaN layer. Furthermore, as desired, these compound semiconductor layers may contain boron (B) atoms, thallium (Tl) atoms, arsenic (As) atoms, phosphors (P) atoms, and antimony (Sb) atoms. The active layer may have, for example, an InGaN/GaN single quantum well (QW) structure or an InGaN/GaN multiple quantum well (MQW) structure.

In the method of manufacturing the GaN-based semiconductor light-emitting element according to the first embodiment or the second embodiment, the first GaN-based compound semiconductor layer, etc. are sequentially formed on a light-emitting element-forming substrate. Examples of the light-emitting element-forming substrate that can be used include a sapphire substrate, a GaAs substrate, a GaN substrate, a SiC substrate, an alumina substrate, a ZnS substrate, a ZnO substrate, an AlN substrate, a LiMgO substrate, a LiGaO2substrate, a MgAl2O4substrate, an InP substrate, a Si substrate, and these substrates having an underlying layer or a buffer layer on the surface (principal surface) thereof. In the GaN-based semiconductor light-emitting element according to the first embodiment or the second embodiment, the GaN-based semiconductor light-emitting element in the light-emitting apparatus according to the first embodiment or the second embodiment, and the GaN-based semiconductor light-emitting element in the image display apparatus according to the first embodiment or the second embodiment, there are a case where the light-emitting element-forming substrate is allowed to remain and a case where the light-emitting element-forming substrate is removed finally. Note that in the latter case, the GaN-based semiconductor light-emitting element is provided on the supporting member.

Examples of the supporting member in the light-emitting element assembly according to the first embodiment or the second embodiment include, in addition to the examples of the light-emitting element-forming substrate described above, a glass substrate, a metal substrate, a metal sheet, an alloy substrate, an alloy sheet, a ceramic substrate, a ceramic sheet, a semiconductor substrate, a plastic substrate, a plastic sheet, and a plastic film. Examples of the plastic film include a polyethersulfone (PES) film, a polyethylene naphthalate (PEN) film, a polyimide (PI) film, and a polyethylene terephthalate (PET) film. Other examples of the supporting member include a glass substrate to which any of the various films described above is bonded, and a glass substrate having a polyimide resin layer, an acrylic resin layer, a polystyrene resin layer, or a silicone rubber layer thereon. Furthermore, the glass substrate may be replaced with a metal substrate or a plastic substrate. Alternatively, an insulating film may be formed on the surface of these substrates. Examples of the material constituting the insulating film include inorganic insulating materials, such as silicon oxide-based materials, silicon nitrides (SiNY), and metal oxide high dielectric insulating films; and organic insulating materials, such as polymethyl methacrylate (PMMA), polyvinylphenol (PVP), and polyvinyl alcohol (PVA). These materials may be used in combination. Examples of the silicon oxide-based materials include silicon oxides (SiOX), silicon oxynitride (SiON), spin on glass (SOG), and low dielectric constant SiOX-based materials (such as polyaryl ethers, cycloperfluorocarbon polymers, benzocyclobutene, cyclic fluorocarbon resins, polytetrafluoroethylene, fluorinated aryl ethers, fluorinated polyimides, amorphous carbon, and organic SOG). Examples of a method of forming the insulating film include PVD methods, CVD methods, a spin coating method, printing methods, coating methods, an immersion method, a casting method, and a spray method.

In the light-emitting apparatuses including the preferred embodiments or structures described above according to the first embodiment or the second embodiment (hereinafter may be generically referred to as the “light-emitting apparatus”), examples of emitted light from the GaN-based semiconductor light-emitting element include visible light, ultraviolet light, and a combination of visible light and ultraviolet light.

In the light-emitting apparatus, a structure may be employed in which the light emitted from the GaN-based semiconductor light-emitting element is blue light, and the light emitted from the color conversion material is at least one type of light selected from the group consisting of yellow light, green light, and red light, and a structure may be employed in which the light emitted from the GaN-based semiconductor light-emitting element and the light emitted from the color conversion material (e.g., yellow; red and green; yellow and red; or green, yellow, and red) are mixed to emit white light. Specific examples of the color conversion material which is excited by the blue light emitted from the GaN-based semiconductor light-emitting element to emit red light include red light-emitting fluorescent particles, and, more specifically, (ME:Eu)S [wherein ME represents at least one atom selected from the group consisting of Ca, Sr, and Ba; hereinafter the same], (M:Sm)x(Si,Al)12(O,N)16[wherein M represents at least one atom selected from the group consisting of Li, Mg, and Ca; hereinafter the same], ME2Si5N8:Eu, (Ca:Eu)SiN2, and (Ca:Eu)AlSiN3. Specific examples of the color conversion material which is excited by the blue light emitted from the GaN-based semiconductor light-emitting element to emit green light include green light-emitting fluorescent particles, and, more specifically, (ME:Eu)Ga2S4, (M:RE)x(Si,Al)12(O,N)16[wherein RE represents Tb and Yb], (M:Tb)x(Si,Al)12(O,N)16, (M:Yb)x(Si,Al)12(O,N)16, and Si6-ZAlZOZN8-Z:Eu. Specific examples of the color conversion material which is excited by the blue light emitted from the GaN-based semiconductor light-emitting element to emit yellow light include yellow light-emitting fluorescent particles, and, more specifically, YAG (yttrium-aluminum-garnet)-based fluorescent particles. These color conversion materials may be used alone or as a mixture of two or more. When a mixture of two or more color conversion materials is used, light of a color other than yellow, green, and red can be emitted from the color conversion material mixture. Specifically, a structure may be employed in which cyan light is emitted. In such a case, a mixture of green light-emitting fluorescent particles (e.g., LaPO4:Ce,Tb, BaMgAl10O17:Eu,Mn, Zn2SiO4:Mn, MgAl11O19:Ce,Tb, Y2SiO5:Ce,Tb, or MgAl11O19:CE,Tb,Mn) and blue light-emitting fluorescent particles (e.g., BaMgAl10O17:Eu, BaMg2Al16O27:Eu, Sr2P2O7:Eu, Sr5(PO4)3Cl:Eu, (Sr,Ca,Ba,Mg)5(PO4)3Cl:Eu, or CaWO4, CaWO4:Pb) may be used.

Furthermore, specific examples of the color conversion material which is excited by the ultraviolet light emitted from the GaN-based semiconductor light-emitting element to emit red light include red light-emitting fluorescent particles, and, more specifically, Y2O3:Eu, YVO4:Eu, Y(P,V)O4:Eu, 3.5MgO.0.5MgF2.Ge2:Mn, CaSiO3:Pb,Mn, Mg6AsO11:Mn, (Sr,Mg)3(PO4)3:Sn, La2O2S:Eu, and Y2O2S:Eu. Specific examples of the color conversion material which is excited by the ultraviolet light emitted from the GaN-based semiconductor light-emitting element to emit green light include green light-emitting fluorescent particles, and, more specifically, LaPO4:Ce,Tb, BaMgAl10O17:Eu,Mn, Zn2SiO4:Mn, MgAl11O19:Ce,Tb, Y2SiO5:Ce,Tb, MgAl11O19:CE,Tb,Mn, and Si6-ZAlZOZN8-Z:Eu. Specific examples of the color conversion material which is excited by the ultraviolet light emitted from the GaN-based semiconductor light-emitting element to emit blue light include blue light-emitting fluorescent particles, and, more specifically, BaMgAl10O17:Eu, BaMg2Al16O27:Eu, Sr2P2O7:Eu, Sr5(PO4)3Cl:Eu, (Sr,Ca,Ba,Mg)5(PO4)3Cl:Eu, CaWO4, and CaWO4:Pb. Specific examples of the color conversion material which is excited by the ultraviolet light emitted from the GaN-based semiconductor light-emitting element to emit yellow light include yellow light-emitting fluorescent particles, and, more specifically, YAG-based fluorescent particles. These color conversion materials may be used alone or as a mixture of two or more. When a mixture of two or more color conversion materials is used, light of a color other than yellow, green, and red can be emitted from the color conversion material mixture. Specifically, a structure may be employed in which cyan light is emitted. In such a case, a mixture of green light-emitting fluorescent particles and blue light-emitting fluorescent particles may be used.

The color conversion material is not limited to fluorescent particles. Other examples of the color conversion material include luminescent particles composed of an indirect transition-type silicon material having a quantum well structure, such as a two-dimensional quantum well structure, a one-dimensional quantum well structure (quantum wire), or a zero-dimensional quantum well structure (quantum dot), in which the carrier wave function is localized so that carriers can be efficiently converted into light as in the direct transition-type material, thus using a quantum effect. It has been reported that rare earth atoms added to a semiconductor material sharply emit light by intra-shell transition, and luminescent particles using such a technique can also be used.

Examples of the image display apparatuses including the preferred embodiments and structures described above according to the first embodiment or the second embodiment (hereinafter may be generically referred to as the “image display apparatus”) include image display apparatuses having the structures described below. Unless otherwise specified, the number of GaN-based semiconductor light-emitting elements constituting an image display apparatus or a light-emitting element panel may be determined on the basis of the specifications of the image display apparatus. Furthermore, a light valve may be further provided on the basis of the specifications of the image display apparatus.

(1) Image Display Apparatus Having a First Structure

A passive matrix-type or active matrix-type, direct-view-type image display apparatus including (α) a light-emitting element panel having GaN-based semiconductor light-emitting elements arranged in a two-dimensional matrix, in which the emission state of each of the GaN-based semiconductor light-emitting elements is directly visually observed by controlling the emission/non-emission state of each GaN-based semiconductor light-emitting element to display an image.

(2) Image Display Apparatus Having a Second Structure

A passive matrix-type or active matrix-type, projection-type image display apparatus including (α) a light-emitting element panel having GaN-based semiconductor light-emitting elements arranged in a two-dimensional matrix, in which the emission/non-emission state of each GaN-based semiconductor light-emitting element is controlled to display an image by projection on a screen.

(3) Image Display Apparatus Having a Third Structure

A color image display apparatus (direct-view-type or projection-type) including (α) a red light-emitting element panel having red light-emitting semiconductor light-emitting elements (e.g., AlGaInP-based semiconductor light-emitting elements or GaN-based semiconductor light-emitting elements; hereinafter the same) arranged in a two-dimensional matrix; (β) a green light-emitting element panel having green light-emitting GaN-based semiconductor light-emitting elements arranged in a two-dimensional matrix; (γ) a blue light-emitting element panel having blue light-emitting GaN-based semiconductor light-emitting elements arranged in a two-dimensional matrix; and (δ) a device which collects the light emitted from the red light-emitting element panel, the green light-emitting element panel, and the blue light-emitting element panel in an optical path (e.g., a dichroic prism; hereinafter the same), in which the emission/non-emission state of each of the red light-emitting semiconductor light-emitting elements, the green light-emitting GaN-based semiconductor light-emitting elements, and the blue light-emitting GaN-based semiconductor light-emitting elements is controlled.

(4) Image Display Apparatus Having a Fourth Structure

An image display apparatus (direct-view-type or projection-type) including (α) a GaN-based semiconductor light-emitting element and (β) a light transmission controller [e.g., a liquid crystal display device, a digital micromirror device (DMD), or a liquid crystal on silicon (LCOS) device; hereinafter the same] which is a light valve for controlling transmission/non-transmission of light emitted from the GaN-based semiconductor light-emitting element, in which transmission/non-transmission of light emitted from the GaN-based semiconductor light-emitting element is controlled by the light transmission controller to display an image. The number of GaN-based semiconductor light-emitting elements may be determined on the basis of the specifications of the image display apparatus, and may be one or two or more. Furthermore, examples of a device (light-guiding member) that guides light emitted from the GaN-based semiconductor light-emitting element to the light transmission controller include an optical guide member, a microlens array, a mirror, a reflector plate, and a condensing lens.

(5) Image Display Apparatus Having a Fifth Structure

An image display apparatus (direct-view-type or projection-type) including (α) a light-emitting element panel having GaN-based semiconductor light-emitting elements arranged in a two-dimensional matrix and (β) a light transmission controller (light valve) which controls transmission/non-transmission of light emitted from the GaN-based semiconductor light-emitting elements, in which transmission/non-transmission of light emitted from the GaN-based semiconductor light-emitting elements is controlled by the light transmission controller to display an image.

(6) Image Display Apparatus Having a Sixth Structure

A color image display apparatus (direct-view-type or projection-type) including (α) a red light-emitting element panel having red light-emitting semiconductor light-emitting elements arranged in a two-dimensional matrix, and a red light transmission controller (light valve) which controls transmission/non-transmission of light emitted from the red light-emitting element panel; (β) a green light-emitting element panel having green light-emitting GaN-based semiconductor light-emitting elements arranged in a two-dimensional matrix, and a green light transmission controller (light valve) which controls transmission/non-transmission of light emitted from the green light-emitting element panel; (γ) a blue light-emitting element panel having blue light-emitting GaN-based semiconductor light-emitting elements arranged in a two-dimensional matrix, and a blue light transmission controller (light valve) which controls transmission/non-transmission of light emitted from the blue light-emitting element panel; and (δ) a device which collects the light transmitted through the red light transmission controller, the green light transmission controller, and the blue light transmission controller in an optical path, in which the transmission/non-transmission of light emitted from each of the light-emitting element panels is controlled by the corresponding light transmission controller to display an image.

(7) Image Display Apparatus Having a Seventh Structure

A field-sequential color image display apparatus (direct-view-type or projection-type) including (α) a red light-emitting semiconductor light-emitting element; (β) a green light-emitting GaN-based semiconductor light-emitting element; (γ) a blue light-emitting GaN-based semiconductor light-emitting element; (δ) a device which collects the light emitted from the red light-emitting semiconductor light-emitting element, the green light-emitting GaN-based semiconductor light-emitting element, and the blue light-emitting GaN-based semiconductor light-emitting element in an optical path; and (∈) a light transmission controller (light valve) which controls transmission/non-transmission of light emitted from the device which collects the light in the optical path, in which the transmission/non-transmission of light emitted from each of the light-emitting elements is controlled by the light transmission controller to display an image.

(8) Image Display Apparatus Having an Eighth Structure

A field-sequential color image display apparatus (direct-view-type or projection-type) including (α) a red light-emitting element panel having red light-emitting semiconductor light-emitting elements arranged in a two-dimensional matrix; (β) a green light-emitting element panel having green light-emitting GaN-based semiconductor light-emitting elements arranged in a two-dimensional matrix; (γ) a blue light-emitting element panel having blue light-emitting GaN-based semiconductor light-emitting elements arranged in a two-dimensional matrix; (δ) a device which collects the light emitted from the red light-emitting element panel, the green light-emitting element panel, and the blue light-emitting element panel in an optical path; and (∈) a light transmission controller (light valve) which controls transmission/non-transmission of light emitted from the device which collects the light in the optical path, in which the transmission/non-transmission of light emitted from each of the light-emitting element panels is controlled by the light transmission controller to display an image.

(9) Image Display Apparatus Having a Ninth Structure

A passive matrix-type or active matrix-type, direct-view-type color image display apparatus including a first light-emitting element, a second light-emitting element, and a third light-emitting element, in which the emission state of each of the light-emitting elements is directly visually observed by controlling the emission/non-emission state of each light-emitting element to display an image.

(10) Image Display Apparatus Having a Tenth Structure

A passive matrix-type or active matrix-type, projection-type color image display apparatus including a first light-emitting element, a second light-emitting element, and a third light-emitting element, in which the emission/non-emission state of each light-emitting element is controlled to display an image by projection on a screen.

(11) Image Display Apparatus Having an Eleventh Structure

A field-sequential color image display apparatus (direct-view-type or projection-type) including light-emitting element units arranged in a two-dimensional matrix, and a light transmission controller (light valve) which controls transmission/non-transmission of light emitted from the light-emitting element units, in which the emission/non-emission state of each of a first light-emitting element, a second light-emitting element, and a third light-emitting element in each light-emitting element unit is controlled by time sharing, and the transmission/non-transmission of light emitted from the first light-emitting element, the second light-emitting element, and the third light-emitting element is controlled by the light transmission controller to display an image.

In the method of manufacturing the GaN-based semiconductor light-emitting element according to the first embodiment or the second embodiment, preferably, the relationship TMAX<1,350−0.75λ is satisfied, and more preferably, the relationship TMAX<1,250−0.75λ is satisfied in order to prevent the occurrence of thermal damage to the active layer, wherein TMAX(° C.) is the maximum growth temperature in the crystal growth of each of the undoped GaN-based compound semiconductor layers in the laminate unit or on and in the third GaN-based compound semiconductor layer, and λ is the light emission wavelength of the active layer. Examples of the method for forming the various layers composed of a GaN-based compound include metal-organic chemical vapor deposition (MOCVD), MBE, and hydride vapor deposition in which a halogen contributes to transportation or reaction.

In MOCVD, as the organogallium source gas, trimethylgallium (TMG) gas or triethylgallium (TEG) gas may be used, and as the nitrogen source gas, ammonia gas or hydrazine gas may be used. In the formation of a GaN-based compound semiconductor layer of n-conductivity type, for example, silicon (Si) may be added as an n-type impurity (n-type dopant). In the formation of a GaN-based compound semiconductor layer of p-conductivity type, for example, magnesium (Mg) may be added as a p-type impurity (p-type dopant). Furthermore, when the GaN-based compound semiconductor layer includes aluminum (Al) or indium (In) as a constituent atom, trimethylaluminum (TMA) gas may be used as an Al source and trimethylindium (TMI) gas may be used as an In source. Furthermore, monosilane gas (SiH4gas) may be used as an Si source, and cyclopentadienylmagnesium gas, methylcyclopentadienylmagnesium, or bis(cyclopentadienyl)magnesium (Cp2Mg) may be used as a Mg source. Furthermore, besides Si, examples of the n-type impurity (n-type dopant) include Ge, Se, Sn, C, and Ti. Besides Mg, examples of the p-type impurity (p-type dopant) include Zn, Cd, Be, Ca, Ba, and O.

The second electrode electrically connected to the second GaN-based compound semiconductor layer of p-conductivity type (or the second electrode disposed on the contact layer) preferably has a single-layer structure or a multilayer structure including at least one metal selected from the group consisting of palladium (Pd), platinum (Pt), nickel (Ni), aluminum (Al), titanium (Ti), gold (Au), and silver (Ag). Alternatively, a transparent conductive material such as indium tin oxide (ITO) may be used. In particular, silver (Ag), Ag/Ni, or Ag/Ni/Pt that can reflect light with high efficiency is preferably used. On the other hand, the first electrode electrically connected to the first GaN-based compound semiconductor layer of n-conductivity type preferably has a single-layer structure or a multilayer structure including at least one metal selected from the group consisting of gold (Au), silver (Ag), palladium (Pd), aluminum (Al), titanium (Ti), tungsten (W), copper (Cu), zinc (Zn), tin (Sn), and indium (In). Examples thereof include Ti/Au, Ti/Al, and Ti/Pt/Au. The first electrode and the second electrode may be formed by physical vapor deposition (PVD), such as vacuum deposition or sputtering. The first electrode is electrically connected to the first GaN-based compound semiconductor layer, and the first electrode may be disposed on the first GaN-based compound semiconductor layer or may be connected to the first GaN-based compound semiconductor layer via a conductive material layer. Similarly, the second electrode is electrically connected to the second GaN-based compound semiconductor layer, and the second electrode may be disposed on the second GaN-based compound semiconductor layer or may be connected to the second GaN-based compound semiconductor layer via a conductive material layer.

A pad electrode may be provided on each of the first electrode and the second electrode in order to achieve electrical connection to an external electrode or circuit. The pad electrode preferably has a single-layer structure or a multilayer structure including at least one metal selected from the group consisting of titanium (Ti), aluminum (Al), platinum (Pt), gold (Au), and nickel (Ni). The pad electrode may have a multilayer structure, such as Ti/Pt/Au or Ti/Au.

The quantity of light emission (luminance) of the GaN-based semiconductor light-emitting element can be controlled by controlling the pulse width of the driving current, the pulse density of the driving current, or by combination of both, and in addition to this, by the peak current value of the driving current. The reason for this is that a change in the peak current value of the driving current only slightly affects the light emission wavelength of the GaN-based semiconductor light-emitting element.

Specifically, an example will be described in which, in a GaN-based semiconductor light-emitting element, I0represents the peak current value of the driving current for a certain light emission wavelength λ0, P0represents the pulse width of the driving current, and TOPrepresents one-operation period of the GaN-based semiconductor light-emitting element or the like or one-operation period in the method of driving the GaN-based semiconductor light-emitting element according to the first embodiment or the second embodiment. In such a case, (1) by controlling (adjusting) the peak current value I0of the driving current, the quantity of light emission (luminance) from the GaN-based semiconductor light-emitting element can be controlled; and (2) by controlling the pulse width P0of the driving current (pulse width control of driving current), the quantity of light emission (brightness or luminance) from the a GaN-based semiconductor light-emitting element can be controlled; and/or (3) by controlling the number of pulses (pulse density) with the pulse width P0in the one-operation period TOPof the GaN-based semiconductor light-emitting element (pulse density control of driving current), the quantity of light emission (brightness or luminance) from the GaN-based semiconductor light-emitting element can be controlled.

The above-described control of the quantity of light emission from the GaN-based semiconductor light-emitting element can be achieved by a driving circuit for the GaN-based semiconductor light-emitting element, the driving circuit including (a) a pulsed driving current supply unit which supplies pulsed driving current to the GaN-based semiconductor light-emitting element, (b) a pulsed driving current setting unit which sets the pulse width and pulse density of the driving current, and (c) a unit which sets the peak current value.

In each of the GaN-based semiconductor light-emitting element, the light-emitting element assembly, the light-emitting apparatus, the method of manufacturing the GaN-based semiconductor light-emitting element, the method of driving the GaN-based semiconductor light-emitting element, and the image display apparatus including the preferred embodiments or structures according to the first embodiment or the second embodiment, the GaN-based semiconductor light-emitting element may have a face-up structure (i.e., a structure in which light generated by the active layer is emitted from the second GaN-based compound semiconductor layer) or a flip-chip structure (i.e., a structure in which light generated by the active layer is emitted from the first GaN-based compound semiconductor layer). Furthermore, the GaN-based semiconductor light-emitting element may be designed to be, for example, a shell-shaped element or a surface-mount-type element.

Specific examples of the GaN-based semiconductor light-emitting element include a light-emitting diode (LED) and a semiconductor laser (LD). The structure and configuration of the GaN-based semiconductor light-emitting element are not particularly limited as long as the multilayer structure thereof has a light-emitting diode structure or a laser structure. Furthermore, besides the above-described light-emitting apparatuses including GaN-based semiconductor light-emitting elements and color conversion materials and image display apparatuses (direct-view-type or projection-type), the GaN-based semiconductor light-emitting element according to the first embodiment or the second embodiment can be applied to planar light-source devices (backlights); liquid crystal display device assemblies including color liquid crystal display device assemblies; light sources for variable color illumination; displays; lamp fittings and lights in vehicles, such as automobiles, electric trains, ships, and aircrafts (e.g., headlights, taillights, high mounted stop lights, small lights, turn signal lamps, fog lights, interior lamps, meter-panel lights, light sources provided in various buttons, destination lamps, emergency lights, and emergency exit guide lights); various lamp fittings and lights in buildings (e.g., outdoor lights, interior lights, lighting equipment, emergency lights, and emergency exit guide lights); street lights; various indicating lamp fittings of traffic signals, advertising displays, machines, and apparatuses; lightings and lighting parts in tunnels, underground passages, and the like; special illuminations in various testing apparatuses such as biological microscopes; sterilizers using light; deodorizing sterilizers combined with photocatalysts; exposure devices for photographs and semiconductor lithography; and devices for modulating light to transmit information through spaces, optical fibers, or waveguides.

When a GaN-based semiconductor light-emitting element according to the first embodiment or the second embodiment is applied to a planar light-source device, as described above, the light source includes a first light-emitting element which emits blue light, a second light-emitting element which emits green Slight, and a third light-emitting element which emits red light, and the GaN-based semiconductor light-emitting element according to the first embodiment or the second embodiment can constitute at least one (one type) of the first light-emitting element, the second light-emitting element, and the third light-emitting element. The present application is not limited thereto, The light source in the planar light-source device may be constituted by one or two or more light-emitting apparatuses according to any embodiment. The number of each of the first light-emitting element, the second light-emitting element, and the third light-emitting element may be one or two or more. The planar light-source device may be one of two types of planar light-source devices (backlights): a direct-type planar light-source device, for example, disclosed in Japanese Unexamined Utility Model Registration Application Publication No. 63-187120 or Japanese Unexamined Patent Application Publication No. 2002-277870, and an edge light type (also referred to as “side light type”) planar light-source device, for example, disclosed in Japanese Unexamined Patent Application Publication No. 2002-131552. The number of GaN-based semiconductor light-emitting elements is essentially arbitrary, and may be determined on the basis of the specifications of the planar light-source device. The first light-emitting element, the second light-emitting element, and the third light-emitting element are arranged so as to face a liquid crystal display device, and a diffuser plate, an optical functional sheet group including a diffuser sheet, a prism sheet, and a polarization conversion sheet, and a reflection sheet are placed between the liquid crystal display device and each of the first light-emitting element, the second light-emitting element, and the third light-emitting element.

The GaN-based semiconductor light-emitting element according to the first embodiment or the second embodiment of the present application includes a laminated structure including at least one laminate unit in which a GaN-based compound semiconductor layer of p-conductivity type and an undoped GaN-based compound semiconductor layer are stacked, or includes a third GaN-based compound semiconductor layer on which at least one undoped GaN-based compound semiconductor layer is disposed at a side closer to the second GaN-based compound semiconductor layer. Consequently, it is possible to achieve higher light emission efficiency in the GaN-based semiconductor light-emitting element.

DETAILED DESCRIPTION

The present application will be described based on examples with reference to the drawings according to an embodiment.

Example 1 relates to GaN-based semiconductor light-emitting elements according to the first embodiment and the second embodiment, and the methods of driving the GaN-based semiconductor light-emitting elements according to the first embodiment and the second embodiment.FIG. 1Ais a schematic partial cross-sectional view of a GaN-based semiconductor light-emitting element in Example 1, andFIG. 1Bshows a structure including a first GaN-based compound semiconductor layer, an active layer, a laminated structure (a third GaN-based compound semiconductor layer), a second GaN-based compound semiconductor layer, and the like.

A GaN-based semiconductor light-emitting element (more specifically, light-emitting diode)1in Example 1 includes (A) a first GaN-based compound semiconductor layer21of n-conductivity type, (B) an active layer23, (C) a second GaN-based compound semiconductor layer22of p-conductivity type, (D) a first electrode31electrically connected to the first GaN-based compound semiconductor layer21, and (E) a second electrode32electrically connected to the second GaN-based compound semiconductor layer22.

The GaN-based semiconductor light-emitting element1further includes, between the active layer23and the second GaN-based compound semiconductor layer22, disposed in that order from the active layer side, (F) an impurity diffusion-preventing layer24composed of an undoped GaN-based compound semiconductor, the impurity diffusion-preventing layer24preventing a p-type impurity from diffusing into the active layer23, and (G) a laminated structure40according to the first embodiment, or (G) a third GaN-based compound semiconductor layer50of p-conductivity type according to the second embodiment.

According to the first embodiment, the laminated structure40includes at least one laminate unit41in which a GaN-based compound semiconductor layer42of p-conductivity type and an undoped GaN-based compound semiconductor layer43are stacked in that order from the active layer side. Specifically, the laminated structure40includes two laminate units41in Example 1.

According to the second embodiment, at least one undoped GaN-based compound semiconductor layer53is disposed on a side, closer to the second GaN-based compound semiconductor layer22, of the third GaN-based compound semiconductor layer50. In Example 1, two undoped GaN-based compound semiconductor layers53are provided.

In Example 1, the GaN-based compound semiconductor layer42of p-conductivity type and the undoped GaN-based compound semiconductor layer43constituting the laminate unit41have the same composition, i.e., GaN. Meanwhile, the third GaN-based compound semiconductor layer50of p-conductivity type and the undoped GaN-based compound semiconductor layer53disposed on the third GaN-based compound semiconductor layer50have the same composition, i.e., GaN. The p-type impurity concentration of the GaN-based compound semiconductor layer42of p-conductivity type constituting the laminate unit41or the p-type impurity concentration of the third GaN-based compound semiconductor layer50is 1×1018/cm3to 4×1020/cm3, and specifically 5×1019/cm3.

Furthermore, the thickness of the GaN-based compound semiconductor layer42of p-conductivity type constituting the laminate unit41is 5 nm, the thickness of the undoped GaN-based compound semiconductor layer43constituting the laminate unit41(or the thickness of the undoped GaN-based compound semiconductor layer53disposed on the third GaN-based compound semiconductor layer50) is 13 nm, and the thickness of the laminated structure40(or the thickness of the third GaN-based compound semiconductor layer50) is 36 nm (=18 nm×2). Furthermore, the area of the active layer23is 4×10−10m2and the thickness of the GaN-based semiconductor light-emitting element1is 5×10−6m. In the drawing, reference numeral10represents a light-emitting element-forming substrate, and reference numeral11represents an underlying layer including a buffer layer and an undoped GaN layer disposed thereon.

In the GaN-based semiconductor light-emitting element1in Example 1, a current with a current density (operating current density) of 50 amperes/cm2or more, preferably 100 amperes/cm2or more, and more preferably 200 amperes/cm2or more is applied to the active layer23.

A method of manufacturing a GaN-based semiconductor light-emitting element in Example 1 will be described below.

First, a sapphire substrate whose principal surface is the C plane is used as the light-emitting element-forming substrate10. The light-emitting element-forming substrate10is subjected to cleaning at a substrate temperature of 1,050° C. for 10 minutes in a carrier gas composed of hydrogen, and then the substrate temperature is decreased to 500° C., A buffer layer composed of low-temperature GaN with a thickness of 30 nm is formed by crystal growth on the light-emitting element-forming substrate10by means of MOCVD in which trimethylgallium (TMG) gas as a gallium source is supplied while ammonia gas as a nitrogen source is being supplied, and then the supply of TMG gas is halted. After the substrate temperature is increased to 1,020° C., the supply of TMG gas is restarted. Thus, an undoped GaN layer with a thickness of 1 μM is formed by crystal growth on the buffer layer. Thereby, an underlying layer11is obtained. Subsequently, supply of monosilane gas (SiH4gas) as a silicon source is started. Thus, a first GaN-based compound semiconductor layer21of n-conductivity type composed of Si-doped GaN (GaN:Si) with a thickness of 3 μm is formed by crystal growth on the undoped GaN layer constituting the underlying layer11. The doping concentration is about 5×1018/cm3.

Then, the supply of TMG gas and SiH4gas is halted, the carrier gas is switched from hydrogen gas to nitrogen gas, and the substrate temperature is decreased to 750° C. Triethylgallium (TEG) gas is used as a Ga source and trimethylindium (TMI) gas is used as an In source. By switching the valve, these gases are supplied. Thereby, an active layer23having a multiple quantum well structure including well layers composed INGaN and barrier layers composed of GaN is formed. The substrate temperature may be fluctuated during the crystal growth. The compositional proportion of In in the well layer is, for example, 0.23, which corresponds to a light emission wavelength λ of 520 mm. The compositional proportion of In in the well layer can be determined according to the desired light emission wavelength. Here, the number of well layers is five, and the number of barrier layers is four.

After the formation of the active layer23having the multiple quantum well structure is completed, an impurity diffusion-preventing layer24composed of undoped GaN with a thickness of 5 nm is grown while increasing the substrate temperature to 800° C.

Subsequently, with the substrate temperature being maintained at 800° C., supply of bis(cyclopentadienyl)magnesium (Cp2Mg) gas as a Mg source is started. Thus, a GaN-based compound semiconductor layer42of p-conductivity type (specifically, Mg-doped GaN layer42) is grown with a thickness of 5 nm. Next, in the state in which the supply of Cp2Mg gas is halted, an undoped GaN-based compound semiconductor layer43(specifically, undoped GaN layer43) is grown with a thickness of 13 nm. In such a manner, the Mg-doped GaN layer42with a thickness of 5 nm and the undoped GaN layer43with a thickness of 13 nm are grown twice repeatedly. The doping concentration of Mg is about 5×1019/cm3. Thereby, a laminated structure40including at least one laminate unit41in which the GaN-based compound semiconductor layer42of p-conductivity type and the undoped GaN-based compound semiconductor layer43are stacked in that order from the active layer side can be obtained. Alternatively, a third GaN-based compound semiconductor layer50having at least one undoped GaN-based compound semiconductor layer53(undoped GaN layer53) on the side closer to the second GaN-based compound semiconductor layer22can be obtained.

Then, the supply of TEG gas and Cp2Mg gas is halted, the carrier gas is switched from nitrogen to hydrogen, and the substrate temperature is increased to 850° C. By starting supply of TMG gas and Cp2Mg gas, a second GaN-based compound semiconductor layer22composed of Mg-doped GaN (GaN:Mg) with a thickness of 100 nm is formed by crystal growth. The doping concentration is about 5×1019/cm3. Then, a contact layer (not shown) composed of InGaN is formed by crystal growth. The supply of TMG gas and Cp2Mg gas is stopped, and the substrate temperature is decreased. The supply of ammonia gas is stopped at the substrate temperature of 600° C., and the substrate temperature is decreased to room temperature to complete the crystal growth.

With respect to the substrate temperature TMAXafter the growth of the active layer23, the relationship TMAX<1,350−0.75λ (° C.) is satisfied, and preferably, the relationship TMAX<1,250−0.75λ (° C.) is satisfied. By using such a substrate temperature TMAXafter the growth of the active layer23, as described in Japanese Unexamined Patent Application Publication No. 2002-319702, the active layer23can be prevented from being thermally degraded.

After the crystal growth is completed, annealing treatment is performed at 800° C. in a nitrogen gas atmosphere for ten minutes to activate the p-type impurity (p-type dopant).

Subsequently, as in the ordinary LED wafer process and chip formation process, a protective film (not shown) is formed, a second electrode32and a first electrode31are formed by photolithography, etching, and metal vapor deposition, and chips are formed by dicing, followed by resin molding and packaging. Thus, a GaN-based semiconductor light-emitting element1in Example 1 (e.g., any of various types of light-emitting diodes, such as shell-shaped light-emitting diodes and surface-mount-type light-emitting diodes) can be fabricated.

In Comparative Example 1, a GaN-based semiconductor light-emitting element is fabricated in which a second GaN-based compound semiconductor layer22is directly formed on an impurity diffusion-preventing layer24without forming a laminated structure40(or a third GaN-based compound semiconductor layer50including an undoped GaN-based compound semiconductor layer53) (refer toFIG. 26).

With respect to the GaN-based semiconductor light-emitting element in each of Example 1 or Example 2, which will be described below, and Comparative Example 1, for evaluation purposes, using lithography and etching, the first GaN-based compound semiconductor layer21was partially exposed, a second electrode32composed of Ag/Ni was formed on the second GaN-based compound semiconductor layer22, and a first electrode31composed of Ti/Al was formed on the first GaN-based compound semiconductor layer21. Probe needles were brought into contact with the first electrode and the second electrode. A driving current was applied to the light-emitting element, and light emitted from the back surface of the light-emitting element-forming substrate10was detected.FIG. 2is a conceptual diagram showing the evaluation process, in which the laminated structure40, etc. are omitted.

FIG. 4Ais a graph showing the relationship between the operating current density (ampere/cm2) and the light emission efficiency (watt/ampere) in each of Example 1 and Comparative Example 1. As is evident from the graph, Example 1 has a light emission efficiency at the same operating current density that is certainly increased compared with Comparative Example 1. The increase in the light emission efficiency can be confirmed over the entire range of operating current densities from a common LED operating current density (30 amperes/cm2) to a high operating current density (300 amperes/cm2). The light emission wavelength is 520 nm in each of Example 1 and Comparative Example 1, or Example 2 described below.

As described above, by forming the laminated structure40having the undoped GaN-based compound semiconductor layer43(or the third GaN-based compound semiconductor layer50including the undoped GaN-based compound semiconductor layer53) between the active layer23and the second GaN-based compound semiconductor layer22as in Example 1, it is assumed that the hole concentration in the active layer increases, and high light emission efficiency can be achieved in the range from the low operating current density to the high operating current density.

Example 2 relates to a modification of the GaN-based semiconductor light-emitting element in Example 1, and relates to the methods of manufacturing the GaN-based semiconductor light-emitting elements according to the first embodiment and the second embodiment.

FIG. 3shows a structure including a first GaN-based compound semiconductor layer, an active layer, a laminated structure (a third GaN-based compound semiconductor layer), a second GaN-based compound semiconductor layer, etc. In a GaN-based semiconductor light-emitting element1in Example 2, an undoped GaN-based compound semiconductor layer143constituting a laminate unit141includes a GaN-based compound semiconductor layer, the composition of which contains indium, (specifically, an InGaN layer), or an undoped GaN-based compound semiconductor layer153disposed on a third GaN-based compound semiconductor layer150includes a GaN-based compound semiconductor layer, the composition of which contains indium, (specifically, an InGaN layer).

Alternatively, the undoped GaN-based compound semiconductor layer143constituting the laminate unit141has a three-layer structure including a first layer143A having the same composition as the GaN-based compound semiconductor layer42of p-conductivity type constituting the laminate unit141, a second layer143B having the composition which is the same as the first layer143A and which further contains indium, and a third layer143C having the same composition as the first layer143A. Specifically, the undoped GaN-based compound semiconductor layer143constituting the laminate unit141has a three-layer structure including the first layer143A composed of undoped GaN, the second layer143B composed of undoped InxGa(1-x)N (wherein 0<x≦0.3), and the third layer143C composed of undoped GaN. Furthermore, the active layer23includes an InyGa(1-y)N layer, and x≦y.

Meanwhile, the undoped GaN-based compound semiconductor layer153disposed on the third GaN-based compound semiconductor layer150has a three-layer structure including a first layer153A having the same composition as the third GaN-based compound semiconductor layer150of p-conductivity type, a second layer153B having the composition which is the same as the first layer153A and which further contains indium, and a third layer153C having the same composition as the first layer153A. Specifically, the undoped GaN-based compound semiconductor layer153disposed on the third GaN-based compound semiconductor layer150has a three-layer structure including the first layer153A composed of undoped GaN, the second layer153B composed of undoped InxGa(1-x)N (wherein 0<x≦0.3), and the third layer153C composed of undoped GaN. Furthermore, the active layer23includes an InyGa(1-y)N layer, and x≦y.

More specifically, in Example 2, x=0.23, and y=0.20. Additionally, the difference in the In content can be achieved by forming the GaN-based compound semiconductor layer (second layer143B), the composition of which contains indium, in the undoped GaN-based compound semiconductor layer143constituting the laminate unit141at a higher temperature than the temperature at which the GaN-based compound semiconductor layer, the composition of which contains indium, (specifically, the well layer) in the active layer23is formed. Alternatively, the difference in the In content can be achieved by forming the GaN-based compound semiconductor layer (second layer153B), the composition of which contains indium, in the undoped GaN-based compound semiconductor layer153disposed on the third GaN-based compound semiconductor layer150at a higher temperature than the temperature at which the GaN-based compound semiconductor layer, the composition of which contains indium, (specifically, the well layer) in the active layer23is formed. When the relationship x≦y is satisfied, the bandgap of the second layer143B or153B increases, and as a result, the light generated in the active layer23is less easily absorbed by the second layer143B or153B.

A method of manufacturing a GaN-based semiconductor light-emitting element in Example 2 will be described below. The resulting GaN-based semiconductor light-emitting element1as a whole has substantially the same structure as that shown inFIG. 1A.

First, an underlying layer11and a first GaN-based compound semiconductor layer21are formed on a light-emitting element-forming substrate10as in [Step-100] of Example 1. Furthermore, an active layer23and an impurity diffusion-preventing layer24are formed as in [Step-110] to [Step-120] of Example 1.

Next, by starting supply of Cp2Mg gas as a Mg source, a GaN-based compound semiconductor layer42of p-conductivity type (specifically, Mg-doped GaN layer42) or a third GaN-based compound semiconductor layer150is grown with a thickness of 5 nm. Next, in the state in which the supply of Cp2Mg gas is halted, an undoped GaN-based compound semiconductor layer (a first layer143A having the same composition as the GaN-based compound semiconductor layer42of p-conductivity type constituting the laminate unit141or a first layer153A having the same composition as the third GaN-based compound semiconductor layer150of p-conductivity type) is grown with a thickness of 5 nm. Then, by starting supply of trimethylindium (TMI) gas as an In source, an InGaN layer (a second layer143B having the composition which is the same as the first layer143A and which further contains indium, or a second layer153B having the composition which is the same as the first layer153A and which further contains indium) is grown with a thickness of 3 nm. Next, in the state in which the supply of TMI gas is halted, a GaN layer143C (a third layer143C having the same composition as the first layer143A or a third layer153C having the same composition as the first layer153A) is grown with a thickness of 5 nm. Note that the substrate temperature during the growth of the first layer143A or153A, the second layer143B or153B, and the third layer is set at 760° C. This temperature is higher than 750° C. which is the substrate temperature during the growth of the active layer23. As a result, the compositional proportion of In in the second layer143B or153B composed of InGaN is 0.2. The doping concentration of Mg is about 5×1019/cm3.

In such a manner, at a higher temperature (specifically, 760° C. in Example 2) than the temperature (specifically 750° C. in Example 2) at which the GaN-based compound semiconductor layer, the composition of which contains indium, in the active layer23is formed, the GaN-based compound semiconductor layer, the composition of which contains indium, (second layer143B) in the undoped GaN-based compound semiconductor layer143constituting the laminate unit141is formed, or the GaN-based compound semiconductor layer, the composition of which contains indium, (second layer153B) in the undoped GaN-based compound semiconductor layer153disposed on the third GaN-based compound semiconductor layer150is formed.

The Mg-doped GaN layer42with a thickness of 5 nm and the undoped GaN-based compound semiconductor layer143with a thickness of 13 nm are grown twice repeatedly. Thereby, a laminated structure140including at least one laminate unit141in which the GaN-based compound semiconductor layer42of p-conductivity type and the undoped GaN-based compound semiconductor layer143are stacked in that order from the active layer side can be obtained. Alternatively, a third GaN-based compound semiconductor layer150having at least one undoped GaN-based compound semiconductor layer153(undoped GaN layer153) on the side closer to the second GaN-based compound semiconductor layer22can be obtained.

Subsequently, by carrying out the same steps as [Step-140] to [Step-160] of Example 1, a GaN-based semiconductor light-emitting element1in Example 2 (e.g., any of various types of light-emitting diodes, such as shell-shaped light-emitting diodes and surface-mount-type light-emitting diodes) can be fabricated.

FIG. 4Bis a graph showing the relationship between the operating current density (ampere/cm2) and the light emission efficiency (watt/ampere) in each of Example 2 and Comparative Example 1. As is evident from the graph, Example 2 has a light emission efficiency at the same operating current density that is further increased compared with Example 1 and Comparative Example 1. The increase in the light emission efficiency can be confirmed over the entire range of operating current densities from a common LED operating current density (30 amperes/cm2) to a high operating current density (300 amperes/cm2).

In Example 2, the undoped GaN-based compound semiconductor layer143constituting the laminate unit141includes the GaN-based compound semiconductor layer, the composition of which contains indium, (second layer143B) is disposed, or the undoped GaN-based compound semiconductor layer153disposed on the third GaN-based compound semiconductor layer150includes the GaN-based compound semiconductor layer, the composition of which contains indium, (second layer153B). Such a second layer143B or153B has a narrower bandgap than the first layer143A or153A and the third layer143C or153C because of its composition containing indium, and thus a high hole concentration can be maintained. As a result, the hole concentration in the active layer can be further increased. Consequently, in the GaN-based semiconductor light-emitting element1of Example 2, a higher light emission efficiency can be achieved at the same operating current density compared with Example 1.

In Example 2, the light emission efficiency was measured with respect to GaN-based semiconductor light-emitting elements including the second layer143B or153B with a thickness of 1.5 nm, 3 nm, and 6 nm, respectively. The light emission efficiency was also measured with respect to a GaN-based semiconductor light-emitting element in which the thickness of the second layer143B or153B was set at 0 nm (this GaN-based semiconductor light-emitting element having substantially the same structure as that of the GaN-based semiconductor light-emitting element described in Example 1). The measurement results are shown in the graph ofFIG. 5. In comparison with the case where the thickness of the second layer143B or153B is 0 nm (the curve depicted by hollow diamonds in the graph), each of the case where the thickness of the second layer143B or153B is set at 1.5 nm (the curve depicted by hollow triangles), the case where the thickness of the second layer143B or153B is set at 3 nm (the curve depicted by cross marks), and the case where the thickness of the second layer143B or153B is set at 6 nm (the curve depicted by plus marks) has increased light emission efficiency. On the basis of the results shown inFIG. 5, it is believed that the optimum thickness of the second layer143B or153B is 1 nm to 5 nm.

Example 3 relates to light-emitting element assemblies according to the first embodiment and the second embodiment and image display apparatuses according to the first embodiment and the second embodiment.

FIG. 6is a schematic partial cross-sectional view of a light-emitting element assembly in Example 3. As shown inFIG. 6, the light-emitting element assembly includes a supporting member and a GaN-based semiconductor light-emitting element of Example 1 or Example 2 described above disposed on the supporting member. InFIG. 6, in terms of positional relationship, the GaN-based semiconductor light-emitting element and the supporting member are vertically reversed. Furthermore, an image display apparatus of Example 3 includes a GaN-based semiconductor light-emitting element of Example 1 or Example 2, or a light-emitting element assembly of Example 3 in order to display an image.

A method of manufacturing a light-emitting element assembly of Example 3 will be described with reference toFIGS. 7A,7B,8A,8B,9A,9B,10A,10B,11A, and11B.

First, the same steps as [Step-100] to [Step-150] of Example 1 are carried out, and the same step as [Step-160] of Example 1 is carried out up to the formation of a second electrode32by photolithography, etching, and metal vapor deposition, Alternatively, the same steps as [Step-200] to [Step-220] of Example 2 are carried out (up to the formation of a second electrode32by photolithography, etching, and metal vapor deposition in [Step-220]). Thereby, a GaN-based semiconductor light-emitting element having a trapezoidal cross-section shown inFIG. 7Acan be obtained.

Next, GaN-based semiconductor light-emitting elements1are temporarily fixed onto a temporary fixing substrate60with second electrodes32therebetween. Specifically, the temporary fixing substrate60composed of a glass substrate having an adhesion layer61on the surface thereof is prepared, the adhesion layer61being composed of an uncured adhesive. The GaN-based semiconductor light-emitting elements1and the adhesion layer61are bonded together, and the adhesion layer61is cured. Thus, the GaN-based semiconductor light-emitting elements1can be temporarily fixed onto the temporary fixing substrate60(refer toFIGS. 7B and 8A).

Then, the GaN-based semiconductor light-emitting elements1are detached from the light-emitting element-forming substrate10(refer toFIG. 8B). Specifically, the thickness of the light-emitting element-forming substrate10is decreased by lapping from the back surface. Next, the light-emitting element-forming substrate10and the underlying layer11are subjected to wet etching. Thereby, the light-emitting element-forming substrate10and the underlying layer11are removed to expose the first GaN-based compound semiconductor layer21of each GaN-based semiconductor light-emitting element1.

Examples of the material constituting the temporary fixing substrate60include, besides the glass substrate, a metal plate, an alloy plate, a ceramic plate, and a plastic plate. Examples of the method for temporarily fixing the GaN-based semiconductor light-emitting elements to the temporary fixing substrate60include, besides the method in which an adhesive is used, a metal bonding method, a semiconductor bonding method, and a metal-semiconductor bonding method. Examples of the method for removing the light-emitting element-forming substrate10, etc. from the GaN-based semiconductor light-emitting elements include, besides etching, laser ablation and a heating method.

Next, a first electrode31is formed on the bottom surface of the exposed first GaN-based compound semiconductor layer21. Specifically, using lithography, a resist layer is formed on the entire surface and an opening is formed in the resist layer at a portion on the bottom surface of the first GaN-based compound semiconductor layer21on which the first electrode31is to be formed. Next, the first electrode31composed of a multilayered film including, for example, Au/Pt/Ti/Au/AuGe/Pd stacked in that order is formed on the entire surface by a PVD method, such as vacuum deposition or sputtering, and then the resist layer and the multilayered film on the resist layer are removed.

A transfer substrate70having a slightly adhesive layer71composed of silicone rubber thereon and a mounting substrate80composed of a glass substrate having an alignment mark (not shown) composed of a metal thin film or the like formed at a predetermined position in advance and having an adhesive layer81composed of an uncured photosensitive resin on a surface thereof are prepared.

The adhesive layer81may basically be composed of any material as long as the material exhibits adhesion properties by a certain method, for example, a material which exhibits adhesion properties by irradiation of energy ray, such as light (particularly, ultraviolet light or the like), radiation (e.g., X-ray), or an electron beam; or a material which exhibits adhesion properties by application of heat, pressure, or the like. Examples of the material which can easily form an adhesive layer and which exhibits adhesion properties include resin-based adhesives, in particular, photosensitive adhesives, thermosetting adhesives, and thermoplastic adhesives. For example, when a photosensitive adhesive is used, by irradiating the adhesive layer with light or ultraviolet light or by heating the adhesive layer, adhesion properties can be exhibited. When a thermosetting adhesive is used, by heating the adhesive layer by means of irradiation of light, adhesion properties can be exhibited. When a thermoplastic adhesive is used, part of the adhesive layer is selectively melted by selectively heating by means of irradiation of light or the like, and thus flowability can be imparted thereto. As another example, a pressure-sensitive adhesive layer (composed of an acrylic resin or the like) may be used.

Next, the slightly adhesive layer71is pressed to the GaN-based semiconductor light-emitting elements1remaining in an array (in a two-dimensional matrix) on the temporary fixing substrate60(refer toFIGS. 9A and 9B). Examples of the material that constitutes the transfer substrate70include a glass plate, a metal plate, an alloy plate, a ceramic plate, a semiconductor substrate, and a plastic plate. The transfer substrate70is held by a positioning apparatus (not shown). The positional relationship between the transfer substrate70and the temporary fixing substrate60can be controlled by the operation of the positioning apparatus. Next, for example, excimer laser is applied from the back surface side of the temporary fixing substrate60to the GaN-based semiconductor light-emitting element1to be mounted (refer toFIG. 10A). Thus, laser ablation is caused so that the GaN-based semiconductor light-emitting element1irradiated with excimer laser is detached from the temporary fixing substrate60. Then, the transfer substrate70is separated from the GaN-based semiconductor light-emitting elements1so that the GaN-based semiconductor light-emitting element1detached from the temporary fixing substrate60adheres to the slightly adhesive layer71(refer toFIG. 10B).

Next, the GaN-based semiconductor light-emitting element1is placed on (moved or transferred onto) the adhesive layer81(refer toFIGS. 11A and 11B). Specifically, the GaN-based semiconductor light-emitting element1is transferred from the transfer substrate70onto the adhesive layer81on the mounting substrate80on the basis of the alignment mark disposed on the mounting substrate80. The GaN-based semiconductor light-emitting element1only weakly adheres to the slightly adhesive layer71. Therefore, when the transfer substrate70is moved in a direction away from the mounting substrate80with the GaN-based semiconductor light-emitting element1being in contact with (pressed to) the adhesive layer81, the GaN-based semiconductor light-emitting element1remains on the adhesive layer81. Furthermore, by embedding the GaN-based semiconductor light-emitting element1deeply in the adhesive layer81using a roller or the like, the GaN-based semiconductor light-emitting element (light-emitting diode) can be mounted on the mounting substrate80.

The method using the transfer substrate70as described above is referred to as a “step-transfer method” for convenience sake. By repeating the step-transfer method a desired number of times, a desired number of GaN-based semiconductor light-emitting elements1adhere to the slightly adhesive layer71in a two-dimensional matrix and are transferred onto the mounting substrate80. Specifically, in Example 3, in one step-transfer process, 160×120 GaN-based semiconductor light-emitting elements1, in a two-dimensional matrix, are allowed to adhere to the slightly adhesive layer71and transferred onto the mounting substrate80. Consequently, by repeating the step-transfer method108times {(1,920×1,080)/(160×120)}, 1,920×1,080 GaN-based semiconductor light-emitting elements1can be transferred onto the mounting substrate80. By repeating the above process three times, the predetermined number of red light-emitting diodes, green light-emitting diodes, and blue light-emitting diodes can be mounted on the mounting substrate80at predetermined intervals or pitches.

Then, the adhesive layer81composed of a photosensitive resin, having the GaN-based semiconductor light-emitting elements1thereon, is irradiated with ultraviolet light to cure the photosensitive resin constituting the adhesive layer81. Thereby, the GaN-based semiconductor light-emitting elements1are fixed to the adhesive layer81. Next, each GaN-based semiconductor light-emitting element1is temporarily fixed to a second temporary fixing substrate through the corresponding first electrode31. Specifically, a second temporary fixing substrate composed of a glass substrate having an adhesion layer90composed of an uncured adhesive on a surface thereof is prepared. The GaN-based semiconductor light-emitting element1and the adhesion layer90are bonded together, and the adhesion layer90is cured. Thus, the GaN-based semiconductor light-emitting element1can be temporarily fixed onto the second temporary fixing substrate. Then, the adhesive layer81and the mounting substrate80are removed from the GaN-based semiconductor light-emitting element1by an appropriate method. At this stage, the second electrode32of the GaN-based semiconductor light-emitting element1is exposed.

Next, a second insulating layer91is formed over the entire surface, and an opening92is formed in the second insulating layer91above the second electrode32of the GaN-based semiconductor light-emitting element1. A second line93is formed on the second electrode32so as to extend from the opening92onto the second insulating layer91. Then, by bonding the second insulating layer91including the second line93and a supporting member95composed of a glass substrate to each other through an adhesion layer94. Thereby, the GaN-based semiconductor light-emitting element1can be fixed to the supporting member95. Next, for example, excimer laser is applied from the back surface side of the second temporary fixing substrate. Thus, laser ablation is caused so that the GaN-based semiconductor light-emitting element1irradiated with excimer laser is detached from the second temporary fixing substrate. At this stage, the first electrode31of the GaN-based semiconductor light-emitting element1is exposed. Next, a first insulating layer96is formed over the entire surface, and an opening97is formed in the first insulating layer96above the first electrode31of the GaN-based semiconductor light-emitting element1. A first line98is formed on the first electrode so as to extend from the opening97onto the first insulating layer96.FIG. 6is a schematic partial cross-sectional view showing this state. Then, by connecting the first line and the second line to driving circuits by an appropriate method, a light-emitting element assembly can be obtained, or an image display apparatus (light-emitting diode display apparatus) can be completed. The GaN-based semiconductor light-emitting element1has a flip-chip structure, and light generated by the active layer23is emitted in the lower direction inFIG. 6.

Examples of the image display apparatus of Example 3 include image display apparatuses having the structures described below. Unless otherwise specified, the number of GaN-based semiconductor light-emitting elements constituting an image display apparatus or a light-emitting element panel may be determined on the basis of the specifications of the image display apparatus. Furthermore, the GaN-based semiconductor light-emitting element constituting an image display apparatus or a light-emitting element panel may be any one of the GaN-based semiconductor light-emitting elements described in Examples 1 and 2, or may be the light-emitting element assembly of Example 3. In the latter case, the GaN-based semiconductor light-emitting element1in the following description may be interpreted as a light-emitting element assembly.

(1A) Image Display Apparatus Having a First Structure—A

A passive matrix-type, direct-view-type image display apparatus including (α) a light-emitting element panel200having GaN-based semiconductor light-emitting elements1arranged in a two-dimensional matrix, in which the emission state of each of the GaN-based semiconductor light-emitting elements1is directly visually observed by controlling the emission/non-emission state of each GaN-based semiconductor light-emitting element1to display an image.

FIG. 12Ashows a circuit diagram including a light-emitting element panel200constituting such a passive matrix-type, direct-view-type image display apparatus, andFIG. 12Bis a schematic cross-sectional view showing the light-emitting element panel200in which GaN-based semiconductor light-emitting elements1are arranged in a two-dimensional matrix. One electrode (second electrode or first electrode) of each GaN-based semiconductor light-emitting element1is connected to a column driver221, and the other electrode (first electrode or second electrode) is connected to a row driver222. The emission/non-emission state of each GaN-based semiconductor light-emitting element1is controlled, for example, by the row driver222, and a driving current for driving each GaN-based semiconductor light-emitting element1is supplied from the column driver221. Selection and driving of the individual GaN-based semiconductor light-emitting elements1can be performed by common methods, and the description thereof will be omitted.

The light-emitting element panel200includes a support201, for example, composed of a printed circuit board, (in some cases, corresponding to the supporting member95); GaN-based semiconductor light-emitting elements1mounted on the support201; X-direction lines202which are disposed on the support201, electrically connected to one electrode (second electrode or first electrode) of the respective GaN-based semiconductor light-emitting elements1, and connected to the column driver221or the row driver222; Y-direction lines203which are electrically connected to the other electrode (first electrode or second electrode) of the respective GaN-based semiconductor light-emitting elements1, and connected to the row driver222or the column driver221; a transparent base member204which covers the GaN-based semiconductor light-emitting elements1; and microlenses205provided on the transparent base member204. However, it is to be understood that the light-emitting element panel200is not limited to the structure described above.

(1B) Image Display Apparatus Having the First Structure—B

An active matrix-type, direct-view-type image display apparatus including (α) a light-emitting element panel having GaN-based semiconductor light-emitting elements1arranged in a two-dimensional matrix, in which the emission state of each of the GaN-based semiconductor light-emitting elements1is directly visually observed by controlling the emission/non-emission state of each GaN-based semiconductor light-emitting element1to display an image.

FIG. 13shows a circuit diagram including a light-emitting element panel200constituting such an active matrix-type, direct-view-type image display apparatus. One electrode (second electrode or first electrode) of each GaN-based semiconductor light-emitting element1is connected to a driver225, and the driver225is connected to a column driver223and a row driver224. The other electrode (first electrode or second electrode) of each GaN-based semiconductor light-emitting element1is connected to a ground line. The emission/non-emission state of each GaN-based semiconductor light-emitting element1is controlled by selection of the driver225, for example, by the row driver224, and a luminance signal for driving each GaN-based semiconductor light-emitting element1is supplied from the column driver223to the corresponding driver225. A predetermined voltage is supplied from a power supply (not shown) to each driver225, and the driver225supplies a driving current (PDM-controlled or PWM-controlled) in response to the luminance signal to the corresponding GaN-based semiconductor light-emitting element1. Selection and driving of the individual GaN-based semiconductor light-emitting elements1can be performed by common methods, and the description thereof will be omitted.

(2) Image Display Apparatus Having a Second Structure

A passive matrix-type or active matrix-type, projection-type image display apparatus including (α) a light-emitting element panel200having GaN-based semiconductor light-emitting elements1arranged in a two-dimensional matrix, in which the emission/non-emission state of each GaN-based semiconductor light-emitting element1is controlled to display an image by projection on a screen.

The circuit diagram including a light-emitting element panel constituting such a passive matrix-type image display apparatus is similar to that shown inFIG. 12A, and the circuit diagram including a light-emitting element panel constituting an active matrix-type image display apparatus is similar to that shown inFIG. 13. Thus, the detailed description will be omitted.FIG. 14is a conceptual diagram showing the light-emitting element panel200having GaN-based semiconductor light-emitting elements1arranged in a two-dimensional matrix, etc. Light emitted from the light-emitting element panel200passes through a projector lens206and is projected on a screen. The structure and configuration of the light-emitting element panel200are the same as the structure and configuration of the light-emitting element panel200described with reference toFIG. 12B. Thus, the detailed description thereof will be omitted.

(3) Image Display Apparatus Having a Third Structure

A color image display apparatus (direct-view-type or projection-type) including (α) a red light-emitting element panel200R having red light-emitting semiconductor light-emitting elements R (e.g., AlGaInP-based semiconductor light-emitting elements or GaN-based semiconductor light-emitting elements1R) arranged in a two-dimensional matrix; (β) a green light-emitting element panel200G having green light-emitting GaN-based semiconductor light-emitting elements1G arranged in a two-dimensional matrix; (γ) a blue light-emitting element panel200B having blue light-emitting GaN-based semiconductor light-emitting elements1B arranged in a two-dimensional matrix; and (δ) a device which collects the light emitted from the red light-emitting element panel200R, the green light-emitting element panel200G, and the blue light-emitting element panel200B in an optical path (e.g., a dichroic prism207), in which the emission/non-emission state of each of the red light-emitting semiconductor light-emitting elements R, the green light-emitting GaN-based semiconductor light-emitting elements1G, and the blue light-emitting GaN-based semiconductor light-emitting elements1B is controlled.

The circuit diagram including a light-emitting element panel constituting such a passive matrix-type image display apparatus is similar to that shown inFIG. 12A, and the circuit diagram including a light-emitting element panel constituting an active matrix-type image display apparatus is similar to that shown inFIG. 13. Thus, the detailed description will be omitted.FIG. 15is a conceptual diagram showing the light-emitting element panels200R,200G, and200B having GaN-based semiconductor light-emitting elements R,1G, and1B, respectively, arranged in a two-dimensional matrix, etc. Light emitted from each of the light-emitting element panel200R,200G, and200B enters the dichroic prism207, and the optical paths of the individual light beams are integrated into an optical path. The resulting light is directly visually observed in the case of a direct-view-type image display apparatus, or the resulting light passes through a projector lens206and is projected on a screen in the case of a projection-type image display apparatus. The structure and configuration of each of the light-emitting element panels200R,200G, and200B are the same as the structure and configuration of the light-emitting element panel200described with reference toFIG. 12B. Thus, the detailed description thereof will be omitted.

In such an image display apparatus, desirably, the GaN-based semiconductor light-emitting elements1described in Example: 1 or 2 are used as the semiconductor light-emitting elements R,1G, and1B constituting the light-emitting element panels200R,200G, and200B, respectively. In some cases, AlInGaP-based compound semiconductor light-emitting diodes may be used, for example, as the semiconductor light-emitting elements R constituting the light-emitting element panel200R, and the GaN-based semiconductor light-emitting elements1described in Example 1 or 2 may be used as the GaN-based semiconductor light-emitting elements1G and1B constituting the light-emitting element panels200G and200B, respectively.

(4) Image Display Apparatus Having a Fourth Structure

An image display apparatus (direct-view-type or projection-type) including (α) a GaN-based semiconductor light-emitting element1and (β) a light transmission controller (e.g., a liquid crystal display device208having a high-temperature polysilicon-type thin-film transistor; hereinafter the same) which is a light valve for controlling transmission/non-transmission of light emitted from the GaN-based semiconductor light-emitting element1, in which transmission/non-transmission of light emitted from the GaN-based semiconductor light-emitting element1is controlled by the liquid crystal display device208which is the light transmission controller to display an image.

The number of GaN-based semiconductor light-emitting elements may be determined on the basis of the specifications of the image display apparatus, and may be one or two or more.FIG. 16is a conceptual diagram showing an example of an image display apparatus. In this example, the number of GaN-based semiconductor light-emitting elements1is one, and the GaN-based semiconductor light-emitting element1is fixed to a heat sink210. Light emitted from the GaN-based semiconductor light-emitting element1is guided by a light-guiding member209including an optical guide member composed of a light-transmissive material, such as a silicone resin, an epoxy resin, or a polycarbonate resin, and a reflector, such as a mirror, and is allowed to be incident on the liquid crystal display device208, Light emitted from the liquid crystal display device208is directly visually observed in the case of a direct-view-type image display apparatus, or light emitted from the liquid crystal display device208passes through a projector lens206and is projected on a screen in the case of a projection-type image display apparatus. As the GaN-based semiconductor light-emitting element1, any of the GaN-based semiconductor light-emitting elements described in Examples 1 and 2 can be used.

By designing an image display apparatus which includes a red light-emitting semiconductor light-emitting element R (e.g., an AlGaInP-based semiconductor light-emitting element or a GaN-based semiconductor light-emitting element1R), and a light transmission controller (e.g., a liquid crystal display device208R) which is a light valve for controlling transmission/non-transmission of light emitted from the red light-emitting semiconductor light-emitting element R; a green light-emitting GaN-based semiconductor light-emitting element1G, and a light transmission controller (e.g., a liquid crystal display device208G) which is a light valve for controlling transmission/non-transmission of light emitted from the green light-emitting GaN-based semiconductor light-emitting element1G; a blue light-emitting GaN-based semiconductor light-emitting element1B, and a light transmission controller (e.g., a liquid crystal display device208B) which is a light valve for controlling transmission/non-transmission of light emitted from the blue light-emitting GaN-based semiconductor light-emitting element1B; light-guiding members209R,209G, and209B which guide light emitted from the GaN-based semiconductor light-emitting elements R,1G, and1B, respectively; and a device which collects light in an optical path, a direct-view-type or projection-type color image display apparatus can be obtained.FIG. 17is a conceptual diagram showing an example of a projection-type color image display apparatus.

In such an image display apparatus, desirably, the GaN-based semiconductor light-emitting elements described in Example 1 or Example 2 are used as the semiconductor light-emitting elements R,1G, and1B. In some cases, an AlInGaP-based compound semiconductor light-emitting diode may be used, for example, as the semiconductor light-emitting element R, and the GaN-based semiconductor light-emitting elements described in Example 1 or 2 may be used as the semiconductor light-emitting elements1G and1B.

(5) Image Display Apparatus Having a Fifth Structure

An image display apparatus (direct-view-type or projection-type) including (α) a light-emitting element panel200having GaN-based semiconductor light-emitting elements arranged in a two-dimensional matrix and (β) a light transmission controller (liquid crystal display device208) which controls transmission/non-transmission of light emitted from the GaN-based semiconductor light-emitting elements1, in which transmission/non-transmission of light emitted from the GaN-based semiconductor light-emitting elements1is controlled by the light transmission controller (liquid crystal display device208) to display an image.

FIG. 18is a conceptual diagram showing the light-emitting element panel200, etc. The structure and configuration of the light-emitting element panel200are the same as the structure and configuration of the light-emitting element panel200described with reference toFIG. 12B. Thus, the detailed description thereof will be omitted. Since transmission/non-transmission and brightness of light emitted from the light-emitting element panel200are controlled by the operation of the liquid crystal display device208, GaN-based semiconductor light-emitting elements1constituting the light-emitting element panel200may be constantly turned on or may be turned on and off repeatedly in an appropriate cycle. Light emitted from the light-emitting element panel200enters the liquid crystal display device208. Light emitted from the liquid crystal display device208is directly visually observed in the case of a direct-view-type image display apparatus, or light emitted from the liquid crystal display device208passes through a projector lens206and is projected on a screen in the case of a projection-type image display apparatus.

(6) Image Display Apparatus Having a Sixth Structure

A color image display apparatus (direct-view-type or projection-type) including (α) a red light-emitting element panel200R having red light-emitting semiconductor light-emitting elements R (e.g., AlGaInP-based semiconductor light-emitting elements or GaN-based semiconductor light-emitting elements1R) arranged in a two-dimensional matrix, and a red light transmission controller (liquid crystal display device208R) which controls transmission/non-transmission of light emitted from the red light-emitting element panel200R; (β) a green light-emitting element panel200G having green light-emitting GaN-based semiconductor light-emitting elements1G arranged in a two-dimensional matrix, and a green light transmission controller (liquid crystal display device208G) which controls transmission/non-transmission of light emitted from the green light-emitting element panel200G; (γ) a blue light-emitting element panel200B having blue light-emitting GaN-based semiconductor light-emitting elements1B arranged in a two-dimensional matrix, and a blue light transmission controller (liquid crystal display device208B) which controls transmission/non-transmission of light emitted from the blue light-emitting element panel200B; and (δ) a device (e.g., dichroic prism207) which collects the light transmitted through the red light transmission controller208R, the green light transmission controller208G, and the blue light transmission controller208G in an optical path, in which the transmission/non-transmission of light emitted from the light-emitting element panels200R,200G, and200B is controlled by the corresponding light transmission controllers208R,208G, and208B to display an image.

FIG. 19is a conceptual diagram showing the light-emitting element panels200R,200G, and200B having GaN-based semiconductor light-emitting elements R,1G, and1B, respectively, arranged in a two-dimensional matrix, etc. Light emitted from the light-emitting element panel200R,200G, and200B, the transmission/non-transmission of which are controlled by the light transmission controllers208R,208G,208B, respectively, enters the dichroic prism207. The optical paths of the individual light beams are integrated into an optical path. The resulting light is directly visually observed in the case of a direct-view-type image display apparatus, or the resulting light passes through a projector lens206and is projected on a screen in the case of a projection-type image display apparatus. The structure and configuration of each of the light-emitting element panels200R,200G, and200B are the same as the structure and configuration of the light-emitting element panel200described with reference toFIG. 12B. Thus, the detailed description thereof will be omitted.

In such an image display apparatus, desirably, the GaN-based semiconductor light-emitting elements1described in Example 1 or 2 are used as the semiconductor light-emitting elements R,1G, and1B constituting the light-emitting element panels200R,200G, and200B, respectively. In some cases, AlInGaP-based compound semiconductor light-emitting diodes may be used, for example, as the semiconductor light-emitting elements R constituting the light-emitting element panel200R, and the GaN-based semiconductor light-emitting elements1described in Example 1 or Example 2 may be used as the GaN-based semiconductor light-emitting elements1G and1B constituting the light-emitting element panels200G and200B, respectively.

(7) Image Display Apparatus Having a Seventh Structure

A field-sequential color image display apparatus (direct-view-type or projection-type) including (α) a red light-emitting semiconductor light-emitting element R (e.g., AlGaInP-based semiconductor light-emitting element or GaN-based semiconductor light-emitting element1R); (β) a green light-emitting GaN-based semiconductor light-emitting element1G; (γ) a blue light-emitting GaN-based semiconductor light-emitting element1B; (δ) a device (e.g., dichroic prism207) which collects the light emitted from the red light-emitting semiconductor light-emitting element R, the green light-emitting GaN-based semiconductor light-emitting element1G, and the blue light-emitting GaN-based semiconductor light-emitting element1B in an optical path; and (∈) a light transmission controller (liquid crystal display device208) which controls transmission/non-transmission of light emitted from the device (dichroic prism207) which collects the light in the optical path, in which the transmission/non-transmission of light emitted from each of the light-emitting elements is controlled by the light transmission controller208to display an image.

FIG. 20is a conceptual diagram showing the semiconductor light-emitting elements R,1G, and1B, etc. Light emitted from each of the semiconductor light-emitting elements R,1G, and1B enters the dichroic prism207, and the optical paths of the individual light beams are integrated into an optical path. The resulting light is directly visually observed in the case of a direct-view-type image display apparatus, or the resulting light passes through a projector lens206and is projected on a screen in the case of a projection-type image display apparatus. In such an image display apparatus, desirably, the GaN-based semiconductor light-emitting elements1described in Example 1 or 2 are used as the semiconductor light-emitting elements R,1G, and1B. In some cases, an AlInGaP-based compound semiconductor light-emitting diode may be used, for example, as the semiconductor light-emitting element R, and the GaN-based semiconductor light-emitting elements1described in Example 1 or 2 may be used as the GaN-based semiconductor light-emitting elements1G and1B.

(8) Image Display Apparatus Having an Eighth Structure

A field-sequential color image display apparatus (direct-view-type or projection-type) including (α) a red light-emitting element panel200R having red light-emitting semiconductor light-emitting elements R (e.g., AlGaInP-based semiconductor light-emitting elements or GaN-based semiconductor light-emitting elements1R) arranged in a two-dimensional matrix; (β) a green light-emitting element panel200G having green light-emitting GaN-based semiconductor light-emitting elements1G arranged in a two-dimensional matrix; (γ) a blue light-emitting element panel200B having blue light-emitting GaN-based semiconductor light-emitting elements1B arranged in a two-dimensional matrix; (δ) a device (e.g., dichroic prism207) which collects the light emitted from the red light-emitting element panel200R, the green light-emitting element panel200G, and the blue light-emitting element panel200B in an optical path; and (∈) a light transmission controller (liquid crystal display device208) which controls transmission/non-transmission of light emitted from the device (dichroic prism207) which collects the light in the optical path, in which the transmission/non-transmission of light emitted from each of the light-emitting element panels200R,200G, and200B is controlled by the light transmission controller208to display an image.

FIG. 21is a conceptual diagram showing the light-emitting element panels200R,200G, and200B having GaN-based semiconductor light-emitting elements R,1G, and,1B, respectively, arranged in a two-dimensional matrix, etc. Light emitted from the light-emitting element panel200R,200G, and200B enters the dichroic prism207. The optical paths of the individual light beams are integrated into an optical path. The transmission/non-transmission of the light emitted from the dichroic prism207is controlled by the light transmission controller208. The resulting light is directly visually observed in the case of a direct-view-type image display apparatus, or the resulting light passes through a projector lens206and is projected on a screen in the case of a projection-type image display apparatus. The structure and configuration of each of the light-emitting element panels200R,200G, and200B are the same as the structure and configuration of the light-emitting element panel200described with reference toFIG. 12B. Thus, the detailed description thereof will be omitted.

In such an image display apparatus, desirably, the GaN-based semiconductor light-emitting elements1described in Example 1 or 2 are used as the semiconductor light-emitting elements R,1G, and1B constituting the light-emitting element panels200R,200G, and200B, respectively. In some cases, AlInGaP-based compound semiconductor light-emitting diodes may be used, for example, as the semiconductor light-emitting elements R constituting the light-emitting element panel200R, and the GaN-based semiconductor light-emitting elements1described in Example 1 or 2 may be used as the GaN-based semiconductor light-emitting elements1G and1B constituting the light-emitting element panels200G and200B, respectively.

Example 4 also relates to image display apparatuses according to the first embodiment and the second embodiment. An image display apparatus of Example 4 includes light-emitting element units UN for displaying a color image arranged in a two-dimensional matrix, each light-emitting element unit UN including a blue light-emitting first light-emitting element, a green light-emitting second light-emitting element, and a red light-emitting third light-emitting element. As in Example 3, the GaN-based semiconductor light-emitting element (light-emitting diode) constituting at least one of the first light-emitting element, the second light-emitting element, and the third light-emitting element may have the same basic configuration and structure as those of the GaN-based semiconductor light-emitting element described in Example 1 or 2, or may be the light-emitting element assembly of Example 3. In the latter case, the GaN-based semiconductor light-emitting element1in the following description may be interpreted as a light-emitting element assembly. In such an image display apparatus, as any one of the first light-emitting element, the second light-emitting element, and the third light-emitting element, the GaN-based semiconductor light-emitting element1described in Example 1 or 2 is used. In some cases, the red light-emitting element may be constituted by an AlInGaP-based compound semiconductor light-emitting diode.

Examples of the image display apparatus of Example 4 include image display apparatuses having the structures described below. The number of light-emitting element units UN may be determined on the basis of the specifications of the image display apparatus.

(1) Image Display Apparatuses Having a Ninth Structure and a Tenth Structure

A passive matrix-type or active matrix-type, direct-view-type color image display apparatus including a first light-emitting element, a second light-emitting element, and a third light-emitting element, in which the emission state of each of the light-emitting elements is directly visually observed by controlling the emission/non-emission state of each light-emitting element to display an image, and a passive matrix-type or active matrix-type, projection-type color image display apparatus including a first light-emitting element, a second light-emitting element, and a third light-emitting element, in which the emission/non-emission state of each of the light-emitting elements is controlled to display an image by projection on a screen.

FIG. 22is a circuit diagram including a light-emitting element panel constituting such an active matrix-type, direct-view-type color image display apparatus. One electrode (second electrode or first electrode) of each GaN-based semiconductor light-emitting element1(inFIG. 22, a red light-emitting semiconductor light-emitting element being represented by “R”, a green light-emitting GaN-based semiconductor light-emitting element being represented by “G”, and a blue light-emitting GaN-based semiconductor light-emitting element being represented by “B”) is connected to the corresponding driver225, and each driver225is connected to a column driver223and a row driver224. The other electrode (first electrode or second electrode) is connected to a ground line. The emission/non-emission state of each GaN-based semiconductor light-emitting element1is controlled, for example, by selection of the corresponding driver225by the row driver224, and a luminance signal for driving each GaN-based semiconductor light-emitting element1is supplied from the column driver223to the corresponding driver225. A predetermined voltage is supplied from a power supply (not shown) to each driver225, and the driver225supplies a driving current (PDM-controlled or PWM-controlled) in response to the luminance signal to the corresponding GaN-based semiconductor light-emitting element1. The red light-emitting semiconductor light-emitting element R, the green light-emitting GaN-based semiconductor light-emitting element G, and the blue light-emitting GaN-based semiconductor light-emitting element B are selected by the corresponding driver225, and red light-emitting semiconductor light-emitting element R, the green light-emitting GaN-based semiconductor light-emitting element G, and the blue light-emitting GaN-based semiconductor light-emitting element B may be controlled by time sharing, or simultaneous light emission may be performed. Selection and driving of the individual GaN-based semiconductor light-emitting elements1can be performed by common methods, and the description thereof will be omitted. The resulting light is directly visually observed in the case of a direct-view-type image display apparatus, or the resulting light passes through a projector lens and is projected on a screen in the case of a projection-type image display apparatus.

(2) Image Display Apparatus Having an Eleventh Structure

A field-sequential color image display apparatus (direct-view-type or projection-type) including light-emitting element units arranged in a two-dimensional matrix, and a light transmission controller (e.g., liquid crystal display device) which controls transmission/non-transmission of light emitted from the light-emitting element units, in which the emission/non-emission state of each of a first light-emitting element, a second light-emitting element, and a third light-emitting element in each light-emitting element unit is controlled by time sharing, and the transmission/non-transmission of light emitted from the first light-emitting element, the second light-emitting element, and the third light-emitting element is controlled by the light transmission controller to display an image.

The conceptual diagram of such an image display apparatus is the same as that shown inFIG. 14. The resulting light is directly visually observed in the case of a direct-view-type image display apparatus, or the resulting light passes through a projector lens and is projected on a screen in the case of a projection-type image display apparatus.

Example 5 relates to light-emitting apparatuses according to the first embodiment and the second embodiment. A light-emitting apparatus of Example 5 includes any of the GaN-based semiconductor light-emitting elements1described in Examples 1 and 2, and a color conversion material which is excited by emitted light from the GaN-based semiconductor light-emitting element1to emit light with a different wavelength from that of the emitted light from the GaN-based semiconductor light-emitting element1. The color conversion material is, for example, applied onto a light-emitting portion of a GaN-based semiconductor light-emitting element1. Alternatively, the color conversion material in the form of a film is attached to the GaN-based semiconductor light-emitting element1. In the light-emitting apparatus of Example 5, examples of emitted light from the GaN-based semiconductor light-emitting element1include visible light, ultraviolet light, and a combination of visible light and ultraviolet light. The GaN-based semiconductor light-emitting element1may be replaced with the light-emitting element assembly of Example 3. In such a case, the GaN-based semiconductor light-emitting element1in the following description may be interpreted as a light-emitting element assembly.

In the light-emitting apparatus of Example 5, a structure may be employed in which the light emitted from the GaN-based semiconductor light-emitting element1is blue light, and the light emitted from the color conversion material is at least one type of light selected from the group consisting of yellow light, green light, and red light. Alternatively, a structure may be employed in which the light emitted from the GaN-based semiconductor light-emitting element1and the light emitted from the color conversion material (e.g., yellow; red and green; yellow and red; or green, yellow, and red) are mixed to emit white light. The structure of the light-emitting apparatus is not limited thereto, and the light-emitting apparatus can also be applied to variable color illumination and displays.

More specifically, in Example 5, emitted light from the GaN-based semiconductor light-emitting element1is blue light, emitted light from the color conversion material is yellow light, and the color conversion material is composed of YAG (yttrium-aluminum-garnet)-based fluorescent particles. The emitted light (blue) from the GaN-based semiconductor light-emitting element1and the emitted light (yellow) from the color conversion material are mixed to emit white light.

Alternatively, in Example 5, emitted light from the GaN-based semiconductor light-emitting element1is blue light, and emitted light from the color conversion material is composed of green light and red light. The emitted light (blue) from the GaN-based semiconductor light-emitting element1and the emitted light (green and red) from the color conversion material are mixed to emit white light. In this case, the green-light emitting color conversion material is composed of green light-emitting fluorescent particles, such as SrGa2S4:Eu, which are excited by blue light emitted from the GaN-based semiconductor light-emitting element1. The red light-emitting color conversion material is composed of red light-emitting fluorescent particles, such as CaS:Eu, which are excited by blue light emitted from the GaN-based semiconductor light-emitting element1.

Example 6 is an example in which the GaN-based semiconductor light-emitting elements described in Example 1 or 2 are applied to a planar light-source device and a liquid crystal display device assembly (specifically, a color liquid crystal display device assembly). The planar light-source device of Example 6 applies light to a transmissive or semi-transmissive color liquid crystal display device from the back surface side. The color liquid crystal display device assembly of Example 6 includes a transmissive or semi-transmissive color liquid crystal display device and a planar light-source device which applies light to the color liquid crystal display device from the back surface side. GaN-based semiconductor light-emitting elements (light-emitting diodes)1R,1G, and1B provided as light sources in the planar light-source device have the same basic configuration and structure as those of the GaN-based semiconductor light-emitting element described in Example 1 or 2. The GaN-based semiconductor light-emitting elements1R,1G, and1B may be replaced with the light-emitting element assemblies of Example 3. In such a case, the GaN-based semiconductor light-emitting elements1R,1G, and1B in the following description may be interpreted as light-emitting element assemblies.

FIG. 23Aschematically shows the arrangement of GaN-based semiconductor light-emitting elements (light-emitting diodes)1R,1G, and1B in a planar light-source device of Example 6.FIG. 23Bis a schematic partial cross-sectional view of a planar light-source device and a color liquid crystal display device assembly.FIG. 24is a schematic partial cross-sectional view of a color liquid crystal display device.

Specifically, a color liquid crystal display device assembly300of Example 6 includes a transmissive color liquid crystal display device310including (a) a front panel320having a transparent first electrode324, (b) a rear panel330having a transparent second electrode334, and (c) a liquid crystal material327placed between the front panel320and the rear panel330; and (d) a planar light-source device (direct-type backlight)340having semiconductor light-emitting elements1R,1G, and1B as light sources. The planar light-source device (direct-type backlight)340is disposed so as to face the rear panel330, and applies light from the rear panel side to the color liquid crystal display device310.

The direct-type planar light-source device340includes a housing341having an outer frame343and an inner frame344. The end of the transmissive color liquid crystal display device310is held so as to be sandwiched between the outer frame343and the inner frame344through spacers345A and345B, respectively. A guiding member346is disposed between the outer frame343and the inner frame344so that the color liquid crystal display device310sandwiched between the outer frame343and the inner frame344is prevented from deviating from the proper position. A diffuser plate351is fixed to the inner frame344through a spacer345C and a bracket member347at the upper portion in the housing341. An optical functional sheet group including a diffuser sheet352, a prism sheet353, and a polarization conversion sheet354is disposed on the diffuser plate351.

A reflection sheet355is provided at the lower portion in the housing341. The reflection sheet355is arranged so that the reflection surface thereof faces the diffuser plate351, and is fixed to a bottom surface342A of the housing341through a fixing member (not shown). The reflection sheet355can be composed of a high-reflection silver film, for example, having a structure in which a silver reflection film, a low-refractive-index film, and a high-refractive-index film are disposed in that order on a sheet substrate. The reflection sheet355reflects light emitted from a plurality of red light-emitting GaN-based semiconductor light-emitting elements1R (or GAlGaInP-based semiconductor light-emitting elements), a plurality of green light-emitting GaN-based semiconductor light-emitting elements1G, and a plurality of blue light-emitting GaN-based semiconductor light-emitting elements1B, and light reflected by a side surface342B of the housing341. Thus, red light, green light, and blue light emitted from a plurality of semiconductor light-emitting elements1R,1G, and1B are mixed, and white light with high color purity can be obtained as illuminating light. The illuminating light passes through the diffuser plate351, and the optical functional sheet group including the diffuser sheet352, the prism sheet353, and the polarization conversion sheet354, and is applied to the color liquid crystal display device310from the back surface side.

With respect to the arrangement of the light-emitting elements, for example, a plurality of light-emitting element rows are arranged in the horizontal direction to form a light-emitting element row array, each light-emitting element row including a predetermined number of red light-emitting GaN-based semiconductor light-emitting elements1R (or AlGaInP-based semiconductor light-emitting elements), green light-emitting GaN-based semiconductor light-emitting elements1G, and blue light-emitting GaN-based semiconductor light-emitting elements1B, and a plurality of such light-emitting element row arrays are arranged in the vertical direction. The light-emitting element row is, for example, composed of two red light-emitting AlGaInP-based semiconductor light-emitting elements, two green light-emitting GaN-based semiconductor light-emitting elements, and one blue light-emitting GaN-based semiconductor light-emitting element, and a red light-emitting AlGaInP-based semiconductor light-emitting element, a green light-emitting GaN-based semiconductor light-emitting element, a blue light-emitting GaN-based semiconductor light-emitting element, a green light-emitting GaN-based semiconductor light-emitting element, and a red light-emitting AlGaInP-based semiconductor light-emitting element are arranged in that order.

As shown inFIG. 24, the front panel320constituting the color liquid crystal display device310includes a first substrate321, for example, composed of a glass substrate, and a polarization film326disposed on the outer surface of the first substrate321. A color filter322coated with an overcoat layer323composed of an acrylic resin or an epoxy resin is disposed on the inner surface of the first substrate321, and a transparent first electrode (also referred to as a common electrode, for example, composed of ITO)324is disposed on the overcoat layer323. An alignment layer325is disposed on the transparent first electrode324. Meanwhile, the rear panel330includes a second substrate331, for example composed of a glass substrate, switching elements (specifically, thin-film transistors, TFTs)332disposed on the inner surface of the second substrate331, transparent second electrodes (also referred to as pixel electrodes, for example, composed of ITO)334, the conduction/non-conduction of the second electrodes being controlled by the switching elements332, and a polarization film336disposed on the outer surface of the second substrate331. An alignment layer335is disposed over the entire surface including the transparent second electrodes334. The front panel320and the rear panel330are bonded to each other at the outer peripheries thereof by a sealing member (not shown). The switching elements332are not limited to TFTs, and, for example, may be composed of MIM elements. InFIG. 24, reference numeral337represents an insulating layer disposed between the switching elements332.

The various members constituting the transmissive color liquid crystal display device and the liquid crystal material can be composed of commonly used members and materials, and thus the detailed description thereof will be omitted.

Furthermore, by dividing the planar light-source device into a plurality of regions and by dynamically controlling each region independently, the dynamic range with respect to the luminance of the color liquid crystal display device can be further enlarged. That is, the planar light-source device is divided into a plurality of regions for each image display frame, and the brightness of the planar light-source device is changed according to an image signal in each region (for example, the luminance of each region of the planar light-source device is changed in proportion to the maximum luminance of the corresponding region of an image). In this case, in a bright region of an image, the corresponding region of the planar light-source device is brightened, while in a dark region of an image, the corresponding region of the planar light-source device is darkened, so that the contrast ratio of the color liquid crystal display device can be significantly improved. Furthermore, the average electrical power consumption can be decreased. In this technique, it is important to decrease color variations between the regions of the planar light source device. In GaN-based semiconductor light-emitting elements, variations easily occur in luminous colors during the manufacture. However, the GaN-based semiconductor light-emitting elements used in Example 6 are the same GaN-based semiconductor light-emitting elements as those described in Examples 1 and 2, and thus a planar light-source device with small variations in luminous colors between the regions can be achieved. Moreover, in addition to the control of the operating current density (or driving current) of the GaN-based semiconductor light-emitting element as the light source, the luminance (brightness) of the GaN-based semiconductor light-emitting element as the light source can be controlled by controlling the pulse width of the driving current and/or the pulse density of the driving current. Therefore, each of a plurality of divided regions can be independently, dynamically controlled more reliably and easily. Specifically, for example, the luminance of each region of the planar light-source device may be controlled by the peak current value of the driving current (operating current), and the luminance may be finely controlled by controlling the pulse width and/or pulse density of the driving current. Alternatively, conversely to this, the luminance of the entire planar light-source device may be controlled by controlling the pulse width and/or pulse density of the driving current, and the luminance may be finely controlled by the peak current value of the driving current (operating current).

Example 7 is a modification of Example 6 Example 6 relates to a direct-type planar light-source device, while Example 7 relates to an edge light-type planar light-source device.FIG. 25is a conceptual diagram showing a color liquid crystal display device assembly of Example 7. The schematic partial cross-sectional view of the color liquid crystal display device in Example 7 is the same as the schematic partial cross-sectional view shown inFIG. 24.

A color liquid crystal display device assembly300A of Example 7 includes a transmissive color liquid crystal display device310including (a) a front panel320having a transparent first electrode324, (b) a rear panel330having a transparent second electrode334, and (c) a liquid crystal material327placed between the front panel320and the rear panel330; and (d) a planar light-source device (edge light-type backlight)350which is composed of a light guide plate370and a light source360and which applies light from the rear panel side to the color liquid crystal display device310. The light guide plate370is disposed so as to face the rear panel330.

The light source360is, for example, composed of a red light-emitting AlGaInP-based semiconductor light-emitting element, a green light-emitting GaN-based semiconductor light-emitting element, and a blue light-emitting GaN-based semiconductor light-emitting element. These semiconductor light-emitting elements are not shown inFIG. 25. As the green light-emitting GaN-based semiconductor light-emitting element and the blue light-emitting GaN-based semiconductor light-emitting element, the same GaN-based semiconductor light-emitting elements as those described in Example 1 or 2 can be used. Furthermore, the front panel320and the rear panel330constituting the color liquid crystal display device310can have the same configurations and structures as the configurations and structures of the front panel320and the rear panel336of Example 6 described with reference toFIG. 24, and thus the detailed description thereof will be omitted.

The light guide plate370, for example, composed of a polycarbonate resin, has a first surface (bottom surface)371, a second surface (top surface)373opposite the first surface371, a first side surface374, a second side surface375, a third side surface376opposite the first side surface374, and a fourth side surface opposite the second side surface375. More specifically, the light guide plate370as a whole has a wedge-like, truncated quadrangular pyramid shape. Two opposing side surfaces of the truncated quadrangular pyramid correspond to the first surface371and the second surface373, and the bottom surface of the truncated quadrangular pyramid corresponds to the first side surface374. The first surface371has an irregular portion372. When the light guide plate370is cut along a phantom plane extending in the light-incident direction to the light guide plate370and perpendicular to the first surface371, the cross-sectional shape of the continuously irregular portion is triangular. That is, the irregular portion372provided on the first surface371is prismatic. The second surface373of the light guide plate370may be a smooth surface (i.e., mirror surface), or may be provided with blast irregularities having a diffusion effect (i.e., a fine irregular surface). A reflection member381is arranged so as to face the first surface371of the light guide plate370. The color liquid crystal display device310is arranged so as to face the second surface373of the light guide plate370. Furthermore, a diffuser sheet382and a prism sheet383are arranged between the color liquid crystal display device310and the second surface373of the light guide plate370. Light emitted from the light source360enters the light guide plate370from the first side surface374(e.g., surface corresponding to the bottom surface of the bottom surface of the truncated quadrangular pyramid), is scattered by collision with the irregular portion372on the first surface371, is emitted from the first surface371, is reflected by the reflection member381, again enters the first surface371, is emitted from the second surface373, passes through the diffuser sheet382and the prism sheet383, and then is applied to the color liquid crystal display device310.

The present application has been described on the basis of the preferred Examples. However, the present application is not limited to these Examples. The configurations and structures of the GaN-based semiconductor light-emitting elements described in Examples, and the light-emitting element assemblies, light-emitting apparatuses, image display apparatuses, planar light-source devices, or the color liquid crystal display device assemblies having the GaN-based semiconductor light-emitting elements therein are merely exemplification, and the members, materials, and the like constituting these are merely exemplification. These can be altered appropriately. The order of deposition in a GaN-based semiconductor light-emitting element may be reversed. The direct-view-type image display apparatus may be designed to be an image display apparatus in which an image is projected on the human retina. The GaN-based semiconductor light-emitting element may constitute a semiconductor laser.