SEMICONDUCTOR LIGHT EMITTING DEVICE

A semiconductor light emitting device includes: a semiconductor laminate having first and second conductivity type semiconductor layers and an active layer formed between the first and second conductivity type semiconductor layers; first and second electrodes connected to the first and second conductivity type semiconductor layers, respectively; and a micro-pattern formed on a light emitting surface from which light generated from the active layer is output, wherein a section of the micro-pattern parallel to the light emitting surface has a polygonal shape.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1is a schematic perspective view of a semiconductor light emitting device according to an embodiment of the present invention.

As illustrated inFIG. 1, a semiconductor light emitting device10according to the present embodiment includes a semiconductor laminate15formed on a substrate11. The semiconductor laminate15includes first and second conductivity type semiconductor layers15aand15cand an active layer15bformed therebetween.

The first conductivity type semiconductor layer15amay be a group III-V nitride semiconductor layer, for example, an n-GaN layer. The second conductivity type semiconductor layer15cmay be a group III-V nitride semiconductor layer, for example, a p-GaN layer or a p-GaN/AlGaN layer.

The active layer15bmay be a group III-V nitride semiconductor layer of a GaN group of InxAlyGa1-x-yN (0≦x<1, 0≦y<1, and 0≦x+y<1), and may be a multi-quantum well (MQW) or a single quantum well. For example, the active layer15bmay have a GaN/InGaN/GaN MQW or GaN/AlGaN/GaN MQW structure.

First and second electrodes19aand19bare formed to be connected to the first and second conductivity type semiconductor layers15aand15c, respectively. The first electrode19aand the second electrode19bmay include a contact electrode material that may be a metal such as nickel (Ni), aluminum (Al), silver (Ag), gold (Au) or a transparent conductive material, and may have a multilayered structure including two or more layers. In order to be connected to an external circuit, the first electrode19aand the second electrode19bmay further include an electrode bonding material such as gold (Au). In this case, a barrier metal layer such as titanium (Ti) may be further provided between the contact electrode and the bonding electrode, as necessary.

In the present embodiment, a transparent electrode layer17may be formed on the second conductivity type semiconductor layer15c. The transparent electrode layer17may be formed of a transparent conductive oxide. For example, a material used to form the transparent electrode may be any one selected from the group consisting of indium tin oxide (ITO), zinc-doped indium tin oxide (ZITO), zinc indium oxide (ZIO), gallium indium oxide (GIO), zinc tin oxide (ZTO), fluorine-doped tin oxide (FTC)), aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), In4Sn2O12and Zn(1-x)MgxO (zinc magnesium oxide, 0≦x≦1). Specifically, the material may include Zn2In2O5, GaInO3, ZnSnO3, F-doped SnO2, Al-doped ZnO, Ga-doped ZnO, MgO, ZnO, and the like.

In the semiconductor light emitting device, when a predetermined voltage is applied between the first electrode19aand the second electrode19b, electrons and holes are injected from the first conductivity type semiconductor layer15aand the second conductivity type semiconductor layer15cto the active layer15band recombined in the active layer15bto generate light therefrom.

A light emitting surface of the semiconductor light emitting device10includes a micro-pattern18. Here, the light emitting surface refers to a particular surface of the light emitting device10from which light generated in the active layer15bis output.

In the present embodiment, the light emitting surface is illustrated as a surface on the second conductivity type semiconductor layer15c, strictly speaking, a surface of the transparent electrode layer17, but it may be a surface in relation to a different semiconductor layer or one surface of the substrate according to a structure of the semiconductor light emitting device.

In the present embodiment, as illustrated inFIG. 2, the micro-pattern18has a triangular pyramidal shape, and a triangular section of the triangular pyramid is parallel to the light emitting surface.

As illustrated inFIG. 3, when viewed from above, the micro-pattern has three angled portions. The provision of the angled portions formed on lateral portions of the micro-pattern18may greatly contribute to the effective extraction of light. Namely, such angled portions may advantageously act to enhance light extraction efficiency relative to a pattern having a gentle lateral surface, e.g., a hemispherical pattern. Thus, by applying the angled portions to the lateral surfaces of the micro-pattern, a light extraction effect can be increased

Preferably, the angled portions employed in the micro-pattern may have a right angle or an acute angle (i.e., an angle at which an internal angle toward the center of the section is equal to or less than 90°) in terms of light extraction efficiency.

The micro-pattern18illustrated inFIGS. 2 and 3is illustrated as having a triangular pyramidal shape having an equilateral triangular section (or bottom surface) in which internal angles are 60°, respectively, but the present invention is not limited thereto. For example, the micro-pattern18may have a pillar structure having the same shape.

FIG. 4illustrates a micro-pattern28having a pillar structure, rather than having a projection structure (i.e., a pointed tip structure), although it has an equilateral triangular section similar to the sectional shape illustrated inFIG. 3. The micro-pattern28illustrated inFIG. 4may also have angled portions on lateral portions to reinforce the light extraction function.

In another example, a section of a micro-pattern may have various polygonal shapes.FIGS. 5A to 5CandFIGS. 6A to 6Cillustrate some examples thereof.

First, referring toFIGS. 5A to 5C, it is illustrated that a quadrangular pillar (FIG. 5A) has a substantially square cross-section, a quadrangular pillar (FIG. 5B) has a parallelogram as a cross-sectional shape, and a pillar (FIG. 5C) has a cross-section similar to that of a dagger.

The section of the micro-pattern illustrated inFIG. 5Chas four sharply angled portions. Namely, the micro-pattern may have a shape having a plurality of tip portions in which the internal angles θ1 toward the center of the section are less than 60°. In the present embodiment, the provision of a plurality of tip portions having sharp internal angles less than 60° may drastically increase light extraction efficiency due to the angled portions on the lateral portions of the fine pattern. As the sectional shape, various shapes similar to a star-like shape, and the like, may be considered.

Referring toFIGS. 6A to 6C, micro-patterns each of which having a structure having a pyramidal shape different from the shapes of the foregoing examples, while having the sections corresponding to the sectional shapes illustrated inFIGS. 5A to 5C, are illustrated. As illustrated inFIGS. 6A to 6C, the micro-patterns may be implemented to have various pyramid structures such as a quadrangular pyramid (FIG. 6A) having a substantially square cross-section, a quadrangular pyramid (FIG. 6B) having a parallelogram as a cross-sectional shape, and a pyramid (FIG. 6C) having a cross-section similar to that of a dragger.

The improvement effect of light extraction efficiency by employing the angled portions on the lateral portions of the micro-pattern as described above was confirmed through an experiment conduced under the following conditions by using various patterns.

Three nitride semiconductor light emitting devices were fabricated as follows. Namely, an n-type GaN layer, an active layer having an InGaN/GaN multi-quantum well (MQW) structure, and a p-type AlGaN/GaN layer were grown on a sapphire substrate, and an ITO layer having a thickness of approximately 150 nm was formed on a surface of the p-type GaN layer, as a transparent electrode layer.

Subsequently, portions of the n-type GaN layer were exposed by applying mesa etching, and an n-side electrode and a A-side electrode were subsequently formed on exposed n-type GaN layer regions and ITO layer regions, respectively.

A layer for a micro-pattern was formed on the ITO layer to have a uniform thickness of 0.7 μm, and a square pillar micro-pattern having a square section was fabricated (Please seeFIG. 5(a)).

Also, micro-patterns implemented in three nitride semiconductor light emitting devices were formed to have different sizes. Namely, micro-patterns were formed such that lengths (a) of one side of the square section were differentiated to be 4 μm, 6 μm, and 8 μm, respectively. Here, a charge rate of the patterns (i.e., an occupancy area rate of the patterns) was designed to be 19.6%.

Nitride semiconductor light emitting devices were fabricated under the same conditions as those of Embodiment 1, and micro-patterns were fabricated to have a trigonal prism cross-section (Please seeFIG. 4). Also, the micro-patterns were formed such that lengths (a) of one side of the equilateral triangle were differentiated to be 4 μm, 6 μm, and 8 μm and a charge rate (19.6%) of the patterns was uniformly maintained.

Nitride semiconductor light emitting devices were fabricated under the same conditions as those of Embodiment 1, and micro-patterns were fabricated to have a pillar shape having four tip portions in cross-section (Please seeFIG. 5). Also, the micro-patterns were formed such that lengths (a) of one sides of the tip portions were differentiated to be 4 μm, 6 μm, and 8 μm and a charge rate (19.6%) of the patterns was uniformly maintained.

Comparative Example

Nitride semiconductor light emitting devices were fabricated under the same conditions as those of Embodiment 1, and micro-patterns were fabricated to have a cylindrical shape without any angled portions on a lateral portion thereof. Also, the micro-patterns were formed such that diameters of the circle as a cross-section were differentiated to be 4 μm, 6 μm, and 8 μm and a charge rate (19.6%) of the patterns was uniformly maintained.

Based on light output, as a reference (100%), of the semiconductor light emitting device of Comparative example in which the micro-pattern (cylindrical shape) has a diameter of 6 μm, light outputs of Embodiments 1 to 3 and Comparative example are shown in the graph ofFIG. 7.

Referring toFIG. 7, it can be seen that Embodiments 1 to 3 having angled portions on the lateral portions has significantly improved light extraction efficiency relative to Comparative example in which the micro-pattern has a substantially cylindrical shape. In detail, although there are slight differences in terms of the enhancement of light extraction efficiency depending on the sizes of micro-patterns, it can be seen that light extraction efficiency was drastically improved in the case of the micro-pattern having the trigonal prism (Embodiment2) and the micro-pattern having a pillar structure having a plurality of tip portions (Embodiment 3).

In this manner, it is confirmed that, in the case of employing the angled portion in the lateral portion of the micro-pattern, as the internal angle of the angled portion is reduced, light extraction efficiency is further improved. Namely, as shown in the results of Embodiments 2 and 3, it can be understood that light extraction efficiency was drastically improved in the structure in which internal angles less than 60° had three or more shapes.

FIG. 8is a plan view of a semiconductor light emitting device according to another embodiment of the present invention.FIG. 9is a lateral-sectional view taken along line I-I′ of the semiconductor light emitting device illustrated inFIG. 8.

Referring toFIGS. 8 and 9, a semiconductor light emitting device70according to the present embodiment includes a semiconductor laminate75including first and second conductivity type semiconductor layers75aand75cand an active layer75bpositioned therebetween. The semiconductor laminate75has first and second main surfaces provided by the first and second conductivity type semiconductor layers75aand75cand positioned in the mutually opposite sides.

The semiconductor laminate75may be a group III-VI compound semiconductor such as a nitride semiconductor, but the present invention is not limited thereto. In the present embodiment, after a separate growth substrate is grown in order of the first conductivity type semiconductor layer75a, the active layer75b, and the second conductivity type semiconductor layer75cof the semiconductor laminate75, a wiring structure is formed on a first plane, and a support substrate71is employed.

Here, the support substrate71employed in the present embodiment may be a substrate having electrical conductivity. The support substrate71may be easily provided through a plating process. Subsequently, the growth substrate is removed from the semiconductor laminate75to obtain the device structure illustrated inFIG. 8. In a normal case, the first and second conductivity type semiconductor layers75aand75cmay be n-type and p-type semiconductor layers, respectively.

In the present embodiment, the configuration employing the support substrate is illustrated, but electrode structures may be formed without a support substrate (Please seeFIGS. 11 and 12).

In the present embodiment, a second electrode74may be formed on a second main surface of the semiconductor laminate75so as to be connected to the second conductivity type semiconductor layer75c. The second electrode74may be a highly reflective ohmic-contact layer reflecting light generated from the active layer75b. For example, the highly reflective ohmic-contact layer may be made of a material selected from the group consisting of silver (Ag), nickel (Ni), aluminum (Al), rhodium (Rh), palladium (Pd), iridium (Ir), ruthenium (Ru), magnesium (Mg), zinc (Zn), platinum (Pt), gold (Au), and any combination thereof.

A first electrode72connected to the first conductivity type semiconductor layer75ais provided on the second main surface of the semiconductor laminate75. As in the present embodiment, connection of the first electrode72and the first conductivity type semiconductor layer may be accomplished by using a contact hole H.

As illustrated inFIG. 9, at least one contact hole H may be formed in the semiconductor laminate75such that it extends by passing through the second conductivity type semiconductor layer75cand the active layer75buntil a portion of the first conductivity type semiconductor layer75ais exposed. The first conductivity type semiconductor layer75amay be exposed through the second main surface by the contact hole H formed thusly.

The first electrode72may be connected to the exposed region of the first conductivity type semiconductor layer75aprovided by the contact hole H, through an electrode region72′ extending from the first electrode72. Accordingly, the first electrode72positioned on the second main surface may be electrically connected to the first conductivity type semiconductor layer75a.

The contact hole H may be formed before a wiring structure is formed after the semiconductor laminate75is formed on a growth substrate. In the present embodiment, the contact hole H is illustrated as having the form of a via, but it may be variously implemented as long as a portion of the first conductivity type semiconductor layer75acan be exposed thereby.

In the present embodiment, as illustrated inFIG. 8, a plurality of contact holes H may be formed to be positioned over the entire effective light emitting area. Since the plurality of contact holes H are formed over the large area, a current may be uniformly distributed and the structure may be advantageously used in a semiconductor light emitting device having a large area for a high output.

An insulating separation layer73may be formed to easily electrically separate the first electrode72and the second electrode74provided on the main surface of the semiconductor laminate75. The insulating separation layer73may be formed to extend between an inner side wall of the contact hole H and the electrode region72′ of the first electrode72.

In the present embodiment, the support substrate71may be provided with the first and second electrodes72and74on the second main surface of the semiconductor laminate75, with a wiring structure comprised of the insulating separation layer73interposed therebetween.

The support substrate71employed in the present embodiment is a substrate having electrical conductivity. As illustrated inFIG. 9, the support substrate71is electrically separated from the second electrode74by the insulating separation layer73, and electrically connected to the first electrode72, and thus, the support substrate71may be provided as an electrode structure, for the first conductivity type semiconductor layer75a, together with the first electrode72. Namely, the conductive support substrate71may be connected together with an external circuit positioned on a mounting surface of the semiconductor light emitting device70.

In the present embodiment, a bonding region of one electrode of the semiconductor light emitting device70formed on an electrode pad79connected to the second electrode74may be provided on the first main surface opposite the second main surface. The semiconductor light emitting device70may further include a passivation layer (not shown) made of an insulating material formed at least on a lateral surface of the semiconductor laminate75.

FIG. 10Ais a cross-sectional view taken along line II-II′ of the semiconductor light emitting device70illustrated inFIG. 8andFIG. 10Bis a cross-sectional view taken along line III-III′.

Referring toFIG. 10A, the semiconductor light emitting device70is configured by sequentially stacking the first electrode72, the insulating separation layer73, the second electrode74, and the semiconductor laminate75on the support substrate71having electrical conductivity.

Meanwhile, referring toFIG. 10B, the semiconductor light emitting device70has a structure in which the first electrode72, the insulating separation layer73, the second electrode74, and the semiconductor laminate75are sequentially stacked on the support substrate71, similar to the stacked structure illustrated inFIG. 10A, except for regions in which holes are formed. Namely, the semiconductor light emitting device70has the structure in which the plurality of contact holes H connecting the first electrode72to the first75aare arranged at regular intervals. The plurality of contact holes H may reinforce uniform current distribution in the semiconductor light emitting device70.

In the present embodiment, a micro-pattern78may be formed on the first conductivity type semiconductor layer75aas a main light emitting surface of the semiconductor light emitting device70. The micro-pattern78has a section having four tip portions and has a pyramid structure.

Namely, the micro-pattern78employed on the present embodiment has a section having four sharp angled portions and an internal angle θ1of each of the angled portions toward the center of the micro-pattern78is less than 60°. Thus, since the tip portion having a sharp internal angle θ1 of less than 60° is formed on the lateral portion of the micro-pattern78, light extraction efficiency can be drastically increased.

FIG. 11is a schematic perspective view of a semiconductor light emitting device according to another embodiment of the present invention, andFIG. 12is a cross-sectional view of the semiconductor light emitting device illustrated inFIG. 11.

Referring toFIGS. 11 and 12, a semiconductor light emitting device100includes a semiconductor laminate105comprised of first and second conductivity type semiconductor layers105aand105cand an active layer105bpositioned therebetween.

The semiconductor laminate105has first and second main surfaces provided by the first and second conductivity type semiconductor layers105aand105cand positioned in the opposite sides. The semiconductor laminate105may be a group III-VI compound semiconductor such as a nitride semiconductor, but the present invention is not limited thereto.

In the present embodiment, unlike the embodiment illustrated inFIG. 11, a support substrate may not be employed and only an electrode structure may be formed.

A first electrode109aconnected to the first conductivity type semiconductor layer105ais provided on the second main surface of the semiconductor laminate105. Like the foregoing embodiment, the first electrode109aand the first conductivity type semiconductor layer105amay be connected by using a contact hole.

As illustrated inFIG. 12, at least one contact hole may be formed in the semiconductor laminate105such that it extends by passing through the second conductivity type semiconductor layer105cand the active layer105buntil a portion of the first conductivity type semiconductor layer105ais exposed. The first conductivity type semiconductor layer105amay be exposed through the second main surface by the contact hole formed thusly.

An ohmic-contact layer104may be formed on the second main surface of the semiconductor laminate105such that it is connected to the second conductivity type semiconductor layer105c. The ohmic-contact layer104is formed to reflect light generated from the active layer105b, and may be made of a material selected from the group consisting of silver (Ag), nickel (Ni), aluminum (Al), rhodium (Rh), palladium (Pd), iridium (Ir), ruthenium (Ru), magnesium (Mg), zinc (Zn), platinum (Pt), gold (Au), and any combination thereof. A second electrode109bmay be formed to be connected to the ohmic-contact layer104.

The first electrode109aprovided on the second main surface of the semiconductor laminate105is separated from the second electrode109b, and in order to guarantee electrical insulation between the ohmic-contact layer104and the first electrode109a, an insulating separation layer103may be formed between the ohmic-contact layer104and the first electrode109a. The insulating separation layer103may be formed to extend between an inner side wall of the contact hole and the first electrode109a.

In the present embodiment, a micro-pattern108may be formed on the first conductivity type semiconductor layer105aas a main light emitting surface of the semiconductor light emitting device100. The micro-pattern108has a pillar structure, and a section of the pillar structure is provided to be parallel to the light emitting surface and has a triangular shape.

As illustrated inFIG. 11, when viewed from above, the micro-pattern108has three angled portions. The provision of the angled portions formed on the lateral portions of the micro-pattern108may greatly contribute to effective extraction of light.

In addition, in order to further improve light extraction efficiency, the micro-pattern employed in the present embodiment may have a graded refractive index layer (GRIN) structure.

The GRIN structure has a refractive index distribution such that a refracted index is reduced as it moves away from the light emitting source, guaranteeing a smooth passage of light in a light emission direction. The GRIN structure may include at least two material layers having different refractive indices. In the present embodiment, the GRIN structure includes four material layers108ato108d.

In order to satisfy a refractive index condition of the micro-pattern108for light extraction, the respective material layers may be made of a material selected from the group consisting of TiO2, SiC, GaN, GaP, SiNx, ZrO2, ITO, AlN, Al2O3, MgO, SiO2, CaF2, and MgF2but the components thereof are not limited thereto. The respective material layers may be formed through a sputtering method or an evaporation method.

The GRIN structure may include a first material layer108ahaving a first refractive index and a second material layer108dhaving a second refractive index lower than the first refractive index, and may additionally include at least one third material layer108bformed between the first and second material layers108aand108dand having a refractive index between the first and second refractive indices. In the present embodiment, two third material layers108band108care included. The two third material layers108band108cmay be formed to be (composition of first material layer)1-x(composition of second material layer)x((0<x<1)), and a refractive index distribution may be gradually decreased between the first refractive index and the second refractive index from the first material layer108ato the second material layer108d.

For example, the two third material layers108band108cmay be formed to be (composition of first material layer)1-x(composition of second material layer)x((0<x<1)), and the x value may be increased from the first material layer108ato the second material layer108d.

For example, the first and second material layers108aand108dmay be TiO2and SiO2, and the third material layers108band108cmay be (TiO2)1-x(SiO2)x(0<x<1).

As discussed above, the two third material layers108band108cmay be (TiO2)1-x(SiO2)xor (ITO)1-x(SiO2)xin which the rate of the SiO2 material is gradually increased in a direction toward the second material layer108d.

In the present embodiment, a plurality of third material layers108band108care illustrated, but a single third material layer may be employed, and in this case, it may be formed such that (a composition of first material layer)1-x(a composition of second material layer)x((0<x<1)), thus implementing a middle refractive index.

The first refractive index of the first material layer108ais equal to or smaller than a refractive index of the material of the light emitting surface. For example, in the present embodiment, the first refractive index of the first material layer108amay be equal to or smaller than a refractive index of the first conductivity type semiconductor layer105a. A height and width of the micro-pattern108may range from 0.1 μm to 5 μm, but the present invention is not limited thereto. The micro-pattern108employed in the present embodiment may be formed by primarily taking a light extraction operation through lateral surfaces thereof into consideration.

As set forth above, according to embodiments of the invention, in a process of extracting light generated from the active layer of the semiconductor light emitting device, a light confinement phenomenon due to a difference between refractive indices of the semiconductor light emitting device and the atmosphere or an encapsulated material is reduced and light extraction efficiency is increased, thus enhancing luminous efficiency.