Semiconductor light emitting device and method of fabricating the same

Provided are a semiconductor light emitting device and a method of fabricating the same. The semiconductor light emitting device comprises a multireflection layer comprising at least one of reflection layers of different refractive indices, a first conductive semiconductor layer on the multireflection layers, an active layer on the first conductive type semiconductor layer, and a second conductive type semiconductor layer on the active layer.

TECHNICAL FIELD

Embodiments relate to a semiconductor light emitting device and a method of fabricating the same.

BACKGROUND ART

Groups III-V nitride semiconductors have been variously applied to an optical device such as blue and green light emitting diodes (LED), a high speed switching device, such as a MOSFET (Metal Semiconductor Field Effect Transistor) and an HEMT (Hetero junction Field Effect Transistors), and a light source of a lighting device or a display device.

The nitride semiconductor is mainly used for the LED (Light Emitting Diode) or an LD (laser diode), and studies have been continuously conducted to improve the manufacturing process or a light efficiency of the nitride semiconductor.

DISCLOSURE OF INVENTION

Technical Problem

Embodiments provide a semiconductor light emitting device capable of improving external quantum efficiency using a multi-reflection layer, and a method of fabricating the same.

Embodiments provide a semiconductor light emitting device comprising a multi-reflection layer comprising a plurality of reflection layers with different refractive indices which are disposed under a first conductive type semiconductor layer, and a method of fabricating the same.

Technical Solution

An embodiment provides a semiconductor light emitting device comprising: a multi-reflection layer comprising at least one of reflection layers with different refractive indices a first conductive semiconductor layer on the multi-reflection layers an active layer on the first conductive type semiconductor layer; and a second conductive type semiconductor layer on the active layer.

An embodiment provides a method of fabricating a semiconductor light emitting device comprising: forming a multi-reflection layer with an uneven structure on a substrate, the multi-reflection layer comprising reflection layers comprising different refractive indices; forming a first conductive type semiconductor layer on the substrate and the multi-reflection layer; forming an active layer on the first conductive type semiconductor layer; and forming a second conductive semiconductor layer on the active layer.

Advantageous Effects

Embodiments can improve the external quantum efficiency of a semiconductor light emitting device.

Also, embodiments can improve the crystallinity of a semiconductor thin film by means of a multi-reflection layer having an uneven structure.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. In the description, a thickness of each layer in the accompanying drawings is exemplarily illustrated, and thus not limited thereto.

FIG. 1is a side sectional view illustrating a semiconductor light emitting device100according to a first embodiment.

Referring toFIG. 1, the semiconductor light emitting device100comprises a substrate110, a multi-reflection layer120, a buffer layer130, an undoped semi-conductor layer140, a first conductive type semiconductor layer150, an active layer160, and a second conductive type semiconductor layer170.

The substrate110may comprise at least one of a sapphire (Al2O3) substrate, a silicon carbide (SiC) substrate, a silicon (Si) substrate, a gallium arsenide (GaAs) substrate, a gallium nitride (GaN) substrate, a zinc oxide (ZnO) substrate, a gallium phosphide (GaP) substrate, an indium phosphide (InP) substrate, and a germanium (Ge) substrate. Alternatively, the substrate110may comprise a conductive substrate. The surface of the substrate110may have an uneven pattern, however, it is not limited thereto. The substrate110may be removed according to a mounting method of a light emitting device.

A multi-reflection layer120having an uneven structure is formed on the substrate110. The multi-reflection layer120comprises a plurality of reflection layers121and122which are alternately stacked, and separated from each other by a predetermined distance. The multi-reflection layer120may be formed in a shape of a stripe or a lens, and may have a sectional shape of, for example, a hemisphere, a convex lens, a horn, or a polygon. However, the shape and section of the multi-reflection layer120may be variously modified within the scope of the embodiment.

The multi-reflection layer120comprises a pair of layers, e.g., the first and second reflection layers121and122having different refractive indices. Alternatively, the multi-reflection layer120may comprise a group of layers having 2-6 number of reflection layers. Further, the number of the first reflection layer121may be equal to or different from that of the second reflection layer122.

The multi-reflection layer120may comprise 2-50 number of pairs of the first and second reflection layers121and122. In the multi-reflection layer120, the first and second reflection layers121and122differ in diameter from each other. For instance, the diameter (or length) of the lowermost first reflection layer121may be greater than the diameter of the uppermost first reflection layer121. The diameter (or length) of the reflection layer121and122may gradually decrease from the bottom toward the top.

Each of the reflection layers121and122of the multi-reflection layer120are formed of at least one material of SiO2, Si3N4, SiON, TiO2, Al2O3, and ZrO. The first and second reflection layers121and122are formed of materials having different refractive indices.

The first reflection layer121may be formed of a material differing from a material used for the second reflection layer122, or formed of a material of which a refractive index differs from that of the second reflection layer122. For instance, a first refractive index of the first reflection layer121may be lower or higher than a second refractive index of the second reflection layer122. For example, the first and second reflection layers121and122may be formed of a pair of ZrO/SiO2layers. Herein, the refractive indices of the first and second reflection layers121and122may be lower than at least the refractive index of gallium nitride (GaN).

The refractive index of SiO2is 1.46, the refractive index of Si3N4is 2.05, the refractive index of SiON is 1.46-2.05, the refractive index of TiO2is 2.49-2.90, the refractive index of Al2O3is 1.77, and the refractive index of ZrO is 1.90.

The buffer layer130is formed on the substrate110and the multi-reflection layer120. The undoped semiconductor layer140may be formed on the buffer layer130. The buffer layer130functions to reduce a lattice constant difference from the substrate110, and may comprise a GaN buffer layer, an AlN buffer layer, an AlGaN buffer layer, an InGaN buffer layer, or the like. The buffer layer130may have an uneven surface. An undoped GaN layer may be used as the undoped semiconductor layer140. At least one of the buffer layer130and the undoped semiconductor layer140may be formed or none of them may be formed.

At least one first conductive type semiconductor layer150is formed on the undoped semiconductor layer140. An n-type semiconductor layer doped with n-type dopant may be used for the first conductive type semiconductor layer150. The n-type semi-conductor layer may be selected from GaN, AlGaN, InN, AlN, AlInN, InGaN, InAlGaN, and so forth. The n-type dopant may be selected from Si, Ge, Sn, Se, Te, etc.

The active layer160having a single or multi quantum well structure is formed on the first conductive semiconductor layer150. The active layer160comprises, for example, a quantum well layer formed of InGaN and a quantum barrier layer formed of GaN, which are alternately formed. Here, the quantum well layer has a composition of InxGa1-xN (0≦x≦1), however, is not limited thereto. The active layer160may change its light emitting wavelength and semiconductor material according to a light emitting material. Upon/under the active layer160, p-type/n-type clad layers may be formed.

At least one second conductive type semiconductor layer170is formed on the active layer160. A p-type semiconductor layer doped with p-type dopant may be used for the second conductive type semiconductor layer170. The p-type semiconductor layer may be selected from GaN, AlGaN, InN, AlN, AlInN, InGaN, InAlGaN, and so forth. The p-type dopant may be selected from Mg, Zn, Ca, Sr, Ba, etc.

A transparent electrode layer or/and a third conductive type semiconductor layer may be formed on the second conductive type semiconductor layer170. The third conductive semiconductor layer may be formed of an n-type semiconductor or a p-type semiconductor depending on an N-P-N junction structure or a P-N-P junction structure. A stack structure provided with the first conductive type semiconductor layer150, the active layer160and the second conductive type semiconductor layer170may be defined as a light emitting structure. The light emitting structure may have one of an N-P junction structure, an N-P-N junction structure, a P-N junction structure, and a P-N-P structure.

In the embodiment, the substrate110under the buffer layer130and the multi-reflection layer120may be removed through a laser lift off (LLO) method.

A first electrode layer171is formed on the first conductive type semiconductor layer150, and a second electrode layer173is formed on the second conductive type semi-conductor layer170.

The multi-reflection layer120reflects a portion of light, which is emitted from the active layer160and progresses toward the substrate110, by the use of the reflection layers121and122with different refractive indices, thus making it possible to improve light extraction efficiency and external quantum efficiency.

FIGS. 2 to 8are views illustrating a method of fabricating the semiconductor light emitting device according to the first embodiment.

Referring toFIGS. 2 and 3, reflection layers121and122with different refractive indices are alternately stacked on a substrate110. Here, the stacking of the reflection layers121and122may be performed by selectively using plasma vapor deposition (PVD) such as e-beam evaporation, thermal evaporation and magnetron sputtering (RF/DC sputtering), or chemical vapor deposition (CVD) such as plasma enhanced CVD (PECVD), low-pressure CVD (LPCVD) and atmospheric CVD (APCVD), however, the stacking of the reflection layers121and122is not limited thereto.

For example, the reflection layers121and122are alternately formed in such a way that the first reflection layer121of a first reflective material is formed, and the second reflection layer122of a second reflective material is then formed. Here, the first and second reflection layers121and122form one pair, and 2-50 pairs of reflection layers may be formed in total. The number of the first reflection layers121may be equal to or different from that of the second reflection layers122. Instead of one pair of the reflection layers, one group of 2-6 number of reflection layers may be used.

The first reflection layer121may be formed of a material of which a refractive index is higher or lower than that of a material used for the second reflection layer122. Each of the reflection layers121and122may be formed of at least one material of SiO2, Si3N4, SiON, TiO2, Al2O3, and ZrO. The first and second reflection layers121and122may be formed of different reflective materials or materials having different refractive indices. The refractive index of SiO2is 1.46, the refractive index of Si3N4is 2.05, the refractive index of SiON is 1.46-2.05, the refractive index of TiO2is 2.49-2.90, the refractive index of Al2O3is 1.77, and the refractive index of ZrO is 1.90. Here, the first and second reflection layers121and122may comprise a material of which a refractive index is lower than that of gallium nitride (GaN).

Referring toFIG. 4, photoresist patterns128are formed on the uppermost first reflection layer121of the reflection layers121and122. Here, the photoresist patterns128may be formed through photoresist coating process, soft baking process (e.g., heating at 90-190° C.), UV exposure process, developing process, and hard baking process (e.g., heating at 90-120° C.) in sequence. The photoresist patterns128are spaced apart from each other by a predetermined distance.

Referring toFIGS. 4 and 5, the photoresist pattern128may be changed into a hemi-spherical pattern128A through reflow baking process. Here, the reflow baking process may be performed at a temperature (e.g., 110-220° C.) higher than the temperature of the soft or hard baking process. Through the reflow baking process, the photoresist pattern128is changed into the hemispherical photoresist pattern128A. Factors determining the shape of the hemispherical photoresist pattern128A is a kind of the photoresist, reflow baking temperature, time, etc.

Referring toFIGS. 5 and 6, when the hemispherical photoresist pattern128A is formed on the reflection layers121and122, the reflection layers121and122are etched. The photoresist pattern128A is also etched when the reflection layers121and122are etched. Accordingly, patterns of the reflection layers121and122may be formed on the substrate110. A method of forming the multi-reflection layer120, i.e., the reflection layers121and122, by etching the photoresist pattern128A may be performed using, for example, a dry etching process using high-density plasma. Examples of available plasma may be inductively coupled plasma (ICP), capacitively coupled plasma (CCP), electron cyclotron resonance (ECR) plasma, microwave plasma, helicon, or the like. Although an available gas source may slightly differ according to a medium, chlorine-based gas (e.g., Cl2, BCl3), fluorine-based gas (e.g., CF4, SF6, NF3, C2F6), or inert gas (e.g., Ar, N2) may be used as the gas source.

Referring toFIG. 7, after the patterns of the multi-reflection layer120are formed on the substrate110, a buffer layer130is formed on the multi-reflection layer120, and an undoped semiconductor layer140is formed on the buffer layer130. Here, the surface of the buffer layer130may not be even, and the surface of the undoped semiconductor layer130may not be even. For planarization, a growth temperature and growth thickness can be adjusted.

The buffer layer130can relieve a lattice mismatch between a GaN material and a substrate material, and may be formed of at least one of GaN, AlGaN, InN, AlN, AlInN, InGaN and InAlGaN. The undoped semiconductor layer140may be formed of undoped GaN where conductive dopant is not added. The undoped semiconductor layer140serves as a substrate on which a nitride semiconductor grows. The buffer layer130and/or the undoped semiconductor layer140may not be formed, or may not exist in a final device.

A first conductive type semiconductor layer150is formed on the undoped semi-conductor layer140, an active layer160is formed on the first conductive type semi-conductor layer150, and a second conductive type semiconductor layer170is formed on the active layer160. Here, the first conductive type semiconductor layer150may comprise at least one of n-type semiconductor layers. The active layer160may have a single or multi quantum well structure. The second conductive type semiconductor layer170may comprise at least one of p-type semiconductor layers.

A transparent electrode layer (not shown) or/and a third conductive semiconductor layer may be formed on the second conductive type semiconductor layer170. The third conductive type semiconductor layer comprises an n-type semiconductor layer or a p-type semiconductor layer. Also, the substrate under the multi-reflection layer120may be removed through an LLO method.

Referring toFIG. 8, a portion of the first conductive type semiconductor layer150is exposed through mesa etching process. A first electrode layer171is formed on the first conductive type semiconductor layer150, and a second electrode layer173is formed on the second conductive type semiconductor layer170.

When a forward current is applied through the first and second electrode layers171and173, light is emitted from the active layer160. A portion of the light progressing toward the substrate110is reflected by the first reflection layer121or/and the second reflection layer122of the multi reflection layer120. The light reflected by the reflection layers121and122changes a critical angle, and thus is emitted to the outside.

The semiconductor light emitting device100reflects (i.e., scattered reflection) a portion of light using the multi-reflection layer120on the substrate110, thereby making it possible to improve light extraction efficiency and external quantum efficiency.

The semiconductor light emitting device of the embodiment can increase the crystallinity of a semiconductor thin film by disposing the multi-reflection layer with an uneven structure on the substrate.

FIG. 9is a side sectional view illustrating a semiconductor light emitting device according to a second embodiment.FIG. 10is an enlarged view of a portion A inFIG. 9.

Referring toFIGS. 9 and 10, the semiconductor light emitting device200comprises a multi-reflection layer220having an uneven surface on a substrate210.

The multi-reflection layer220may have a stack structure comprising first and second reflection layers221and222with different refractive indices. The first and second reflection layers221and222form a pair of reflection layers, and the multi-reflection layer220may comprise 2-50 number of pairs of reflection layers.

The multi-reflection layer220is formed in a stripe shape, of which a shape may be a polyprism (e.g., quadratic prism, hexagonal prism), or a polyhedron (e.g., tetrahedron).

Here, the first and second reflection layers221and222may be formed of at least one material of SiO2, Si3N4, SiON, TiO2, Al2O3, and ZrO, and the first and second reflection layers221and222may be formed of different materials or materials having different refractive indices. The refractive index of SiO2is 1.46, the refractive index of Si3N4is 2.05, the refractive index of SiON is 1.46-2.05, the refractive index of TiO2is 2.49-2.90, the refractive index of Al2O3is 1.77, and the refractive index of ZrO is 1.90. Herein, the first and second reflection layers221and222comprise materials having a refractive index lower than that of gallium nitride (GaN).

The multi-reflection layer220may be achieved by forming patterns of the multi-reflection layer220using a photoresist pattern. The detailed description for it has been made with reference to the first embodiment, and the multi-reflection layer220can be realized within the technical scope of the embodiment.

A buffer layer230, an undoped semiconductor layer240, a first conductive type semiconductor layer250, an active layer260, and a second conductive type semi-conductor layer270may be sequentially formed on the substrate210and the multi-reflection layer230. Here, the buffer layer230may be formed on the substrate210and the multi-reflection layer220, and the undoped semiconductor layer may be formed to a thickness ranging from 3 μm to 6 μm.

The thickness of each of the first and second reflection layers221and222, which are media with different refractive indices in the multi-reflection layer220, may be a quarter of the wavelength of the light emitting device. The thickness of each reflection layer can be calculated by following Equations:

where T represents the thickness of each medium, λ represents a wavelength of the light emitting device, and n represents a refractive index.

The semiconductor light emitting device200can reflect light, which is emitted from the active layer260and progresses toward the substrate110, by the multi-reflection layer220. The multi-reflection layer220reflects light progressing toward the substrate110using the first reflection layer221or the second reflection layer222, thereby changing a critical angle of the light. Accordingly, the light extraction efficiency and the external quantum efficiency of the semiconductor light emitting device200can be improved.

In the embodiment, the multi-reflection layer with the uneven surface is disposed on the substrate so that the crystallinity of the semiconductor thin film can be increased. In addition, it is possible to improve the external quantum efficiency using the scattered reflection of the multi-reflection layer.

The embodiment is also applicable to a semiconductor light emitting device having a horizontal or vertical electrode structure.

Hereinafter, a semiconductor light emitting device and a method of fabricating the same according to embodiments will be described in detail with reference to the accompanying drawings. In the description of embodiments, it will be understood that when a layer (or film), region, pattern or structure is referred to as being ‘on another layer (or film), region, pad or pattern, the terminology of ‘on’ and ‘under comprises both the meanings of ‘directly on/under and ‘indirectly on/under’. Further, the reference about ‘on and ‘under each layer will be made on the basis of drawings. Also, the thickness of each layer in the drawings is an example, and is not limited thereto.

INDUSTRIAL APPLICABILITY

The embodiment can provide a semiconductor light emitting device that can improve external quantum efficiency.

The embodiment can provide a semiconductor light emitting device that is variously applicable to a high-speed switching device, an illumination, or a light source of a display device.

The embodiment can provide a semiconductor light emitting device with enhanced reliability.