Nitride-based semiconductor light-emitting device

Abstract

The present invention relates to a nitride-based semiconductor light-emitting device comprising: a reflective film formed on a substrate and made of an amorphous distributed Bragg reflector (DBR) in which two or more materials having different refractive indices are alternately deposited; a non-conductive buffer layer formed using a sputter, to grow a nitride on the reflective film; a light-emitting structure including a non-conductive semiconductor layer, a first conductivity-type semiconductor layer, an active layer, and a second conductivity-type semiconductor layer sequentially stacked on the buffer layer; a transparent electrode layer sequentially stacked on the second conductivity-type semiconductor layer; and a metal electrode, wherein the device operates as a resonance cavity LED (RCLED) due to the reflectivity of the DBR in the reflective film formed in a lower layer and the reflectivity of the metal electrode formed in an upper layer.

Description

Nitride-based semiconductor light-emitting diode

[0001] The present invention relates to a technology for improving the luminous efficiency of a luminescent structure grown on a reflective film, and more specifically, to a nitride semiconductor light-emitting device configured such that the luminous efficiency of the nitride-based semiconductor light-emitting device grown on a reflective film is improved by the reflectivity of the reflective film.

[0002] Generally, a light-emitting diode (LED) is one of the light-emitting devices that emits light when current is applied.

[0003] Light-emitting diodes are known for their excellent energy-saving effects, as they emit high-efficiency light at low voltages.

[0004] Recently, the brightness of light-emitting diodes has been significantly improved, and they are being widely applied to various devices such as backlight units for display devices like LCDs, electronic billboards, indicators, and home appliances.

[0005] Light-emitting devices containing compounds such as AlGaInP, AlGaN, AlGaInN, AlGaAs, AlInGaAs, and InGaAsP have many advantages, such as having easily adjustable band gap energy, so they can be used in various ways as light-emitting devices, light-receiving devices, and various diodes.

[0006] In particular, light-emitting devices such as light-emitting diodes (LEDs) or laser diodes (LDs) using group 3-5 or group 2-6 compound semiconductor materials can produce various colors including near-infrared, red, green, blue, and ultraviolet light thanks to the development of thin-film growth technology and device materials.

[0007] Light-emitting devices that produce blue and ultraviolet light can also produce more efficient white light by using fluorescent materials or combining colors, and have advantages such as low power consumption, semi-permanent lifespan, fast response speed, safety, and environmental friendliness compared to conventional light sources such as fluorescent lamps and incandescent lamps.

[0008] Recently, active research and development is underway on technology to fabricate visible light-emitting diodes in micro-size and use them as pixels for high-resolution displays.

[0009] In addition, research and development on using visible light-emitting diodes for visible light communication has recently been actively underway, as well as on implementing light-emitting diodes on inexpensive amorphous substrates.

[0010] In particular, research and development on micro-sized light-emitting diodes is actively underway to secure high-speed modulation characteristics in visible light communication using nitride-based light-emitting diodes.

[0011] However, most nitride-based semiconductor light-emitting devices based on conventional technology have been grown on crystalline substrates. Although nitride-based light-emitting devices grown on amorphous substrates are also being studied, there are issues such as the complex manufacturing process and the need for further improvement in terms of light efficiency.

[0012] The objective of the present invention is to provide a nitride-based semiconductor light-emitting device in which an amorphous reflective film is deposited on a crystalline or amorphous substrate, and the luminous efficiency of a nitride-based light-emitting device grown on the upper surface of the reflective film is enhanced by the reflectivity of the reflective film.

[0013]

[0014] Another objective of the present invention is to provide a nitride-based semiconductor light-emitting device that increases light extraction efficiency by reducing the directional angle of light emitted from the light-emitting device.

[0015] A nitride-based semiconductor light-emitting device according to the present invention for achieving the above objective comprises: a reflective film formed on the upper surface of a substrate and composed of an amorphous dispersion Bragg reflector (DBR) in which two or more materials with different refractive indices are cross-deposited; a non-conductive buffer layer formed using sputtering to grow a nitride on the upper surface of the reflective film; a light-emitting structure composed of a non-conductive semiconductor layer, a first conductivity semiconductor layer, an active layer, and a second conductivity semiconductor layer sequentially stacked on the upper surface of the buffer layer; a transparent electrode layer sequentially stacked on the upper surface of the second conductivity semiconductor layer; and a metal electrode, wherein the device operates as a Resonance Cavity LED (RCLED) based on the reflectance of the DBR in the reflective film formed on the lower surface and the reflectance of the metal electrode formed on the upper surface.

[0016]

[0017] In addition, the directional angle of light emitted downward is reduced due to the overlap phenomenon between the wavelength of light generated in the active layer and the wavelength of the resonance cavity, and the selective reflection phenomenon according to the angle of incidence in the reflective film.

[0018]

[0019] In addition, the above-mentioned reflective film is composed of a combination of SiO2 / TiO2, and is characterized by having a reflectivity greater than 10% and less than 95%.

[0020]

[0021] In addition, the above-mentioned reflective film is composed of a combination of two or more oxide layers with different refractive indices among SiO2 / Ta2O5, Al2O3 / TiO2, and HfO2 / ZrO2 oxide layers, and the reflectivity of this combination is greater than 10% and less than 95%.

[0022]

[0023] In addition, the buffer layer is composed of an AIN layer or a GaN layer, and the AIN layer or GaN layer is formed on the upper surface of the reflective film using sputtering.

[0024]

[0025] In addition, the active layer comprises InGaN and is characterized by emitting blue light in the direction of the reflective film.

[0026]

[0027] In addition, the metal electrode is characterized by being made of a material having a reflectance of 50% or more.

[0028]

[0029] In addition, it is characterized in that the difference between the wavelength of the Fabry-Perot resonance formed by the above-mentioned reflective film and metal electrode and the wavelength of light emitted by the above-mentioned active layer is within ±10 nm.

[0030] The nitride-based semiconductor light-emitting device according to the present invention has the following effects.

[0031] First, an amorphous reflective film is deposited on a crystalline or amorphous substrate, and the luminous efficiency of a nitride-based light-emitting device grown on top of this reflective film is enhanced by the reflectivity of the reflective film.

[0032] Second, there is an effect of improving the internal quantum efficiency of the nitride light-emitting diode grown on top of the amorphous reflective film.

[0033] Third, depending on the difference between the wavelength of light generated in the active layer and the resonance wavelength formed by the resonance cavity, the directional angle of light emitted downward is reduced, thereby decreasing the amount of light lost inside the light-emitting device due to total reflection and increasing the light extraction efficiency emitted to the outside.

[0034] Fourth, as the directional angle of light emitted from the semiconductor light-emitting device decreases, the configuration of the optical system for efficiently utilizing this light from the outside becomes simpler, which has the effect of improving applicability.

[0035] FIG. 1 is a cross-sectional view showing the structure of a nitride-based semiconductor light-emitting device according to the present invention.

[0036] FIGS. 2 to 6 are cross-sectional views showing the manufacturing process of a nitride-based semiconductor light-emitting device according to the present invention.

[0037] Figure 7 is a graph showing the calculated reflectance values ​​according to the number of pairs and respective thicknesses of the reflective film according to the present invention.

[0038] Figure 8 is a graph showing the phenomenon in which the directional angle of light emitted from a nitride-based RCLED according to the present invention becomes narrower compared to the directional angle of a general LED.

[0039] Figure 9 is a graph showing the phenomenon in which the external quantum efficiency of a nitride-based semiconductor light-emitting device according to the present invention changes due to the lower DBR reflectance.

[0040] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, it should be noted that in assigning reference numerals to the components of each drawing, the same components are given the same reference numeral as much as possible, even if they are shown in different drawings.

[0041] In addition, in describing the present invention, detailed descriptions of related known components or functions are omitted if it is determined that such descriptions would be obvious to those skilled in the art or could obscure the essence of the invention.

[0042] FIG. 1 is a cross-sectional view showing the structure of a nitride-based semiconductor light-emitting device according to the present invention, FIG. 2 to 6 are cross-sectional views showing the manufacturing process of a nitride-based semiconductor light-emitting device according to the present invention, FIG. 7 is a graph showing the calculated values ​​of reflectance according to the number of pairs of reflective films and their respective thicknesses according to the present invention, FIG. 8 is a graph showing the phenomenon in which the directional angle of light emitted from a nitride-based RCLED according to the present invention becomes narrower compared to the directional angle of a general LED, and FIG. 9 is a graph showing the phenomenon in which the external quantum efficiency of a nitride-based semiconductor light-emitting device according to the present invention changes due to the lower DBR reflectance.

[0043] Referring to FIG. 1, the nitride-based semiconductor light-emitting device (100) according to the present invention comprises a reflective film (120), a buffer layer (130), a non-conductive semiconductor layer (140), a first conductive semiconductor layer (150), an active layer (160), a second conductive semiconductor layer (170), a transparent electrode layer (180), and an n-type metal electrode (190a) and a p-type metal electrode (190b) sequentially stacked on top of a substrate (110).

[0044] The nitride-based semiconductor light-emitting element according to the present invention configured as described above will be explained with reference to FIGS. 2 to 9 as follows.

[0045] As shown in FIG. 2, a reflective film (120) is formed on the upper surface of a substrate (110). The substrate (110) is made of a crystalline or amorphous material, and the reflective film (120) is made of an amorphous distributed Bragg reflector (DBR) in which two or more materials with different refractive indices, such as SiO2 / TiO2, are cross-deposited.

[0046] The substrate (110) may be composed of at least one of crystalline materials known to be suitable for semiconductor material growth, such as sapphire (Al2O3), SiC, Si, GaAs, GaN, ZnO, GaP, InP, Ge, Ga2O3, etc. Additionally, the substrate (110) may be composed of any material that maintains a stable state in the temperature or growth environment for depositing the light-emitting structure, regardless of characteristics such as amorphous or crystalline materials like glass or metal.

[0047] The above reflective film (120) is composed of a combination of SiO2 / TiO2, and its reflectivity is greater than 10% and less than 95%. As another example, the above reflective film (120) is composed of a combination of two or more oxide layers with different refractive indices, such as SiO2 / Ta2O5, Al2O3 / TiO2, HfO2 / ZrO2, and its reflectivity is greater than 10% and less than 95%.

[0048] The reflectivity of the above reflective film (120) can be adjusted according to the number of repetitions of the combination and the thickness of SiO2 / TiO2. A reflective film formed by cross-depositing two materials with different refractive indices with a thickness of λ / 4 within each material is called a DBR, and the thickness can be adjusted to obtain desired reflectivity characteristics through the reflective film (120).

[0049] Figure 7 shows the relationship between the reflectance of the reflective film (120) according to the wavelength of the DBR structure according to the number of repetitions of the TiO2 / SiO2 cross-layer and the thickness of each layer.

[0050] As shown in FIG. 7, a non-conductive buffer layer (130) is formed using sputtering to grow a nitride on the upper surface of the reflective film (120). The buffer layer (130) may be composed of an ANN layer or a GaN layer.

[0051] The above buffer layer (130) is an intermediate layer for forming a high-efficiency light-emitting structure (A) on top of the above reflective film (120). When the above buffer layer (130) is formed as an AlN layer or a GaN layer, its thickness may be between 10 nm and 300 nm.

[0052] A non-conductive semiconductor layer (140), which is a u-GaN sublayer that is not affected by the characteristics of the lower substrate depending on the thickness and formed shape of the above AIN layer or GaN layer, can be grown on the AIN layer or GaN layer with a composition formula of AlxGa1-xN (0≤x≤1) (see FIG. 8).

[0053] The above non-conductive semiconductor layer (140) may be formed from a semiconductor material having the composition formula InxAlyGa1-x-yN (0≤x≤1, 0 ≤y≤1, 0≤x+y≤1), and is not specifically limited thereto.

[0054] The above non-conductive semiconductor layer (140) is a u-GaN lower layer and has a significantly lower carrier concentration compared to the first and second conductive semiconductor layers (150, 170), for example, 10 16 cm -2 Since it has a carrier concentration below this level, no current actually flows.

[0055] Therefore, the above non-conductive semiconductor layer (140) serves to insulate the light-emitting structure (A).

[0056] As shown in FIG. 9, a light-emitting structure (A) is formed on top of a non-conductive semiconductor layer (140). The light-emitting structure (A) includes a first conductive semiconductor layer (150), an active layer (160), and a second conductive semiconductor layer (170) that are sequentially stacked.

[0057] The non-conductive semiconductor layer (140) and the light-emitting structure (A) can be formed using any one of the deposition technologies such as Metal Organic Chemical Vapor Deposition (MOCVD), Chemical Vapor Deposition (CVD), Plasma-Enhanced Chemical Vapor Deposition (PECVD), Molecular Beam Epitaxy (MBE), Hydride Vapor Phase Epitaxy (HVPE), Atomic Layer Deposition (ALD), and Sputtering.

[0058] A first conductive semiconductor layer (150) is formed on top of a non-conductive semiconductor layer (140), and then an active layer (160) is formed. The active layer (160) is a layer where electrons (or holes) injected through the first conductive semiconductor layer (150), which is an n-GaN layer, and holes (or electrons) injected through the second conductive semiconductor layer (170), which is a p-GaN layer, meet.

[0059] The active layer (160) includes InGaN and transitions to a lower energy level through the recombination of electrons and holes, and emits light having a corresponding wavelength (e.g., light in the blue wavelength range).

[0060] As shown in FIG. 6, the fabrication of a nitride-based semiconductor light-emitting device (100) is completed by sequentially stacking a reflective film (120), a buffer layer (130), a non-conductive semiconductor layer (140), a first conductive semiconductor layer (150), an active layer (160), a second conductive semiconductor layer (170), and a transparent electrode layer (180) on the upper part of a substrate (110), then etching so that one side of the first conductive semiconductor layer (150) is exposed to form an n-type metal electrode (190a) on the exposed portion, and forming a p-type metal electrode (190b) on the transparent electrode layer (180) on the unetched portion.

[0061] The light generated from the nitride-based semiconductor light-emitting device (100) produced in this way is emitted through the lower layer, a non-conductive semiconductor layer (140).

[0062] A nitride-based semiconductor light-emitting device (100) having a structure like that of Fig. 6 operates as an RCLED (Resonance Cavity LED) by the reflectance of the DBR in the reflective film (120) formed in the lower layer and the reflectance of the metal electrodes (190a) and (190b) formed in the upper layer.

[0063] Here, the metal electrodes (190a) and (190b) are preferably made of a material having a reflectance of 50% or more.

[0064] In addition, it is preferable that the difference in wavelength between the Fabry-Perot resonance formed by the reflective film (120) and the metal electrodes (190a), (190b) and the light emitted by the active layer (160) is within ±10 nm.

[0065] As shown in FIG. 8, the nitride-based semiconductor light-emitting device (100) has a beam angle of light emitted downwards that is reduced (narrowed) compared to a general LED due to the overlap phenomenon between the wavelength of light generated in the active layer (160) and the resonance cavity and the total reflection phenomenon in the reflective film (DBR) (120). When the beam angle of light emitted downwards is narrowed in this way, the amount of light lost inside the nitride-based semiconductor light-emitting device (100) due to total reflection is reduced.

[0066] Figure 9 shows the external quantum efficiency of the RCLED according to the change in reflectance of the reflective film (120).

[0067] As the reflectivity of the reflective film (120) increases, a resonant mode of the RCLED is formed, and spontaneous emission is enhanced due to the overlap between this resonant mode and the wavelength generated in the active layer (160). This enhancement phenomenon and the light direction angle reduction effect of FIG. 8 overlap, resulting in an increase in the external quantum efficiency of the RCLED.

[0068] On the other hand, if the reflectivity of the reflective film (120) increases further, the amount of light emitted to the outside decreases, and a phenomenon occurs in which the external quantum efficiency of the RCLED decreases.

[0069] Depending on the structure of the above RCLED, the optimal reflectance for the best external quantum efficiency may be changed.

Claims

1. A reflective film formed on the upper surface of a substrate and composed of an amorphous dispersed Bragg reflector (DBR) in which two or more materials with different refractive indices are cross-deposited; A non-conductive buffer layer formed using sputtering to grow a nitride on top of the above reflective film; A light-emitting structure comprising a non-conductive semiconductor layer, a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer sequentially stacked on top of the above buffer layer; A transparent electrode layer sequentially stacked on top of the above second conductivity type semiconductor layer; and Metal electrode; including, A nitride-based semiconductor light-emitting device that operates as an RCLED (Resonance Cavity LED) by means of the reflectance of the DBR in the reflective film formed in the lower layer and the reflectance of the metal electrode formed in the upper layer.

2. In Paragraph 1, A nitride-based semiconductor light-emitting device characterized by a reduction in the directional angle of light emitted downward due to the overlap phenomenon between the wavelength of light generated in the active layer and the wavelength of the resonance cavity, and the selective reflection phenomenon according to the angle of incidence in the reflective film.

3. In Paragraph 1, The above reflective film is A nitride-based semiconductor light-emitting device composed of a combination of SiO2 / TiO2, characterized in that its reflectivity is greater than 10% and less than 95%.

4. In Paragraph 1, The above reflective film is A nitride-based semiconductor light-emitting device characterized by being composed of a combination of two or more oxide layers with different refractive indices among SiO2 / Ta2O5, Al2O3 / TiO2, and HfO2 / ZrO2 oxide layers, wherein the reflectance of the combination is greater than 10% and less than 95%.

5. In Paragraph 1, The above buffer layer It consists of an ANN layer or a GaN layer, and A nitride-based semiconductor light-emitting device characterized in that the above-mentioned AIN layer or GaN layer is formed on the upper surface of the above-mentioned reflective film using sputtering.

6. In Paragraph 1, The above active layer A nitride-based semiconductor light-emitting device comprising InGaN and characterized by emitting light in the blue wavelength range in the direction of the reflective film.

7. In Paragraph 1, The above metal electrode is A nitride-based semiconductor light-emitting device characterized by being made of a material having a reflectance of 50% or more.

8. In Paragraph 1, A nitride-based semiconductor light-emitting device characterized by the difference between the wavelength of the Fabry-Perot resonance formed by the above-mentioned reflective film and metal electrode and the wavelength of light emitted by the above-mentioned active layer being within ±10 nm.

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