KR101502780B1 - High Efficiency Light Emitting Diode Epitaxial Structure - Google Patents

Abstract

In the present invention, instead of a p-GaN layer in contact with a metal electrode, an Al _x In _y Ga _{1 -xy} N (0? X? 1, 0? Y? 1 > layer to contact with the metal electrode to increase the amount of light transmitted through the layer in contact with the metal electrode without absorption of ultraviolet light, thereby improving the light extraction efficiency.

Description

[0001] The present invention relates to a high efficiency light emitting diode epitaxial structure,

The present invention relates to a high efficiency light emitting diode, and more particularly, to an epitaxial structure of an ultraviolet light emitting diode for improving light extraction efficiency.

In recent years, III-V nitride semiconductors such as GaN have attracted attention as core materials for semiconductor optical devices such as light emitting diodes (LEDs), laser diodes (LDs), and solar cells due to their excellent physical and chemical properties. The III-V group nitride semiconductors are usually made of a semiconductor material having a composition formula of Al _x In _y Ga _{1 -x- y} N (0? X? 1, 0? _Y? 1, 0? _X + y? Such nitride semiconductor optical devices are used as light sources for various products such as a backlight of a cellular phone, a keypad, a display board, and a lighting device.

Particularly, ultraviolet light emitting diodes are used in various fields such as semiconductor processing, sterilization, micro chemical detection, human genome analysis, and cardiac therapy, and Korean Patent Laid-Open No. 10-2007-0008995 using GaN etc. also discloses an ultraviolet light emitting diode However, there is a problem that the efficiency is limited because the light can not be efficiently extracted.

FIG. 1 is a view for explaining the structure of a conventional ultraviolet light-emitting diode 100. FIG. Figure 2 is an energy band diagram for the structure of Figure 1;

1, a conventional ultraviolet light-emitting diode 100 is formed by forming a template layer 120 of GaN or the like on a substrate 110 and then forming an n-GaN layer 131 as a light emitting diode (LED) an active layer (MQW) (132), and a structure is formed in the electron blocking layer (EBL) (133), p ⁺ -AlGaN layer (134), p ⁺ -GaN layer 135. Here, a predetermined electric power is applied to the metal electrode 142 which is in contact with the n-GaN layer 131 and the metal electrode 142 which is in contact with the p ⁺ -GaN layer 135 to form the light emitting diode (LED) So that ultraviolet rays can be generated.

However, such a conventional UV light emitting diode (100) structure, by the p ⁺ -AlGaN layer 134 because of the high activation energy as well as a low concentration of holes, an electron blocking layer (EBL) (133) in the p ⁺ -AlGaN layer 134, and thus the hole injection efficiency into the active layer (MQW) 132 is lowered and the light extraction efficiency is lowered. In addition, the large bandgap of the p ⁺ -AlGaN layer 134 requires a large activation energy in the doping of Mg or the like, which causes a problem that the doping is not performed well, and the p ⁺ -AlGaN layer 134 ) and a metal electrode are O-mixer (ohmic) contact because the problem is difficult to, but p ⁺ -GaN layer 135 is formed for the O-dynamic contact with a metal electrode (142), p ⁺ -GaN layer ( The band gap energy of the p ⁺ -GaN layer 135 becomes smaller than the ultraviolet energy (about 3.5 eV), so that ultraviolet rays are absorbed in the p ⁺ -GaN layer 135 and the amount of ultraviolet rays emitted is decreased.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide an Al _x In _y Ga _{1 -xy} N (AlGaN) 1, 0 < y &lt; 1, 0 &lt; x + y &lt; 1) layer to contact the metal electrode to increase the transmittance without ultraviolet absorption in the layer in contact with the metal electrode, Thereby providing an epitaxial structure of the diode.

First, a summary of the features of the present invention, the ultraviolet light-emitting diode according to one aspect of the present invention for achieving the object of the present invention as described above, are sequentially laminated between the two electrodes for applying a voltage, Al _x In _y Ga _{1 -x- y n (0≤x≤1, 0≤y≤1} , 0≤x + y≤1) nitride n-type nitride layer and an active layer made of, and _{Al x in y Ga 1 -xy n} (0≤ x≤1, 0≤y≤1, 0 <x + y≤1) to include a p-type nitride layer and an n-type impurity concentration is higher than the n ⁺ layer made of a nitride, it said active layer is a barrier layer and quantum well Layer is repeatedly formed at least once, and the p-type nitride layer is a concentration gradient layer such that Al or In concentration gradually decreases in the laminating direction.

The bandgap energy of the n ⁺ -type nitride layer is maintained to be greater than the energy of ultraviolet rays generated in the active layer, thereby enhancing the emission effect of the ultraviolet rays to the outside.

The p-type nitride layer blocks electron injection from the active layer and provides hole injection into the active layer.

And a flattened valence band formed by forming a hole gas in accordance with the electric field induction by a polarization effect in accordance with the concentration gradient in the p-type nitride layer.

Each of the sequentially stacked layers may be formed in situ in a reactor of a hydride vapor phase epitaxy (HVPE) or metal-organic chemical vapor deposition (MOCVD) equipment.

According to another aspect of the present invention, there is provided a method of manufacturing an ultraviolet light-emitting diode, the method comprising: forming an Al _x In _y Ga _{1 -x- y} N (0 x 1, 0 _y 1, 0 x + 1) n-type nitride layer and an active layer, and a p-type nitride layer made of Al _x In _y Ga _{1 -xy} N (0? X? 1, 0? _Y? 1, 0 <x + And an n ⁺ -type nitride layer having a higher impurity concentration than the n-type layer, wherein the barrier layer and the quantum well layer are repeatedly formed as the active layer, and at the time of forming the p-type nitride layer, And is formed of a gradient layer so that the Al or In concentration gradually decreases.

According to the epitaxial structure of the ultraviolet light emitting diode according to the present invention, Al _x In _y Ga _{1 -xy} N (0? X? 1, 0? _Y? 1, 0 <x + y? Layer in contact with the metal electrode while increasing the transmittance without ultraviolet absorption in the layer in contact with the metal electrode, thereby improving the light extraction efficiency.

In addition, the efficiency of injecting holes into the active layer (MQW) is increased while maintaining a high hole concentration in the layer in contact with the metal electrode, thereby providing ultraviolet rays having high emission intensity.

FIG. 1 is a view for explaining the structure of a conventional ultraviolet light-emitting diode 100. FIG.
Figure 2 is an energy band diagram for the structure of Figure 1;
3 is a cross-sectional view illustrating an epitaxial structure of an ultraviolet light-emitting diode according to an embodiment of the present invention.
Figure 4 is an energy band diagram for the structure of Figure 3;
FIG. 5 is a graph comparing the light emission intensity of the conventional structure and the structure of the present invention.
6 is a graph showing the electron and hole concentration of each layer in the conventional structure.
7 is a graph showing the electron and hole concentration of each layer in the structure of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout.

3 is a cross-sectional view illustrating an epitaxial structure of an ultraviolet light emitting diode 200 according to an embodiment of the present invention. Figure 4 is an energy band diagram for the structure of Figure 3;

3, the ultraviolet light-emitting diode 200 according to one embodiment of the present invention, for applying a voltage are sequentially laminated between the two electrodes _{(241, 242), Al x} In y Ga 1 -x- y An n-type nitride layer 231 (for example, n / n ⁺ -AlGaN) made of nitride of N (0? X? 1, 0? Y? 1, 0? X ⁺ ) 232 and a p-type nitride layer 233 (e.g., p ⁺ -type) made of Al _x In _y Ga _{1 -xy} N (0? X? 1, 0? Y? -AlGaN), and an n ⁺ -type nitride layer 234 (e.g., n ⁺ -AlGaN) having a higher impurity concentration than the n-type.

Each of the sequentially deposited layers 231 to 234 is deposited on a bare substrate such as a sapphire substrate, a SiC substrate, or an Si substrate in a reactor of a hydride vapor phase epitaxy (HVPE) or metal-organic chemical vapor deposition _x Al _y Ga _{1 -x- y} N (0? x? 1, 0? y? 1, 0? x + y? 1), and then a template layer or buffer layer made of In- ).

The active layer 232 may be made of a nitride of Al _x In _y Ga _{1 -x- y} N (0? X? 1, 0? _Y? 1, 0? X + y? 1) (For example, GaN) and a quantum well layer (e.g., In _0.15 Ga _{0.8 5} N) is repeatedly formed one or more times to a thickness of several nanometers to form a barrier layer (For example, GaN) and a quantum well layer (eg, In _0.15 Ga _0.85 N) are formed so that the electrons trapped in the conduction band of the quantum well layer (eg, In _{0 .15} Ga _{0 .85} N) band to recombine with the holes of the light emitting layer to emit necessary ultraviolet rays.

Unlike the n-type nitride layer 231 and the active layer 232 made of nitride of Al _x In _y Ga _{1 -x- y} N (0? X? 1, 0? _Y? 1, 0? _X + y? 1) p-type nitride layer 233 (for example, p ⁺ -AlGaN), and the impurity than the n-type (for example, Si, etc.) concentration of high n ⁺ -type nitride layer 234 (for example, n ⁺ -AlGaN) is Al _x In _y Ga _{1 -xy} N (0? x? 1, 0? y? 1, 0 <x + y? 1). In other words, it is made of a layer in which impurities such as Al and In are mixed in addition to GaN. The p-type nitride layer 233 may be doped with a suitable impurity to form a p-type semiconductor such as Mg.

According to such a structure, Al _x In _y Ga _{1 -xy} N (0? X? 1, 0? Y? 1, 0 < x + y (For example, x and y are selected so that the band gap energy of the n ⁺ type nitride layer 234 is 5 eV or more) is easily transmitted and emitted to the outside, thereby increasing the light extraction efficiency .

In order to facilitate easy ohmic contact with the metal electrode 242 by the n ⁺ -type nitride layer 234 (e.g., n ⁺ -AlGaN) in this structure, a p-type nitride layer 233) (for example, p ⁺ -AlGaN) may be formed as a gradient layer such that the Al or In concentration is gradually decreased in the laminating direction so that the conduction band is gradually lowered in the laminating direction, An n ⁺ -type nitride layer 234 (e.g., n ⁺ -AlGaN) is deposited in sequence.

Accordingly, the n ⁺ -type nitride layer 234 (e.g., n ⁺ -AlGaN) corresponding to the n-type semiconductor layer is brought into contact with the p-type nitride layer 233 (e.g., p ⁺ -AlGaN) so that it interferes with the energy band n ⁺ type nitride layer 234 (for example, n ⁺ -AlGaN) inclined gently from the n ⁺ type nitride layer 234 can be a dynamic ohoh contact (for example, n ⁺ -AlGaN) The material of the metal electrode 242 (e.g., Ti, Al, Ni, Au, Ag, Pt, Cr, Cu, Rh, or an alloy thereof) can be easily selected.

That is, the conduction band and valence band levels from the p-type nitride layer 233 (eg, p ⁺ -AlGaN) to the n ⁺ -type nitride layer 234 (eg, n ⁺ -AlGaN) Electrons migrate from the p-type nitride layer 233 (e.g., p ⁺ -AlGaN) to the n ⁺ type nitride layer 234 (e.g., n ⁺ -AlGaN) and the n ⁺ type nitride layer 234 (E.g., n ⁺ -AlGaN) to the p-type nitride layer 233 (e.g., p ⁺ -AlGaN) can be easily performed. The p-type nitride layer 233 (for example, p ⁺ -AlGaN) serves as an electron blocking layer (EBL) for blocking electron injection from the active layer 232 and provides hole injection into the active layer 232, a high concentration hole (see FIG. 7) introduced from the n ⁺ -type nitride layer 234 (for example, n ⁺ -AlGaN) is formed on the valence band side of the existing electron blocking layer (EBL) The hole injection efficiency into the active layer 232 can be enhanced by utilizing a flattened valence band without a hole barrier. Accordingly, it is possible to expect light extraction of ultraviolet rays having high emission intensity.

Particularly, when the p-type nitride layer 233 (for example, p ⁺ -AlGaN) is formed in a concentration gradient layer such that Al or In concentration is gradually decreased in the laminating direction, And lowering it at a certain rate according to time. This results in a polarization effect depending on the gradient of the Al or In concentration in the p-type nitride layer 233 (e.g., p ⁺ -AlGaN) to induce an electric field by a dipole of atoms or molecules the energy level of the conduction band is gradually lowered as shown in FIG. 4, but the energy level of the valence band is maintained to be flattened in the direction of the stacking The hole injection efficiency into the active layer 232 can be increased.

As a result of the simulation, it is confirmed that the light emission intensity 520 in the structure of the present invention as shown in FIG. 3 is higher than the light emission intensity 510 of the conventional structure having EBL (see FIG. 1) Respectively. In addition, it has been confirmed that the operating voltage ( _Vf ) becomes lower in the structure of the present invention than in the conventional structure (see FIG. 1).

6, the concentration of holes injected into the active layer is about 10 ¹⁷ / cm ^{3 in the} conventional structure (see FIG. 1). However, in the structure of the present invention, the p-type nitride layer 233 p ⁺ -AlGaN) to the active layer 232 is improved to about 10 ¹⁸ / cm ³ .

Thus, in the epitaxial structure of the ultraviolet light emitting diode of the present invention, Al _x In _y Ga _{1 -xy} N (0? X? 1, 0? _Y? 1, 0 <x + It is possible to improve the light extraction efficiency by increasing the amount of transmission without ultraviolet absorption in a layer in contact with the metal electrode 242 while being in an ohmic contact with the metal electrode 242.

While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. This is possible. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined by the equivalents of the claims, as well as the claims.

Claims (6)

Type nitride layer made of Al _x In _y Ga _1-xy N (0? X? 1, 0? _Y? 1, 0? _X + y? 1) nitride sequentially stacked between two electrodes for applying a voltage And an active layer and a p-type nitride layer made of Al _x In _y Ga _1-xy N (0? X? 1, 0? _Y? 1, 0 <x + y? 1) ⁺ Type nitride layer,
A barrier layer and a quantum well layer are formed on the active layer at least once,
In the p-type nitride layer, holes are formed by polarization along a concentration gradient in which Al or In concentration is continuously decreased in the laminating direction,
And the band gap energy of the n ⁺ -type nitride layer is greater than the energy of ultraviolet light generated in the active layer. delete The method according to claim 1,
Wherein the p-type nitride layer interrupts electron injection from the active layer and provides hole injection into the active layer. The method of claim 3,
And a flattened valence band formed by forming a hole gas according to an electric field induction by a polarization effect according to a concentration gradient in the p-type nitride layer. The method according to claim 1,
Wherein each of the sequentially stacked layers is formed in situ in a reactor of a hydride vapor phase epitaxy (HVPE) or metal-organic chemical vapor deposition (MOCVD) equipment. Substrate onto the _{Al x In y Ga 1-xy} N (0≤x≤1, 0≤y≤1, 0≤x + y≤1) n -type nitride layer and an active layer of a nitride, and Al _x In _y Ga ₁ a step of sequentially laminating a p-type nitride layer made of _-xy N (0? x? 1, 0? y? 1, 0 <x + y? 1) and an n ⁺ type nitride layer having a higher impurity concentration than n- &Lt; / RTI &
A barrier layer and a quantum well layer are formed on the active layer one or more times,
In the p-type nitride layer, holes are formed by polarization along a concentration gradient in which Al or In concentration is continuously decreased in the laminating direction,
Wherein the band gap energy of the n ⁺ type nitride layer is maintained to be greater than the energy of ultraviolet light generated in the active layer.

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