KR101360964B1

KR101360964B1 - Nitride semiconductor light emitting device and fabrication method thereof

Info

Publication number: KR101360964B1
Application number: KR1020070073883A
Authority: KR
Inventors: 정명구
Original assignee: 삼성전자주식회사
Priority date: 2007-07-24
Filing date: 2007-07-24
Publication date: 2014-02-11
Also published as: KR20090010622A

Abstract

The present invention relates to a nitride semiconductor light emitting device capable of improving light efficiency and minimizing a wavelength change according to an electric current, and a method of manufacturing the same. An n-type nitride semiconductor layer, a p-type nitride semiconductor layer, and the p-type nitride semiconductor layer and the A nitride semiconductor light emitting device comprising an active layer formed between an n-type nitride semiconductor layer and having a first quantum well layer and a first quantum barrier layer, wherein the second quantum well layer and the second quantum well layer are formed in the first quantum well layer. A nitride semiconductor light emitting device having a multi-quantum well structure composed of a barrier layer and a method of manufacturing the same are provided.

LED, nitride, GaN, light efficiency, piezoelectric field, wavelength change

Description

Nitride-based semiconductor light emitting device and its manufacturing method {NITRIDE SEMICONDUCTOR LIGHT EMITTING DEVICE AND FABRICATION METHOD THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor light emitting device, and more particularly, to a nitride semiconductor light emitting device capable of improving light efficiency and minimizing a change in wavelength according to a current and a method of manufacturing the same.

In general, nitride semiconductors are widely used in green or blue light emitting diodes (LEDs) or laser diodes (LDs), which are provided as light sources in full color displays, image scanners, various signal systems, and optical communication devices.

The nitride semiconductor light emitting device includes an active layer having a single quantum well (SQW) structure or a muti quantum well (MQW) structure disposed between n-type and p-type nitride semiconductor layers. Light is generated and emitted on the principle of recombination of electrons and holes.

The light efficiency of the nitride semiconductor light emitting device is determined by the probability of recombination of electrons and holes in the active layer, that is, the internal quantum efficiency. In order to improve the internal quantum efficiency, research has been conducted mainly to improve the structure of the active layer or to increase the effective mass of the carrier.

As a conventional scheme, the IEEE Electronic Device Paper (ELECTRON DEVICE LETTERS, Vol. 23, No. 3 March 2002, p130) has an electron asymmetric resonance tunneling structure consisting of an InGaN / GaN layer under an active layer which is a multi-quantum well structure. Tunneling structure has been proposed. According to this document, it is described that the luminous efficiency can be improved by reducing the operating current and voltage by introducing 50 nm of InGaN layer and 1 nm of GaN layer and injecting electrons accumulated in the InGaN layer into the active layer by tunneling principle. .

As described above, the InGaN layer and the GaN layer generally can effectively act as an electron emitting layer to increase the carrier capture probability in the active layer by increasing the effective amount of electrons lower than the effective amount of holes using the tunneling effect.

However, the solution still suffers from the problem that the recombination efficiency due to piezoelectric filed is reduced. That is, since the active layer having the multi-quantum well structure is formed by growing a plurality of quantum well layers and quantum barrier layers, which are nitride semiconductor layers, on the sapphire substrate, strain is generated due to the lattice constant difference.

In this way, the strain formed in the active layer acts as an important variable that determines the characteristics of the active layer, in particular, the distance between the wave function of electrons and holes in the active layer by causing a piezoelectric field due to strain in the active layer Since the distance from the light emitting recombination rate between the hole and the electron is lowered there is a problem that the light efficiency is lowered.

1 shows an energy band diagram of an active layer without strain applied, and FIGS. 2A and 2B show energy band diagrams of an active layer respectively with strain applied.

First, as shown in FIG. 1, when the strain does not act, the wave functions of electrons and holes in the quantum well layer are almost symmetrically distributed.

However, as shown in FIGS. 2A and 2B, when a strain of compressive or tensile stress acts due to lattice difference, a piezoelectric field is formed as indicated by an arrow due to the strain, thereby forming The distance between the wave functions of the holes increases.

As such, due to the increase in distance between the wave functions, there is a problem that the emitted light moves to a shorter wavelength as the current increases.

Therefore, even if the effective amount of the carrier is increased, the recombination probability does not increase substantially, and as a result, the luminous efficiency of the optical device is reduced.

Accordingly, the present invention has been made to solve the above problems, and an object of the present invention is to form a sub quantum well structure in the quantum well layer, thereby reducing the piezoelectric field, thereby minimizing the wavelength change according to the current, A nitride semiconductor light emitting device capable of improving light efficiency and a method of manufacturing the same are provided.

In order to achieve the above object, the present invention, the n-type nitride semiconductor layer, the p-type nitride semiconductor layer and the p-type nitride semiconductor layer and the n-type nitride semiconductor layer and formed between the first quantum well layer and the first quantum In a nitride semiconductor light emitting device including an active layer having a barrier layer, there is provided a nitride semiconductor light emitting device having a multi-quantum well structure including a plurality of second quantum well layers and a second quantum barrier layer in the first quantum well layer.

The second quantum well layer has a thickness of 1 ~ 100Å, the shape of the energy band gap of the quantum well structure and the sub quantum well structure is preferably one of the rectangular (rectangular), trapezoidal or triangular (triangular). .

The first quantum barrier layer or the second quantum barrier layer is formed of In _X Al _Y Ga ₁ -X _- _Y N (0≤X, 0≤Y, X + Y≤1), and the second quantum barrier layer The In content of the layer is higher than the In content of the first quantum barrier layer.

The first and second quantum well layers are formed of In _X Al _Y Ga ₁ -X _- _Y N (0≤X, 0≤Y, and X + Y≤1).

In addition, the present invention, n-type nitride semiconductor layer; p-type nitride semiconductor layer; An active layer having a quantum well structure between the p-type nitride semiconductor layer and the n-type nitride semiconductor layer; And a sub quantum well structure formed in the quantum well structure.

The quantum well structure and the sub quantum well structure, In _X Al _Y Ga ₁ _-X- _Y N (0≤X, 0≤Y, X + Y≤1), wherein the quantum well structure and sub The shape of the energy band gap of the quantum well structure may be one of a rectangular, trapezoidal, or triangular shape.

The sub quantum well structure is formed in the quantum well layer, and the In content of the sub quantum barrier layer with respect to the sub quantum well structure is preferably higher than the In content of the quantum barrier layer with respect to the quantum well structure. .

Alternatively, the thickness of the sub quantum well layer with respect to the sub quantum well structure is formed to 1 ~ 100Å.

In addition, the present invention, n-type nitride semiconductor layer; p-type nitride semiconductor layer; And an active layer having at least one first quantum well structure between the p-type nitride semiconductor layer and the n-type nitride semiconductor layer, and at least one second quantum well structure in the quantum well layer of the first quantum well structure. It provides a nitride semiconductor light emitting device having a.

The first and second quantum well structures include In _X Al _Y Ga ₁ _-X- _Y N (0≤X, 0≤Y, X + Y≤1), and a quantum barrier of the second quantum well structure The In content of the layer contains more than the In content of the quantum barrier layer of the first quantum well structure. The energy band gaps of the first and second quantum well structures may have one of a rectangular, trapezoidal, or triangular shape.

In this case, the thickness of the quantum well layer with respect to the second quantum well structure is preferably 1 ~ 100Å.

In addition, the present invention comprises the steps of preparing a substrate; Forming an n-type nitride semiconductor layer on the substrate; Forming an active layer having at least one quantum well structure on the n-type nitride semiconductor layer and having at least one sub quantum well structure in the quantum well layer of the quantum well structure; And it provides a method for producing a nitride semiconductor light emitting device comprising the step of forming a p-type nitride semiconductor layer on the active layer.

The quantum well structure and the sub quantum well structure may be formed by stacking at least _one quantum well structure including In _X Al _Y Ga ₁ _-X- _Y N (0≤X, 0≤Y, X + Y≤1). Can be.

The sub quantum well structure may be formed by adjusting the content of In, and the content of In may be controlled through a flow amount of an In source or by changing a growth temperature.

The quantum well layer of the sub quantum well structure is preferably formed to a thickness of 1 ~ 100Å.

As described above, the present invention provides a piezoelectric field by forming at least one sub quantum well structure in a quantum well layer of the quantum well structure in a nitride semiconductor light emitting device having an active layer composed of at least one quantum well structure. Reduction, thus minimizing the change of wavelength due to current.

That is, in the related art, a piezoelectric field due to strain in the active layer causes a distance between the electron and hole wave functions in the active layer, so that the emission light moves to a shorter wavelength as the current increases and the hole and the electron are increased. There was a problem in that the light emitting recombination rate with is lowered and the light efficiency is lowered.

Accordingly, the present invention forms at least one quantum well structure in the quantum well layer, so that the wave functions of electrons and holes in the quantum well layer are evenly distributed in the quantum well layer, thereby reducing the piezoelectric field due to strain in the active layer. As a result, not only the change of the wavelength due to the current is minimized, but also the light efficiency is improved by increasing the recombination rate between electrons and holes.

The nitride semiconductor light emitting device according to the present invention forms a multi-quantum well structure in the quantum well layer, thereby alleviating the piezoelectric field effect, minimizing the wavelength change caused by the increase of the current, and increasing the luminous efficiency, further improving the characteristics of the device. Can be improved.

Hereinafter, the nitride semiconductor light emitting device and the method of manufacturing the same according to the present invention will be described in detail with reference to the accompanying drawings.

3 schematically illustrates a cross-sectional structure of a nitride semiconductor light emitting device according to an example of the present invention.

As shown in the drawing, the nitride semiconductor light emitting device 100 according to the present invention includes an insulating substrate 110 and an n-type nitride semiconductor layer 120, an active layer 130, and p on the insulating substrate 110. It includes a light emitting structure 150 made of a type nitride semiconductor layer 140.

At this time, a layer for improving lattice matching between the insulating substrate 110 and the n-type nitride semiconductor layer 120 to be formed thereon between the insulating substrate 100 and the light emitting structure 150, a buffer layer (not shown) C) may be further included. The buffer layer is generally formed of undoped GaN or a nitride including Ga, for example, SiC / InGaN, which may be omitted depending on the type and growth method of the insulating substrate 110.

Partial regions of the p-type nitride semiconductor layer 140 and the active layer 130 are removed by a mesa etching process, thereby exposing a portion of the upper surface of the n-type nitride semiconductor layer 120, and the exposed n-type. The n-type electrode 170 is formed on the nitride semiconductor layer 120.

In addition, a transparent electrode 160 made of indium tin oxide (ITO) or the like is formed on the p-type nitride semiconductor layer 140, and a p-type electrode 180 is formed thereon.

The insulating substrate 110 is a substrate suitable for growing a nitride semiconductor single crystal, and is preferably formed using a transparent material including sapphire. In addition to sapphire, zinc oxide (ZnO), gallium nitride (GaN), gallium asenide (GaAs), silicon, silicon carbide (SiC) and aluminum nitride ( AlN) or the like.

The light emitting structure 150 is formed of a nitride semiconductor material having an In _X Al _Y Ga ₁ _-X- _Y N composition formula, where 0 ≦ X, 0 ≦ Y, and X + Y ≦ 1. In more detail, the n-type nitride semiconductor layer 120 may be formed of a GaN layer or a GaN / AlGaN layer doped with n-type impurities such as Si, Ge, Sn, and the like, and the p-type nitride semiconductor layer 140 It may be formed of a GaN layer or a GaN / AlGaN layer doped with p-type impurities such as silver, Mg, Zn, Be, or the like.

Meanwhile, the n-type nitride semiconductor layer 120 and the p-type nitride semiconductor layer 140 may include an n-type super lattice layer (not shown) and a p-type superlattice layer (not shown) to reduce lattice defects. Each may further include, and the superlattice layer has a structure in which at least three layers of Al x In y Ga z N (0 ≦ x, y, z ≦ 1) are repeatedly stacked, and preferably, AlGaN / GaN / InGaN. It may have a structure.

The active layer 130 may be composed of a multi-quantum well structure consisting of Al x In y Ga z N (0 ≦ x, y, z ≦ 1). For example, the InGaN-based quantum well layer 137 and the GaN-based quantum barrier layer ( 131 may be formed as a multi-quantum well structure having an alternately stacked structure. Alternatively, the active layer 130 may be formed of a single quantum well layer or a double-hetero structure, and the active layer 130 may have a height of a quantum barrier layer or a thickness, a composition, and a quantum well layer. By controlling the number of wells, you can control the wavelength or quantum efficiency.

However, in the present invention, in the quantum well layer 137 in the quantum well structure, there is another sub quantum well structure, wherein the sub quantum well structure is an InGaN-based sub quantum well layer 133 and a sub quantum barrier layer ( 135) has a multi-quantum well structure in which alternately stacked.

Here, the sub quantum well layer 133 is preferably designed to have a thickness in the range of 1 to 100 μs for the tunneling effect.

The sub quantum well layer 133 has the same energy band gap as that of the quantum well layer 137, and the sub quantum barrier layer 135 includes the quantum well layer 137 and the quantum barrier layer 131. Energy bandgap).

4 illustrates an energy band gap of an active layer for a nitride semiconductor light emitting device according to the present invention. In particular, an energy band gap of a sub quantum well structure in a quantum well layer is specifically illustrated.

As shown in the figure, the quantum well layer 137 of the active layer according to the present invention is lower than the energy band gap Eg (A) of the quantum barrier layer 131 formed on both sides of the quantum well layer 137. The sub quantum well layer 133 in the quantum well layer 137 has the same energy bandgap Eg (b) as the quantum well layer 137, and the sub quantum barrier layer 135 is the sub The energy band gap Eg (a) is higher than that of the quantum well layer 133 and lower than that of the quantum barrier layer 131.

In this case, the energy band gap shape of the quantum well structure or the sub quantum well structure may be one of a rectangular, trapezoidal, or triangular shape.

As described above, the quantum well layer has a multi-quantum well structure having a thin sub quantum well layer, wherein the sub quantum barrier layer 135 is higher than the quantum well layer 137 and the quantum barrier layer 131 By having an energy band gap lower than), the piezoelectric field due to the lattice constant difference can be alleviated.

This will be described in more detail, and due to the difference in lattice constant between the quantum barrier layer 131 and the quantum well layer 137, a piezoelectric field is generated, which increases as the thickness of the quantum well layer increases. Accordingly, the effect of the piezoelectric field is further increased. As a result, energy bend bending occurs, and electrons and holes in the quantum well layer move toward a lower energy level, and as shown in FIGS. 2A and 2B, the distance of the wave function of the hole is increased. The further the recombination rate is lowered.

Accordingly, in the present invention, a plurality of sub quantum barrier layers are disposed in the quantum well layer, and an energy band gap of the sub quantum barrier layer 135 is set to a value between the quantum well layer 137 and the quantum barrier layer 131. By growing a thin quantum well, the difference in energy band gap in the quantum well layer 137 is reduced, thereby alleviating the piezoelectric field. This is because the thickness of the sub quantum well layer 133 is smaller than that of the quantum well layer 137, so that the piezoelectric field is felt to be small, and thus the separation of the wave function formed in the sub quantum well structure is small. You lose.

As described above, the sub quantum well structure reduces the influence of the piezoelectric field effect to suppress an increase in the distance between the electron and hole wave functions, thereby reducing the width of the wavelength change due to the increase in the operating current, and reducing the recombination rate. It will raise the effect to increase the luminous efficiency.

As described above, in the present invention, the sub quantum well structure is configured in the quantum well layer to alleviate the piezoelectric field, and the sub quantum well structure controls the regular In content during growth of the quantum well layer 137. Can be formed through.

The In content may be adjusted by controlling the flow amount or growth temperature of the In source (trimethylindium (TMIn)). That is, adjustment of the In content is possible by gradually raising or lowering the In source or the growth temperature. In addition, the shape of the energy band gap of the quantum well structure varies according to the time of increasing and decreasing the flow amount or the deposition temperature of the In source.

5 and 6 show the In content according to the growth direction of the active layer (quantum barrier layer and sub quantum well structure), corresponding to the energy band gap shown in FIG.

As shown in the figure, as compared with the energy bandgap of Figure 4, it can be seen that the more the content of In decreases the energy bandgap.

Therefore, when the active layer grows, the In content of the quantum barrier layer 131 having the largest energy band gap is lowest, and the In content of the quantum well layer 137 and the sub quantum well layer 133 having the smallest energy band gap is The highest. The sub quantum barrier layer 135 in the quantum well layer 137 is higher than the quantum barrier layer 131 and has a lower In content than the quantum well layer 137. It is lower than the barrier layer and higher than the quantum well layer.

As described above, the In content can be controlled by changing the flow amount or growth temperature of the In source, the shorter the change time of the flow amount or growth temperature of the In source, as shown in FIG. The energy band gap is closer to the rectangular shape, and the longer the change time of these (the flow amount of the In source or the growth temperature), the closer the energy band gap is to the trapezoidal shape or the triangular shape as shown in FIG.

Therefore, in the present invention, the shape of the desired energy band gap can be determined by appropriately changing the flow amount or the deposition temperature of the In source.

As described above, the present invention forms a sub-quantum well structure in the quantum well layer of the active layer having the quantum well structure, thereby mitigating the piezoelectric field effect, minimizing the wavelength change and improving the light efficiency. An element and a method of manufacturing the same are provided.

That is, the nitride semiconductor light emitting device according to the present invention forms a sub quantum well structure having a sub quantum barrier layer having an energy band gap between the quantum well layer and the quantum barrier layer in the quantum well layer, By providing a relatively thin sub quantum well layer, the effect of the piezoelectric field is mitigated, and the sub quantum well structure is achieved by controlling the In content.

Accordingly, the basic concept of the present invention is to form a sub quantum well structure in a quantum well layer of the quantum well structure in a nitride semiconductor light emitting device in which the active layer has a quantum well structure in a nitride semiconductor light emitting device. In the example, in addition to the structure of the nitride semiconductor light emitting device presented, it may include all known nitride semiconductor light emitting devices including the basic concept of the present invention.

Accordingly, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concept of the present invention as defined in the following claims also belong to the scope of the present invention.

1 is an energy band diagram of an active layer when the piezoelectric field does not work.

2A and 2B are diagrams illustrating energy band diagrams of an active layer according to the action of a piezoelectric field of a conventional nitride semiconductor light emitting device.

3 is a cross-sectional view schematically showing a nitride semiconductor light emitting device according to the present invention.

4 is an energy band diagram of the active layer of FIG.

5 and 6 are views showing a change in the In content according to the growth direction of the active layer.

100 light emitting element 110 insulating substrate

120: n-type nitride semiconductor layer 130: active layer

131: quantum barrier layer 133: sub quantum well layer

135: sub quantum barrier layer 137: quantum well layer

140: p-type nitride semiconductor layer 150: light emitting structure

160: transparent electrode 170: n-type electrode

180: p-type electrode

Eg (A): energy bandgap of quantum barrier layer

Eg (a): energy band gap of sub quantum barrier layer

Eg (B): energy bandgap of quantum well layer

Eg (b): energy bandgap of sub quantum well layer

Claims

an n-type nitride semiconductor layer;

p-type nitride semiconductor layer; And

An active layer having at least one first quantum well structure between the p-type nitride semiconductor layer and the n-type nitride semiconductor layer,

The nitride semiconductor light emitting device having at least one second quantum well structure in the quantum well layer of the first quantum well structure, the thickness of the quantum well layer with respect to the second quantum well structure is 1 ~ 100Å.

The method of claim 1,

The first and second quantum well structures, In _X Al _Y Ga ₁ _-X- _Y N (0≤X, 0≤Y, X + Y≤1), characterized in that the nitride semiconductor light emitting device.

3. The method of claim 2,

A nitride semiconductor light emitting device, characterized in that the In content of the quantum barrier layer of the second quantum well structure is greater than the In content of the quantum barrier layer of the first quantum well structure.

The method of claim 1,

The energy band gap of the quantum barrier layer for the second quantum well structure is lower than the energy band gap of the quantum barrier layer for the first quantum well structure.

The method of claim 1,

The shape of the energy band gap of the first and second quantum well structure is one of rectangular, trapezoidal or triangular.

delete

Preparing a substrate;

Forming an n-type nitride semiconductor layer on the substrate;

Forming an active layer having at least one quantum well structure on the n-type nitride semiconductor layer and having at least one sub quantum well structure in the quantum well layer of the quantum well structure; And

Forming a p-type nitride semiconductor layer on the active layer;

And a quantum well layer of the sub quantum well structure having a thickness of 1 to 100 microns.

The method of claim 7, wherein

The quantum well structure and the sub quantum well structure may be formed by stacking at least _one quantum well structure including In _X Al _Y Ga ₁ _-X- _Y N (0≤X, 0≤Y, X + Y≤1). A method of manufacturing a nitride semiconductor light emitting device, characterized in that.

9. The method of claim 8,

The sub quantum well structure is a method of manufacturing a nitride semiconductor light emitting device, characterized in that formed by controlling the content of In.

10. The method of claim 9,

The content of In, the method of manufacturing a nitride semiconductor light emitting device, characterized in that by controlling the flow (flow) amount of In source.

10. The method of claim 9,

The content of In, the manufacturing method of the nitride semiconductor light emitting device, characterized in that by controlling the change in the growth temperature of InGaN.

delete