KR20080088221A - Light emitting diode having well layer of superlattice structure - Google Patents

Abstract

A light emitting diode having a well layer of a super lattice structure is provided to improve optical efficiency by reducing generation of crystalline defects. A light emitting diode includes an active region between a gallium nitride-based N type compound semiconductor layer(57) and a gallium nitride-based P type compound semiconductor layer(61). The active region includes a well layer(59a) and a barrier layer(59b) of a super lattice structure. The well layer of the super lattice structure is a super lattice structure including a stacked structure of InN and GaN. The barrier layer is formed with GaN. The well layer is a super lattice structure as a stacked structure of InxGa1-xN and InyGa1-yN.

Description

LIGHT EMITTING DIODE HAVING WELL LAYER OF SUPERLATTICE STRUCTURE}

1 is a cross-sectional view illustrating a conventional light emitting diode.

2 is a cross-sectional view illustrating a light emitting diode having a well layer of a superlattice structure according to an exemplary embodiment of the present invention.

3 is a cross-sectional view illustrating a well layer of a superlattice structure according to embodiments of the present invention.

4 is a cross-sectional view for describing a light emitting diode according to another exemplary embodiment of the present invention.

The present invention relates to a light emitting diode, and more particularly, to a light emitting diode having a well layer having a superlattice structure.

In general, nitrides of Group III elements such as gallium nitride (GaN), aluminum nitride (AlN), and indium gallium nitride (InGaN) have excellent thermal stability and have a direct transition energy band structure. It is attracting much attention as a material for light emitting diodes in the ultraviolet region. In particular, indium gallium nitride (InGaN) compound semiconductors have attracted much attention due to their narrow band gap. Light emitting diodes using gallium nitride-based compound semiconductors are being used in various applications such as large-scale color flat panel display devices, backlight light sources, traffic lights, indoor lighting, high density light sources, high resolution output systems, and optical communications. In addition, light emitting diodes emitting near ultraviolet rays are used for gastric sensitization, resin curing, and ultraviolet light treatment, and may also be combined with phosphors to implement visible light of various colors.

1 is a cross-sectional view illustrating a conventional light emitting diode.

Referring to FIG. 1, the light emitting diode includes an N-type semiconductor layer 17 and a P-type semiconductor layer 21, and an active region 19 is formed between the N-type and P-type semiconductor layers 17 and 21. It is interposed. The N-type semiconductor layer and the P-type semiconductor layer are formed of a nitride semiconductor layer of a group III element, that is, a compound semiconductor layer of (Al, In, Ga) N series. On the other hand, the active region 19 is a single quantum well structure having one well layer, or as shown, is formed in a multi quantum well structure having a plurality of well layers. The active region of the multi-quantum well structure is formed by alternately stacking an InGaN well layer 19a and a GaN barrier layer 19b. The well layer 19a is formed of a semiconductor layer having a smaller bandgap than the N-type and P-type semiconductor layers 17 and 19 and the barrier layer 19b to provide a quantum well in which electrons and holes are recombined.

The nitride semiconductor layer of the group III element is grown through a process such as metal organic chemical vapor deposition (MOCVD) on a heterogeneous substrate 11 such as sapphire or silicon carbide (SiC) having a hexagonal structure. However, when a nitride semiconductor layer of a group III element is formed on the hetero substrate 11, cracks or warpages are caused in the semiconductor layer due to the difference in lattice constant and thermal expansion coefficient between the semiconductor layer and the substrate. Occurs, and a dislocation is generated.

In order to prevent this, a buffer layer is formed on the substrate 11, and generally, a low temperature buffer layer 13 and a high temperature buffer layer 15 are formed. The low temperature buffer layer 13 is generally formed of Al _x Ga _{1 - x} N (0 ≦ _x ≦ 1) at a temperature of 400 ° C. to 800 ° C. using a MOCVD process or the like. Subsequently, the high temperature buffer layer 15 is formed on the low temperature buffer layer 13. The high temperature buffer layer 15 is formed of a GaN layer at a temperature of 900 ~ 1200 ℃. As a result, crystal defects of the N-type GaN layer 17, the active region 19, and the P-type GaN layer 21 can be significantly removed.

However, despite the adoption of the buffer layers 13 and 15, the crystal defect density in the active region 19 is still high. In particular, the active region 19 is formed of a semiconductor layer having a smaller band gap than the N-type GaN layer 17 and the P-type GaN layer 19 in order to increase the coupling efficiency between electrons and holes, and also the well layer 19a. ) Is formed of a semiconductor layer with a smaller bandgap than the GaN barrier layer 19b, and generally contains a large amount of In. Since In is relatively larger than Ga, the lattice constant of the well layer is relatively large compared to the lattice constant of the barrier layer. Accordingly, lattice mismatch occurs between the well layer 19a and the barrier layer 19b and between the well layer 19a and the N-type semiconductor layer 17, and the lattice mismatch between these layers reduces the crystallinity of the well layer. Limit light efficiency

An object of the present invention is to provide a light emitting diode capable of reducing the occurrence of crystal defects due to lattice mismatch between the well layer and the barrier layer in the active region.

In order to achieve the above technical problem, the present invention provides a light emitting diode having a well layer having a superlattice structure. A light emitting diode according to an aspect of the present invention is a light emitting diode having an active region between a gallium nitride series N-type compound semiconductor layer and a gallium nitride series P-type compound semiconductor layer, the well layer having a superlattice structure in the active region. And a barrier layer. By adopting the well layer of the superlattice structure, it is possible to reduce the occurrence of defects due to lattice mismatch between the well layer and the barrier layer.

The well layer of the superlattice structure may be a superlattice structure formed by alternately growing InN and GaN, and the barrier layer may be formed of GaN. The well layer In composition may be adjusted to implement light in an ultraviolet or visible light region.

The well layer may have a superlattice structure in which In _x Ga _{1 - x} N and In _y Ga _{1 - y} N are alternately stacked, where 0 ≦ x, y ≦ 1, and x> y.

On the other hand, the barrier layer may also be a superlattice structure. Accordingly, the occurrence of defects due to lattice mismatch between the well layer and the barrier layer can be further reduced.

The barrier layer of the superlattice structure may be a superlattice structure formed by alternately growing InN and GaN. Further, the barrier layers of said superlattice structure is In _u Ga _{1 -u} N and In _v Ga _{1 - v} and N may be a superlattice structure are alternately laminated by, where, 0≤u, v≤1, u> v.

The In _v Ga _{1 - v} N has a larger band gap than the well layer of the superlattice structure. For example, In _v Ga _{1 - v} N contains less In as compared to In _x Ga _{1 - x} N in the well layer.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided as examples to ensure that the spirit of the present invention can be fully conveyed to those skilled in the art. Accordingly, the present invention is not limited to the embodiments described below and may be embodied in other forms. And, in the drawings, the width, length, thickness, etc. of the components may be exaggerated for convenience. Like numbers refer to like elements throughout.

2 is a cross-sectional view illustrating a light emitting diode according to an embodiment of the present invention.

Referring to FIG. 2, an N-type compound semiconductor layer 57 is positioned on the substrate 51. In addition, a buffer layer may be interposed between the substrate 51 and the N-type compound semiconductor layer 57, and the buffer layer may include a low temperature buffer layer 53 and a high temperature buffer layer 55. The substrate 51 is not particularly limited and may be, for example, sapphire, spinel, silicon carbide substrate, or the like. Meanwhile, the low temperature buffer layer 53 may be generally formed of Al _x Ga _{1 - x} N (0 ≦ _x ≦ 1), and the high temperature buffer layer 55 may be, for example, an n type doped with undoped GaN or n type impurities. GaN.

A P-type compound semiconductor layer 61 is positioned on the N-type compound semiconductor layer 57, and an active region 59 is interposed between the N-type compound semiconductor layer 57 and the P-type compound semiconductor layer 61. . The N-type compound semiconductor layer and the P-type compound semiconductor layer may be formed of a group III nitride semiconductor layer of (Al, In, Ga) N series. For example, the N-type compound semiconductor layer 57 and the P-type compound semiconductor layer 61 may be N-type and P-type GaN, or N-type and P-type AlGaN, respectively.

On the other hand, the active region 59 includes a well layer 59a and a barrier layer 59b having a superlattice structure. The active region 59 may be a single quantum well structure having a single well layer 59a, and as illustrated, a multi quantum well in which a well lattice well layer 59a and a barrier layer 59b are alternately stacked. It may be a structure. That is, in the active region 59 of the multi-quantum well structure, the well layer 59a and the barrier layer 59b of the superlattice structure are alternately stacked on the N-type compound semiconductor layer 57. The barrier layer may be formed of GaN or AlGaN.

By forming the well layer 59a in a superlattice structure, crystal defects such as dislocations and pinholes can be prevented from occurring due to lattice mismatch between the well layer and the barrier layer.

3 is an enlarged cross-sectional view of the active region of FIG. 2 to illustrate a barrier layer of a superlattice structure according to embodiments of the present invention.

Referring to FIG. 3, the well layer 59a may have a superlattice structure formed by alternately growing InN and GaN. For example, an In source and an N source are introduced into a chamber using a MOCVD process to grow InN, and then the In source is stopped and the Ga source is introduced to grow GaN, and again the Ga source is stopped and the In source is stopped. The well layer 59a of the superlattice structure is grown by repeating the growth of InN by inflowing.

At this time, while the InN is grown, the Ga source remaining in the chamber may react with each other to form an In _x Ga _{1 - x} N layer 71a. In addition, the In source remaining in the chamber during the growth of GaN may be formed. May react together to form an In _y Ga _{1 - y} N layer 71b. Where 0 ≦ x, y ≦ 1, and x> y. The In _x Ga _{1 - x} N and In _y Ga _{1 - y} N may be repeatedly formed in a 800 ~ 900 ℃ thickness of using the MOCVD technique, for example, 2.5 to 20Å range from, In _x Ga _{1 - x} N By adjusting the composition of In in the light, light in the near ultraviolet or visible light region can be realized.

In this embodiment, by forming the well layer 59a in a superlattice structure, crystal defects caused by lattice mismatch between the well layer 59a and the barrier layer 59b can be prevented.

Meanwhile, in the present embodiment, the well layer 59a is first formed on the N-type semiconductor layer 57, but the barrier layer 59b is first formed on the N-type semiconductor layer 57 and then the well layer is formed. You may form 59a. In addition, although the In _x Ga _{1 - x} N layer 71a is first formed and the In _y Ga _1-y N layer 71b is illustrated and described, the order may be changed.

4 is a cross-sectional view for describing a light emitting diode according to another exemplary embodiment of the present invention.

Referring to FIG. 4, as described with reference to FIGS. 2 and 3, a buffer layer, an N-type compound semiconductor layer 57, and a P-type compound semiconductor layer 61 are positioned on the substrate 51, and the N-type compound is located. An active region 59 is interposed between the semiconductor layer 57 and the P-type compound semiconductor layer 61. In addition, the active region 59 includes a well layer 59a having a superlattice structure. However, in the present embodiment, the barrier layer 59b also has a superlattice structure.

As described with reference to FIG. 3, the barrier layer 59b of the superlattice structure may be a superlattice structure formed by alternately growing InN and GaN. For example, an In source and an N source are introduced into a chamber using a MOCVD process to grow InN, and then the In source is stopped and the Ga source is introduced to grow GaN, and again the Ga source is stopped and the In source is stopped. The barrier layer 59a of the superlattice structure is grown by repeating the growth of InN by flowing in.

At this time, while the InN is grown, the Ga source remaining in the chamber may react together to form an In _u Ga _{1- u} N layer 73a. In addition, the In source remaining in the chamber may be formed while growing the GaN. Reacts together to form an In _v Ga _{1 - v} N layer 73b. Here, 0 ≦ u, v ≦ 1, and u> v. The In _u Ga _{1 -u} N and In _v Ga _{1 - v} N may be repeatedly formed in a thickness of, for example, range from 2.5 to 20Å using the MOCVD technique at 800 ~ 900 ℃.

On the other hand, the barrier layer 59b has a wider bandgap than the well layer 59a. In general, the smaller the In composition ratio in the InGaN layer, the larger the bandgap. Thus, the In composition ratio v of the In _v Ga _{1 - v} N layer 73b is the In _x Ga _{1 - x} N layer (see FIG. 3). The In _v Ga _{1 - v} N layer 73b is grown to have a value relatively smaller than the In composition ratio x of 71a).

In the present embodiment, by forming the barrier layer 59a in a superlattice structure, crystal defects caused by lattice mismatch between the well layer 59a and the barrier layer 59b can be further prevented.

On the other hand, in the present embodiment, forming the In _u Ga _{1 -u} N layer (73a) first, and In _v Ga _{1 -} Although shown and described as forming the N _v layer (73b), the order may be reversed.

In addition, in embodiments of the present invention, the N-type compound semiconductor layer 57 and the P-type compound semiconductor layer 61 may be interchanged with each other.

According to embodiments of the present invention, by employing a superlattice well layer, it is possible to provide a light emitting diode capable of improving light efficiency by reducing occurrence of crystal defects such as dislocations or pinholes due to lattice mismatch in the active region. .

Claims (9)

A light emitting diode having an active region between a gallium nitride series N-type compound semiconductor layer and a gallium nitride series P-type compound semiconductor layer, The active region includes a well layer and a barrier layer of a superlattice structure. The method according to claim 1, The well layer of the superlattice structure is It is a superlattice structure formed by alternately growing InN and GaN, The barrier layer is formed of GaN. The method according to claim 1, The well layer has a superlattice structure in which In _x Ga _{1 - x} N and In _y Ga _{1 - y} N are alternately stacked, wherein 0 ≦ x, y ≦ 1, and x> y. The method according to claim 3, The barrier layer is a light emitting diode, characterized in that the superlattice structure. The method according to claim 4, wherein the barrier layer of the superlattice structure And a superlattice structure formed by alternately growing the InN and GaN. The method according to claim 4, The second barrier layer of a grid structure In _u Ga _{1 -u} N and In _v Ga _{1 -} a, and _v N a superlattice structure are alternately laminated by, 0≤u, v≤1 and, u> v, v <x A light emitting diode, characterized in that. The method according to claim 1, The barrier layer is a light emitting diode, characterized in that the superlattice structure. The method according to claim 7, wherein the barrier layer of the superlattice structure And a superlattice structure formed by alternately growing the InN and GaN. The method according to claim 7, And N _v is the shift of a superlattice structure as a stacked, 0≤u, v≤1 and, u> v, _- a barrier layer of the super lattice structure is In _u Ga _{1 -u} N and In _v Ga ₁ The In _v Ga _{1 - v} N has a larger band gap than the well layer of the superlattice structure.

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