KR20090003465A - Light emitting diode having active region of multi quantum well structure - Google Patents

Abstract

The light emitting diode having the active area of the multi quantum well structure is provided to control the recombination location of electrons and holes and to improve the luminous efficiency. The light emitting diode comprises the active area(59) of the multi quantum well structure in which the well layer and barrier are by turns laminated between the N type compound semiconductor layer(57) of the gallium nitride group and the P-type compound semiconductor layer(63) of the gallium nitride group. The light emitting diode is positioned between the first barrier(59a) adjacent to the N type compound semiconductor layer and the n barrier(59b) adjacent to the P-type compound semiconductor layer. The interlayer barrier is located in the central part between the n barrier and the first barrier. The first and n barrier are formed with the InxAlyGazN (<x<1, 0<=y<1, 0<z<1) or GaN. The interlayer barrier is formed with AlGaN.

Description

LIGHT EMITTING DIODE HAVING ACTIVE REGION OF MULTI QUANTUM WELL STRUCTURE}

1 is a cross-sectional view illustrating a light emitting diode having an active region of a conventional multi-quantum well structure.

2 is a band diagram for explaining the active region of the conventional multi-quantum well structure.

3 is a cross-sectional view for describing a light emitting diode having an active region of a multi-quantum well structure according to an exemplary embodiment of the present invention.

4 is a band diagram for explaining an active region of a multi-quantum well structure according to an embodiment of the present invention.

5 is a band diode gram for explaining an active region of a multi-quantum well structure according to another embodiment of the present invention.

6 is a band diagram for explaining an active region of a multi-quantum well structure according to another embodiment of the present invention.

7 is a band diagram illustrating an intermediate barrier layer in accordance with some embodiments of the present invention.

The present invention relates to a light emitting diode, and more particularly, to a light emitting diode having an active region of a multi-quantum well structure having improved light emission efficiency by adjusting a position where recombination of electrons and holes occurs.

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.

1 is a cross-sectional view illustrating a light emitting diode having an active region of a conventional multi-quantum well structure, and FIG. 2 is a band diagram illustrating an active region of a multi-quantum well structure of FIG. 1.

Referring to FIGS. 1 and 2, the light emitting diode includes an N-type semiconductor layer 17 and a P-type semiconductor layer 23, and an active region between the N-type and P-type semiconductor layers 17 and 23. 19) is interposed. In addition, a P-type cladding layer 21 having a relatively wide band gap may be interposed between the P-type semiconductor layer 23 and the active region 19 to increase the recombination efficiency of electrons and holes, and the N-type semiconductor layer An N-type cladding layer (not shown) may be interposed between the 17 and the active region 19.

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 generally formed of a multi-quantum well structure in which the well layer 19a and the barrier layer 19b are alternately stacked. In an InGaN light emitting diode, an active region of a multi-quantum well structure is generally 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 ℃.

The light emitting diode according to the prior art adopts a multi-quantum well structure to improve the luminous efficiency compared to a light emitting diode having a single quantum well structure, and in addition to the cladding layer 21 to increase the recombination efficiency. However, since the mobility of electrons is about 100 times higher than the mobility of holes, electrons move in a multi-quantum well structure relatively quickly than holes, and thus the position where electrons and holes are recombined is a P-type cladding layer. 21 is concentrated near. The P-type cladding layer is formed of AlGaN having a relatively wide band gap. Therefore, since the P-type cladding layer has a large crystal mismatch with respect to GaN or InGaN and contains impurities such as Mg, many crystal defects exist between the P-type cladding layer and the active region 19. These crystal defects cause non-luminescence recombination to reduce the luminous efficiency of the light emitting diode.

The well layer 19a may be in contact with the cladding layer 21 by arranging a well layer on top of a multi-quantum well structure in order to improve light emission efficiency due to recombination of electrons and holes as compared with non-emitting recombination. According to this, electrons concentrated near the cladding layer 21 are expected to combine with holes in the best well layer 19a to improve luminous efficiency. However, since the crystal mismatch between the best well layer 19a and the P-type cladding layer 21 increases more than the crystal mismatch between the barrier layer 19b and the P-type cladding layer 21, crystal defects near the cladding layer 21 are observed. This further increases the luminous efficiency is difficult to expect.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a light emitting diode having improved luminous efficiency by adjusting a position where electrons and holes recombine within a multi-quantum well structure.

Another object of the present invention is to provide a light emitting diode capable of increasing the recombination rate of electrons and holes in the central portion of the multi-quantum well structure.

In order to achieve the above technical problem, the present invention provides a light emission having an active region of a multi-quantum well structure in which a well layer and a barrier layer are alternately stacked between a gallium nitride-based N-type compound semiconductor layer and a gallium nitride-based P-type compound semiconductor layer. Provide a diode. The light emitting diode includes a first barrier layer adjacent to the N-type compound semiconductor layer and an intermediate barrier layer having a relatively wide band gap compared to the n-th barrier layer adjacent to the P-type compound semiconductor layer. The intermediate barrier layer is located between the first and nth barrier layers. The intermediate barrier layer may control a rate at which electrons move to control a position at which electrons and holes recombine within a multi-quantum well structure, and thus, a ratio generated near the P-type compound semiconductor layer or near the P-type cladding layer. By reducing the light emitting recombination it is possible to improve the light emitting efficiency of the light emitting diode.

One or more barrier layers may be present between the first and n-th barrier layers, and the intermediate barrier layer may be located anywhere between the first and n-th barrier layers. For example, the intermediate barrier layer may be located at the center between the first and nth barrier layers. In this case, the position where electrons and holes recombine are moved toward the center of the multi-quantum well structure, thereby improving luminous efficiency.

Another intermediate barrier layer having a relatively wider bandgap than the first barrier layer and the nth barrier layer may be located between the first barrier layer and the intermediate barrier layer. That is, a plurality of intermediate barrier layers may be located between the first and n-th barrier layers, and the intermediate barrier layers control the recombination positions of the electrons and the holes by limiting the movement of electrons.

Meanwhile, at least one barrier layer having a narrower bandgap than the middle barrier layer and other middle barrier layers may be located between the middle barrier layer and the other middle barrier layer. Accordingly, the recombination rate of electrons and holes increases between the intermediate barrier layer and the other intermediate barrier layer. In addition, the other intermediate barrier layer may have the same bandgap as the intermediate barrier layer, but is not limited thereto, and may have a narrower bandgap than the intermediate barrier layer.

In some example embodiments, the first and nth barrier layers may be formed of In _x Al _y Ga _z N (0 <x <1, 0 ≦ y <1, 0 <z <1) or GaN. The intermediate barrier layer or the other intermediate barrier layer may be formed of AlGaN.

Meanwhile, the intermediate barrier layer or the other intermediate barrier layer may be a laminated structure in which a layer having a relatively wide band gap is interposed between the layers having a relatively narrow band gap. Here, the overall bandgap of the laminated structure is defined by the relatively wide bandgap. This stacking structure mitigates lattice mismatch between layers with relatively wide bandgap and adjacent well layers to prevent occurrence of crystal defects.

In addition, each of the relatively narrow bandgap layers is a layer formed of In _x Al _y Ga _z N (0 <x <1, 0 ≦ y <1, 0 <z <1) or GaN, and the relatively The layer with a wide bandgap may be a layer formed of AlGaN.

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.

3 is a cross-sectional view illustrating a light emitting diode having an active region of a multi-quantum well structure according to an embodiment of the present invention, and FIG. 4 illustrates an active region of a multi-quantum well structure according to an embodiment of the present invention. Band diagram.

Referring to FIG. 3, 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, N GaN doped with undoped GaN or N-type impurities. Can be.

A P-type compound semiconductor layer 63 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 63. . 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 63 may be N-type and P-type GaN, or N-type and P-type AlGaN, respectively. In addition, a P-type cladding layer 61 may be interposed between the P-type compound semiconductor layer 63 and the active region 59. The P-type cladding layer 61 may also be formed of a Group III nitride semiconductor layer of (Al, In, Ga) N series, for example, AlGaN. Although not shown, an N-type cladding layer may be interposed between the N-type compound semiconductor layer 57 and the active region 59.

On the other hand, the active region 59 has a multi-quantum well structure including a well layer 59a and a barrier layer 59b stacked alternately. The well layer 59a may be formed of (Al, In, Ga) N, and its composition element and composition range may be selected according to the wavelength of light required. The well layer 59a may be, for example, InGaN. The barrier layer 59b may be formed of In _x Al _y Ga _z N (0 <x <1, 0 ≦ y <1, 0 <z <1) or GaN. Although the well layer 59a is shown in contact with the N-type compound semiconductor layer 57, the barrier layer 59b may be in contact, and the barrier layer 59b is in contact with the P-type cladding layer 61. The well layer 59a may be in contact.

In addition, the active region 59 includes an intermediate barrier layer 59c having a wider bandgap than the barrier layers 59b. The intermediate barrier layer 59c may be formed of, for example, (Al, In, Ga) N, for example, AlGaN. An active region 59 of the multi-quantum well structure including the intermediate barrier layer 59c will be described in detail with reference to FIG. 4.

Referring to FIG. 4, the active region 59 of the multi-quantum well structure is located between the N-type compound semiconductor layer 57 and the P-type compound semiconductor layer 63 or the P-type cladding layer 61. The active region 59 is formed by alternately stacking a well layer 59a having a relatively narrow band gap and a barrier layer 59b having a relatively wide band gap. For convenience, the barrier layer adjacent to the N-type compound semiconductor layer is defined as the first barrier layer 59b-1, and the barrier layer adjacent to the P-type compound semiconductor layer 63 or the P-type cladding layer 61 is removed. n barrier layer 59b-n.

Among the barrier layers, an intermediate barrier layer 59c having a wider bandgap than the first and n-th barrier layers is disposed between the first barrier layer 59b-1 and the n-th barrier layer 59b-n. Located in Since the intermediate barrier layer 59c has a relatively wide bandgap, when electrons introduced from the N-type compound semiconductor layer 57 pass through the active region 59, the movement of the electrons is restricted. Accordingly, the position where electrons and holes are recombined by the intermediate barrier layer 59c may be adjusted. For example, when the intermediate barrier layer 59c is disposed at the center of the first and nth barrier layers, a position where electrons and holes recombine may be moved toward the center of the multiquantum well.

By moving the position where electrons and holes recombine into the multi-quantum well structure, electrons can be prevented from being concentrated near the P-type cladding layer 61, thereby reducing non-emitting recombination and improving luminous efficiency. Can be.

Meanwhile, in addition to the intermediate barrier layer 59c, another intermediate barrier layer having a relatively wider band gap than the first and nth barrier layers may be located in the multi-quantum well structure. This will be described in detail with reference to FIGS. 5 and 6.

5 is a band diagram illustrating an active region of a multi-quantum well structure according to another embodiment of the present invention.

Referring to FIG. 5, as described with reference to FIG. 4, an intermediate barrier having a relatively wide band gap between the first barrier layer 59b-1 and the n-th barrier layer 59b-n compared to these barrier layers. Layer 59c is located. In addition, another intermediate barrier layer 59c 'with a relatively wide bandgap is positioned between the first barrier layer 59b-1 and the nth barrier layer 59b-n. The other intermediate barrier layer 59c 'may be located between the first barrier layer and the intermediate barrier layer 59c.

The other intermediate barrier layer 59c 'has a relatively wide bandgap like the intermediate barrier layer 59c to limit the movement of electrons. In particular, when the other intermediate barrier layer 59c 'is disposed close to the intermediate barrier layer 59c, the recombination rate of electrons and holes is further increased near the intermediate barrier layer 59c. In addition, as illustrated, at least one barrier layer having a relatively narrow bandgap may be interposed between the intermediate barrier layer 59c and the other intermediate barrier layer 59c '. Accordingly, the recombination rate of electrons and holes may be increased between the intermediate barrier layer 59c and the other intermediate barrier layer 59c '.

The other intermediate barrier layer 59c 'may be formed of the same composition and composition ratio as AlGaN, but the present invention is not limited thereto. The other intermediate barrier layer 59c' may be formed of, for example, Al, In or Ga. N may be formed. For example, as shown in FIG. 6, another intermediate barrier layer 59m having a narrower bandgap compared to the intermediate barrier layer 59c may be disposed between the first barrier layer and the intermediate barrier layer 59c. .

Meanwhile, as described above, the intermediate barrier layer 59c or the other intermediate barrier layer 59c 'or 59m may be formed as a single layer, but is not limited thereto. For example, as shown in FIG. 7, the intermediate barrier layer 59c and / or the other intermediate barrier layer 59c 'or 59m may have a relatively wide bandgap between the layers 58a and 58b having a relatively narrow bandgap. It may be a laminated structure having a layer 58c having a. For example, each of the relatively narrow bandgap layers 58a and 58b may be formed of In _x Al _y Ga _z N (0 <x <1, 0 ≦ y <1, 0 <z <1) or GaN. The layer 58c having the relatively wide band gap may be formed of AlGaN.

This stacking structure mitigates lattice mismatch between the intermediate barrier layer 59c or other intermediate barrier layer and the well layers 59a adjacent thereto to prevent the occurrence of crystal defects.

In embodiments of the present invention, the first barrier layer and the n-th barrier layer may have the same band gap, but are not limited thereto and may have different band gaps. In addition, the active region 59 of the multi-quantum well structure may further include barrier layers in addition to the first barrier layer and the nth barrier layer, and further include intermediate barrier layers in addition to the intermediate barrier layer or other intermediate barrier layers. You may.

According to embodiments of the present invention, an intermediate barrier layer having a relatively wide bandgap may be used to adjust a position where electrons and holes recombine within a multi-quantum well structure of a light emitting diode. In particular, the intermediate barrier layer may be disposed in the center of the multi-quantum well structure to provide a light emitting diode having an increased recombination rate between electrons and holes. Accordingly, non-light emitting recombination generated near the P-type compound semiconductor layer or the P-type cladding layer may be reduced to improve the luminous efficiency of the light emitting diode.

Claims (8)

A light emitting diode having an active region of a multi-quantum well structure in which a well layer and a barrier layer are alternately stacked between a gallium nitride series N-type compound semiconductor layer and a gallium nitride series P-type compound semiconductor layer, An intermediate barrier positioned between the first barrier layer adjacent to the N-type compound semiconductor layer and the n-th barrier layer adjacent to the P-type compound semiconductor layer and having a relatively wider bandgap than the first barrier layer and the n-th barrier layer A light emitting diode comprising a layer. The method according to claim 1, And the intermediate barrier layer is positioned centrally between the first barrier layer and the nth barrier layer. The method according to claim 1, And another intermediate barrier layer positioned between the first barrier layer and the intermediate barrier layer and having a relatively wider bandgap than the first barrier layer and the nth barrier layer. The method according to claim 3, At least one barrier layer having a narrower bandgap than said intermediate barrier layer and other intermediate barrier layers is located between said intermediate barrier layer and said other intermediate barrier layer. The method according to claim 3, And the other intermediate barrier layer has a relatively narrow bandgap compared to the intermediate barrier layer. The method according to any one of claims 1 to 5, The first and nth barrier layers are formed of In _x Al _y Ga _z N (0 <x <1, 0 ≦ y <1, 0 <z <1) or GaN, The intermediate barrier layer or the other intermediate barrier layer is formed of AlGaN. The method according to any one of claims 1 to 5, The intermediate barrier layer or the other intermediate barrier layer is a light emitting diode, characterized in that the laminated structure having a layer having a relatively wide band gap between the layers having a relatively narrow band gap. The method according to claim 7, Each of the relatively narrow bandgap layers is a layer formed of In _x Al _y Ga _z N (0 <x <1, 0 ≦ y <1, 0 <z <1) or GaN, The light emitting diode, characterized in that the layer having a relatively wide band gap is a layer formed of AlGaN.

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