KR101111749B1

KR101111749B1 - Nitride Semiconductor Light Emitting Device Using Multilayer Struture Quantum Barrier

Info

Publication number: KR101111749B1
Application number: KR1020080126087A
Authority: KR
Inventors: 정훈재; 손철수; 최락준; 이수민
Original assignee: 삼성엘이디 주식회사
Priority date: 2008-12-11
Filing date: 2008-12-11
Publication date: 2012-03-09
Also published as: KR20100067504A

Abstract

The present invention relates to a nitride semiconductor light emitting device having a high luminous efficiency. A nitride semiconductor light emitting device according to an aspect of the present invention, an n-type nitride semiconductor layer and a p-type nitride semiconductor layer; And an active layer interposed between the n-type nitride semiconductor layer and the p-type nitride semiconductor layer, the active layer having a multi-quantum well structure having a plurality of quantum well layers and at least one quantum barrier layer, wherein the quantum barrier layer is Al _x In. A first layer of _1-x N (0 ≦ _x ≦ 0.3) and a second layer of Al _y In _1-y N (0.7 ≦ _y ≦ ₁ ) are alternately stacked to form a multi-layered AlInN quantum barrier of at least three layers in total. It is in layers.

Nitride semiconductor, LED

Description

Nitride semiconductor light emitting device using multi-layered quantum barriers {Nitride Semiconductor Light Emitting Device Using Multilayer Struture Quantum Barrier}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor light emitting device, and more particularly, to alleviate polarization in a quantum well in an active layer having a multi-quantum well (MQW) structure and to increase the overlap region of the wave function of electrons and holes, thereby improving high luminous efficiency. A nitride semiconductor light emitting device that can be represented.

After the development of nitride semiconductor light emitting devices (eg, group III nitride compound semiconductor LEDs), nitride semiconductor light emitting devices have attracted attention as a next-generation main light source in various fields such as backlights for displays, flashes for cameras, and lighting. As the field of application of nitride semiconductor light emitting devices is expanded, efforts have been made to increase luminance and luminous efficiency.

A nitride semiconductor light emitting device such as a group III nitride semiconductor LED includes an n-type semiconductor layer and a p-type semiconductor layer and an active layer of a group III nitride compound interposed therebetween. The basic operating principle of the nitride semiconductor light emitting device is to inject electrons and holes into the active layer to combine the electrons and holes to emit light. In general, an active layer of a nitride semiconductor light emitting device includes a single quantum well (SQW) structure having a single quantum well layer and a multi-quantum well (MQW) structure having a plurality of quantum well layers. There is. The active layer of the double quantum well structure has better light efficiency than the single quantum well structure and has a high luminous output.

In the nitride semiconductor light emitting device, the active layer of the multi-quantum well structure described above may be formed of an InGaN quantum well and a GaN quantum barrier. A quantum well corresponds to a layer in which light is emitted by a combination of electrons and holes, and a quantum barrier is used to trap electrons and holes in a quantum well so that electrons and holes are better bonded. For high internal quantum efficiency, in order for electron and hole to be well coupled in InGaN quantum well, the area where the wave function of electron and the wave function of hole overlap each other should be wide. However, in the real light emitting device, due to the polarization phenomenon caused by the lattice mismatch caused by the lattice mismatch between the InGaN quantum well and the GaN quantum barrier, a strong electric field is generated in the active layer, which reduces the area where the wave functions of electrons and holes overlap each other in the quantum well. The electron-space space recombination efficiency is reduced and consequently the luminous efficiency is reduced.

In order to solve this problem, a growth of InAlGaN quantum barriers having a lattice constant similar to InGaN quantum wells and a bandgap similar to GaN quantum barriers has been proposed. However, the four-component InAlGaN quantum barrier has not been realized due to difficulties in growth conditions. AlInN may be considered as a quantum barrier material for the MQW active layer instead of the InAlGaN quantum barrier. InAlN has a large range of 0.7-6.2 eV in the band gap change due to the composition change of In. When AlInN, which has a composition with the same lattice constant as the InGaN quantum well generating blue wavelength, is used as the quantum barrier in the active layer, the band gap is 4.0 eV, which is larger than the GaN band gap of 3.4 eV, which effectively affects electrons and holes. It can be constrained to increase the luminous efficiency. However, due to the different conditions under which AlN and InN are effectively grown, it is difficult to grow an AlInN layer having a compositional ratio of Al and In so as to have a lattice constant equal to or similar to that of InGaN for the quantum barrier in the active layer. to be.

1 is a diagram schematically showing an energy band diagram of a conventional MQW structure active layer. As shown in FIG. 1, the In (indium) composition and the Al (aluminum) composition in the AlInN quantum barrier are constant throughout the AlInN quantum barrier. The In and Al compositions in the AlInN quantum barrier are determined in order to minimize lattice mismatch with the InGaN quantum well. In general, the growth optimum conditions of AlN and the growth optimum conditions of InN are different. Therefore, it is difficult to effectively infiltrate In and Al together and secure optimum crystallinity at the same time when AlInN has a significant Al and In content ratio.

One object of the present invention is to solve the above-mentioned problems, a high luminous efficiency nitride semiconductor that can improve the crystallinity by pursuing the effect of mitigating the polarization phenomenon through the elimination of lattice mismatch and at the same time solve the difficulty of quantum barrier layer growth It is to provide a light emitting device.

A nitride semiconductor light emitting device according to an aspect of the present invention, an n-type nitride semiconductor layer and a p-type nitride semiconductor layer; And an active layer interposed between the n-type nitride semiconductor layer and the p-type nitride semiconductor layer, the active layer having a multi-quantum well structure having a plurality of quantum well layers and at least one quantum barrier layer, wherein the quantum barrier layer is Al _x In. A first layer of _1-x N (0 ≦ _x ≦ 0.3) and a second layer of Al _y In _1-y N (0.7 ≦ _y ≦ ₁ ) are alternately stacked to form a multi-layered AlInN quantum barrier of at least three layers in total. It is characterized by being a layer.

According to an embodiment of the present invention, each of the first layer and the second layer may have a thickness of 0.5 nm or more and 5 nm or less.

The quantum barrier layer may be formed of an AlInN quantum barrier layer having a superlattice structure in which the first layer and the second layer are alternately stacked two or more times and have a plurality of first layers and a plurality of second layers.

According to an embodiment, in the AlInN quantum barrier layer of the superlattice structure, the plurality of first layers and the plurality of second layers may each have a constant band gap in the quantum barrier layer.

According to another embodiment, in the AlInN quantum barrier layer of the superlattice structure, the plurality of first layers or the plurality of second layers may have a different band gap in the quantum barrier layer.

The band gap of the second layer in the AlInN quantum barrier layer of the superlattice structure may be largest at an intermediate point within the thickness of the quantum barrier layer. Alternatively, the band gap of the second layer in the AlInN quantum barrier layer of the superlattice structure may be the smallest at the intermediate point within the thickness of the quantum barrier layer.

The quantum well layer may be formed of In _z Ga _1-z N (0 <z <1). The average composition of In in the quantum barrier layer may be less than or equal to the average composition of Al. In particular, the average composition ratio of Al and In in the quantum barrier layer may be 1: 1 to 4: 1.

The thickness of the quantum barrier layer may be 1 nm or more and 15 nm or less. The quantum well layer may have a thickness of 1 nm or more and 15 nm or less.

According to the present invention, in the nitride semiconductor light emitting device, the polarization phenomenon in the active layer is alleviated to increase the probability of electron-hole recombination, and the growth of the quantum barrier layer is easy, thereby making it possible to easily implement the improved crystalline active layer. Accordingly, not only the luminous efficiency of the nitride semiconductor light emitting device can be increased, but also a high crystalline high efficiency nitride semiconductor light emitting device can be easily realized.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. The shape and the size of the elements in the drawings may be exaggerated for clarity and the same elements are denoted by the same reference numerals in the drawings.

2 is a sectional view of a nitride semiconductor light emitting device according to an embodiment of the present invention. 3 is an energy band diagram schematically showing an example of the bandgap structure of the active layer 105 in the nitride semiconductor light emitting device of FIG. In FIG. 3, Ec and Ev represent edges of a conduction band and a valence band, respectively, in an energy band.

Referring to FIG. 2, the nitride semiconductor light emitting device 100 includes an n-type nitride semiconductor layer 103, an active layer 105, and a p-type nitride semiconductor layer 107 formed on a substrate 101 such as sapphire. The n-side electrode 110 may be formed on the n-type nitride semiconductor layer 103 exposed by mesa etching. In addition, the transparent electrode layer 108 and the p-layer electrode 109 may be formed on the p-type nitride semiconductor layer 107.

As shown in FIG. 2, the active layer 105 is an active layer having a multi-quantum well (MQW) structure having a plurality of quantum well layers 105a and at least one quantum barrier layer 105b. In this embodiment, for convenience, an active layer having two quantum well layers 105a and one quantum barrier layer 105b is illustrated, but the present invention is not limited thereto, and the active layer may have a larger number of quantum well layers and two or more layers. It may have a quantum barrier layer.

2 and 3, the quantum barrier layer 105b of the active layer 105 of the MQW structure has a multilayer structure. In particular, the first layer 115 is made of Al _x In _1-x N (0 ≦ _x ≦ 0.3) having a relatively high In component, and Al _y In _1-y N (0.7 ≦ _y ≦ ₁ having a relatively low In component). The second layer 125 of) is alternately stacked to form a multi-layer AlInN quantum barrier layer of three or more layers in total. As shown in FIG. 3, due to the difference in In composition described above, the second layer 125 has a larger energy bandgap than the first layer 115. The overall average composition of In and Al in the multi-layered AlInN quantum barrier layer 105b can approximate an Al _0.66 In _0.33 N composition having a lattice constant similar to that of InGaN quantum wells. The adjustment of the overall average composition of In and Al may be performed by adjusting the In content of the first layer 115 and the second layer 125 or by controlling the thickness of each layer 115 and 125. The quantum well layer 105a in the active layer 105 may be formed of In _z Ga _1-z N (0 <z <1).

As described above, the first layer 115 having an In content of 0.7 or more (ie, an Al content of 0.3 or less) and the second layer 125 having an In content of 0.3 or less (ie, an Al content of 0.7 or more) are alternately stacked. By forming the quantum barrier layer 105b in the active layer 105, the respective layers 115 and 125 of the first layer and the second layer can be easily grown to high crystallinity. In particular, the first layer 115 may be formed of InN, and the second layer 125 may be formed of AlN. Through the separate growth of InN and AlN it is possible to maximize the crystallinity of the quantum barrier layer in the active layer.

In addition, by using a multi-layered AlInN layer in which the first and second layers having different compositions are alternately stacked as quantum barriers in the active layer, polarization relaxation through eliminating lattice mismatch, which is an advantage of the conventional AlInN quantum barrier layer (see FIG. 1). The effect can be obtained.

Multi-layered structure in which the first layer 115 of Al _x In _1-x N (0 ≦ _x ≦ 0.3) and the second layer 125 of Al _y In _1-y N (0.7 ≦ _y ≦ ₁ ) are alternately stacked In order for the AlInN quantum barrier layer 105b to provide a sufficient barrier height in the active layer (that is, to sufficiently serve to trap electrons and holes in the quantum well layer 105a in the active layer), the quantum barrier layer ( The average composition of In in 105b) is more preferably equal to or smaller than the average composition of Al. In particular, the average composition ratio of Al and In in the quantum barrier layer 105b may range from 1: 1 to 4: 1.

AlN has the characteristics of an insulator that is not current-carrying in the case of general growth, whereas InN has an n-type characteristic that is well-current-carrying, so the first layer 115 of InN and the second layer 125 of AlN are ) Each is preferably thin. Even when the first layer 115 and the second layer 125 each have a composition of Al _x In _1-x N (0 < _x ≦ 0.3) and Al _y In _1-y N (0.7 ≦ _y <1), Each of the first and second layers 115 and 125 is preferably thin due to the difference in conductivity between the first and second layers 115 and 125. Preferably, each of the first layer 115 and the second layer 125 may have a thickness of 0.5 nm or more and 5 nm or less. In particular, more preferably, each of the first layer 115 and the second layer 125 may have a thickness of 0.5 nm or more and 2 nm or less. In addition, the thickness of the multi-layered AlInN quantum barrier layer 105b may have a range of 1 nm or more and 15 nm or less. In particular, the quantum barrier layer 105b of 5 nm or less is efficient in terms of electron movement. The thickness of the quantum well layer 105a may also have a range of 1 nm or more and 15 nm or less.

In the multi-layered AlInN quantum barrier layer 105b, the first layer 115 and the second layer 125 are alternately stacked two or more times to have a plurality of one layers 115 and a plurality of second layers 125. It may be made of an AlInN quantum barrier layer having a superlattice structure.

As shown in FIG. 3, in the AlInN quantum barrier layer 105b of the superlattice structure, the band gaps of the plurality of first layers 115 are constant in the quantum barrier layer 105b, and The band gap of the two layers 125 may also be constant within the quantum barrier layer 105b. In this case, the plurality of first layers 115 have a constant In composition (constant Al composition) over the thickness of the quantum barrier layer 105b, and the plurality of second layers 125 also have a thickness of the quantum barrier layer 105b. It has a constant In composition (constant Al composition) over. However, the present invention is not limited thereto, and by changing the In composition of the plurality of first layers 115 or the plurality of second layers 125, the plurality of first layers 115 or the plurality of second layers 125 may be used. You can also vary the bandgap of).

4 is an energy band diagram schematically showing a bandgap structure of an active layer according to another embodiment of the present invention. As shown in FIG. 4, in the AlInN quantum barrier layer 105b of the superlattice structure, the band gap of the second layer 125 is largest at an intermediate point within the thickness of the quantum barrier layer. Through such bandgap modulation, the bandgap of the quantum barrier can be obtained at the highest point in the thickness direction of the quantum barrier in the active layer. In this case, the effect of confining electrons and holes in the quantum well is increased, thereby reducing the leakage current, thereby enabling an increase in efficiency, particularly at a high current. This bandgap adjustment may be achieved through a gradual change in the In composition in the second layer 125.

5 is an energy band diagram schematically showing a bandgap structure of an active layer according to another embodiment of the present invention. As shown in FIG. 5, in the AlInN quantum barrier layer 105b of the superlattice structure, the band gap of the second layer 125 is the smallest at an intermediate point within the thickness of the quantum barrier layer. Through such bandgap modulation, the band gap of the quantum barrier can be obtained at the lowest point in the thickness direction of the quantum barrier in the active layer. In this case, there is an effect of increasing the rate at which electrons and holes cross the quantum barrier without large change in lattice constant.

Typically, the mobility of holes in the conventional nitride semiconductor light emitting device is lower than the mobility of electrons. By adjusting the bandgap of the AlInN quantum barrier layer 105b of the superlattice structure in the direction of improving the mobility of holes through a change in the In composition, the luminous efficiency may be particularly increased at low current.

In the above-described embodiments, the structure of the horizontal nitride semiconductor light emitting device in which both electrodes 109 and 110 are disposed on the same surface is illustrated (see FIG. 2), but the present invention is not limited thereto. It will be readily understood by those skilled in the art that the present invention can be applied to.

The present invention is not limited by the above-described embodiment and the accompanying drawings. It will be understood by those skilled 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, .

1 is an energy band diagram schematically showing a bandgap structure of an active layer in a conventional nitride semiconductor light emitting device.

2 is a cross-sectional view of a nitride semiconductor light emitting device according to an embodiment of the present invention.

3 is an energy band diagram schematically showing a bandgap structure of an active layer of a nitride semiconductor light emitting device according to an embodiment of the present invention.

4 is an energy band diagram schematically showing a bandgap structure of an active layer of a nitride semiconductor light emitting device according to another embodiment of the present invention.

5 is an energy band diagram schematically showing a bandgap structure of an active layer of a nitride semiconductor light emitting device according to another embodiment of the present invention.

100 nitride semiconductor light emitting device 101 substrate

103: n-type nitride semiconductor layer 105: active layer

105a: quantum well layer 105b: quantum barrier layer

107: p-type nitride semiconductor layer 108: transparent electrode layer

109: p-side electrode 110: n-side electrode

115: first layer 125: second layer

Claims

an n-type nitride semiconductor layer and a p-type nitride semiconductor layer; And

An active layer interposed between the n-type nitride semiconductor layer and the p-type nitride semiconductor layer, the active layer having a multi-quantum well structure having a plurality of quantum well layers and at least one quantum barrier layer,

The quantum barrier layer is formed by alternately stacking a _first layer of Al _x In _1-x N (0 ≦ _x ≦ 0.3) and a second layer of Al _y In _1-y N (0.7 ≦ _y ≦ ₁ ). A nitride semiconductor light emitting element comprising at least three layers of a multi-layered AlInN quantum barrier layer.

The method of claim 1,

The first and second layers each have a thickness of 0.5 nm or more and 5 nm or less.

The method of claim 1,

The quantum barrier layer comprises a nitride semiconductor AlInN quantum barrier layer having a plurality of first layers and a plurality of second layers of the first layer and the second layer alternately stacked two or more times Light emitting element.

The method of claim 3,

And in the AlInN quantum barrier layer of the superlattice structure, the plurality of first layers and the plurality of second layers each have a constant band gap in the quantum barrier layer.

The method of claim 3,

In the AlInN quantum barrier layer of the superlattice structure, the plurality of first layer or the plurality of second layer is characterized in that the band gap is different in the quantum barrier layer.

The method of claim 3,

And a band gap of the second layer is largest at an intermediate point within the thickness of the quantum barrier layer in the AlInN quantum barrier layer of the superlattice structure.

The method of claim 3,

And a band gap of the second layer is the smallest at an intermediate point within the thickness of the quantum barrier layer in the AlInN quantum barrier layer of the superlattice structure.

The method of claim 1,

The quantum well layer is nitride semiconductor light emitting device, characterized in that consisting of In _z Ga _1-z N (0 <z <1).

The method of claim 1,

The average composition of In in the quantum barrier layer is a nitride semiconductor light emitting device, characterized in that less than or equal to the average composition of Al.

10. The method of claim 9,

The nitride semiconductor light emitting device of claim 1, wherein the average composition ratio of Al and In in the quantum barrier layer is 1: 1 to 4: 1.

The method of claim 1,

The thickness of the quantum barrier layer is a nitride semiconductor light emitting device, characterized in that 1 nm or more and 15 nm or less.

The method of claim 1,

The thickness of the quantum well layer is a nitride semiconductor light emitting device, characterized in that more than 1nm 15nm.