KR101244583B1 - Light emitting diode having Active layer with Saw tooth shaped energy bandgap - Google Patents

Abstract

Disclosed is a light emitting device having an active layer having a sawtooth shaped energy bandgap. In the light emitting device according to the present invention, the active layer region may be set to have a sawtooth-shaped energy band gap by continuously changing the composition ratio between materials constituting the active layer including a plurality of layers to have a value that sequentially increases or decreases. . Through this, it is possible to obtain a light emitting device having high brightness by maximizing the confinement effect of the electrons and holes flowing into the active layer.

Description

Light emitting diode having active layer with saw tooth shaped energy bandgap}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device having an active layer having a sawtooth shaped energy bandgap, and more particularly, to changing the composition ratio of the constituents of the active layer including a plurality of layers so that the bandgap energy increases and decreases sequentially. The present invention relates to a light emitting device having an active layer having an energy band gap in the form.

The light emitting diode (LED) adopts a structure in which an active layer having a low energy band gap is interposed between semiconductor materials having a large energy band gap, and uses spontaneous emission light in the active layer. That is, the active layer plays a role of generating light through recombination of electrons and holes. Therefore, one of the most essential technologies for improving the luminous efficiency of the light emitting device is to improve the quality of the active layer that actually emits light.

Currently, the most widely used active layer structure is a multi-quantum well (MQW) structure formed by repeatedly stacking a quantum barrier layer and a quantum well layer several times. In the active layer of the multi-quantum well structure as described above, electrons in the conduction band and holes in the valence band are trapped in the quantum well layer. As a result, the state density of the carrier in the quantum well layer increases, so that the efficiency of light emission recombination of electrons and holes increases. In addition, since the refractive index of the quantum well layer is larger than the refractive index of the external semiconductor material surrounding the quantum well layer, photons generated in the quantum well layer are also spatially trapped near the quantum well layer. Through the above process, the electrons and holes flowing into the active layer are constrained to the quantum well layer region to generate light.

1 is a diagram showing an energy band structure of a conventional active layer.

Referring to FIG. 1, when the active layer interposed between the n-type cladding layer and the p-type cladding layer is a multiple quantum well structure composed of a quantum barrier layer and a quantum well layer, each of the quantum barrier layer and the quantum well layer The composition ratio of the constituents was adjusted to be as constant as possible.

In addition, Korean Patent Laid-Open Publication No. 2002-0096377 discloses that when growing an InGaN quantum well layer in a III-V nitride-based light emitting device, the thickness of the InGaN layer grown in each step is the same, and the InGaN quantum well layer and the first and The composition of the quantum well layer growth method of the LED is characterized in that the composition ratio of the second InGaN barrier layer is constant, and the In composition of the InGaN quantum well layer is higher than the In composition of the first and second InGaN barrier layers. Is disclosed.

However, the active layer having the above structure has a limitation in improving the luminous efficiency due to the limitation of the energy barrier of the quantum barrier layer and the quantum well layer.

Accordingly, an object of the present invention is to maximize the confinement effect of electrons flowing in the n-type cladding layer and holes flowing in the p-type cladding layer by having a sawtooth shape in which the energy band gap of the active layer region is sequentially increased and decreased. To provide a light emitting device having an active layer having a sawtooth-shaped energy bandgap.

The present invention for achieving the above object is a conductive substrate, an n-type cladding layer formed on the conductive substrate, an active layer having a plurality of layers formed on the n-type cladding layer and p-type formed on the active layer It comprises a cladding layer, characterized in that the composition ratio of the constituents of the active layer is changed so that each bandgap energy of the plurality of layers sequentially increases and decreases.

The light emitting device having an active layer having a sawtooth-type energy bandgap according to the present invention has a sawtooth-type structure in which the energy bandgap of the active layer region increases and decreases to maximize the restraint effect of electrons and holes flowing into the active layer. There is an effect of obtaining a high brightness light emitting element.

1 is a diagram showing an energy band structure of a conventional active layer.
2A is a view showing a light emitting device according to the present invention.
2B is a diagram showing an energy band structure of a compound semiconductor layer.
FIG. 3A is a comparative example and illustrates an energy band structure of a light emitting device having a constant composition ratio of materials constituting the active layer.
3B is a diagram showing an energy band structure of an active layer according to the present invention.
4 is a view showing the electro-optical characteristics of a light emitting device having an active layer having an energy band structure of the comparative example and a light emitting device having an active layer having an energy band structure of the present invention.

The present invention is capable of various modifications and various forms, and specific embodiments are illustrated in the drawings and described in detail in the text. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. Like reference numerals are used for like elements in describing each drawing.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention.

2A is a view showing a light emitting device according to the present invention.

2B is a diagram showing an energy band structure of a compound semiconductor layer.

Referring to FIG. 2A, in the light emitting device according to the present invention, an n-type cladding layer 12 is grown on a substrate 10, and an active layer 14 is grown thereon. Subsequently, the p-type cladding layer 16 is grown on the active layer 14. As described above, these compound semiconductor layers constituting the present invention can be grown using various methods, such as metal organic chemical vapor deposition (MOCVD) or molecular beam growth (MBE) techniques. Each layer may again include sublayers as needed.

In addition, the p-type electrode 18 is formed on the p-type cladding layer 16 of the compound semiconductor layer sequentially stacked as described above, and the n-type electrode 20 is formed on the rear surface of the substrate 10 to form a vertical type. A light emitting device having a structure can be produced.

In this case, the conductive substrate may be a GaAs substrate, and the compound semiconductor layer may be an AlGaInP-based compound semiconductor layer. The GaAs substrate is suitable for growing AlGaInP epilayers, and serves to support growth of AlGaInP active layer having excellent internal quantum efficiency. In addition, the n-type cladding layer and the p-type cladding layer formed with the AlGaInP active layer interposed therebetween are formed of a material having a larger bandgap than the interposed AlGaInP active layer, thereby helping to recombine electrons and holes.

The active layer may have a plurality of _{layers, (Al x Ga 1 -x)} y In 1 - consists of a _y P (0≤x≤1, 0≤y≤1). In this case, the active layer having a sawtooth-shaped energy band structure may be formed by sequentially changing at least one of x and y.

Referring to FIG. 2B, the active layer including the plurality of layers may include at least one pair of tooth top layers and tooth bottom layers. In this case, the tooth upper layer and the tooth lower layer are defined as the tooth upper layer, and the layer having the smallest band gap is defined as the tooth lower layer based on the energy band gap of the active layer region. do.

At this time, the tooth top layer is _{(Al x1 Ga 1 -x1) y1} In 1 - has a composition of _{y1 P (0≤x 1 ≤1, 0≤y} 1 ≤1), the tooth bottom layer is (Al _x2 Ga _{1 - x2} ) _y2 In _{1 - y2} P (0 ≦ x ₂ ≦ 1, 0 ≦ y ₂ ≦ 1).

A plurality of layers having a composition ratio varying in order to sequentially increase or decrease between the at least one pair of tooth upper layers and the tooth lower layer defined as described above may be interposed. In this case, the plurality of intervening layers may have a value between the composition ratio of the upper tooth layer and the composition ratio of the lower tooth layer.

For example, when the value of x ₁ is set to 0.9 and the value of x ₂ is set to 0.1, the x value of each layer interposed between the tooth upper layer and the tooth lower layer, that is, the composition ratio of Al and Ga is from 0.9 to 0.1. It is set within the range of.

In more detail, the composition ratio of x which each layer has is set to decrease sequentially from 0.9 to 0.1, and when it reaches 0.1, it is set to increase sequentially from 0.1 to 0.9 again. That is, the x composition ratio of the plurality of layers interposed therebetween with respect to the tooth upper layer and the tooth lower layer repeats the cycle of sequentially increasing and decreasing the values of 0.9 and 0.1 as the highest value and the lowest value. At this time, the number of layers interposed between the top tooth and the bottom tooth layer is not limited, but in order to have a more precise saw tooth-shaped energy band structure formed in a plurality of layers by reducing the difference in the composition ratio of each layer It is desirable to.

As described above, each layer constituting the active layer region may be formed by changing only the composition ratio of x ₁ and x ₂ , that is, Al and Ga, and at this time, the composition ratio of y ₁ and y ₂ may be kept constant. . As a result, the lattice constant is kept constant, thereby producing a light emitting device having fewer physical defects.

On the other _{hand, (Al x1 Ga 1 -x1)} y1 In 1 - y1 P tooth top layer having a composition ratio of (0≤x1≤1, 0≤y1≤1) and _{(Al x2 Ga 1 -x2) y2} In 1 - y2 P In the tooth lower layer having a composition ratio of (0 ≦ x2 ≦ 1, 0 ≦ y2 ≦ 1), both the composition ratio of x and the composition ratio of y can be changed.

That is, the value of x ₁ may be set to 0.9, the value of x ₂ may be set to 0.1, the value of y ₁ may be set to 0.1, and the value of y ₂ may be set to 0.9. In this case, the x value and y value of each layer interposed between the tooth upper layer and the tooth lower layer have a range from 0.9 to 0.1, respectively.

The composition ratio of x and y of each layer is set to decrease sequentially from 0.9 to 0.1, and when it reaches 0.1, it is set to sequentially increase from 0.1 to 0.9 again. That is, the composition ratio of x and y of the plurality of layers interposed therebetween with respect to the tooth upper layer and the tooth lower layer may be set to repeat the cycle of increasing and decreasing sequentially with 0.9 and 0.1 as the highest value and the lowest value. At this time, the increase and decrease rate of the value of x and the increase and decrease rate of the y value may be the same, but are not limited thereto, and may have different increase and decrease rates.

As described above, the light emitting device having the active layer having a sawtooth-shaped energy band structure can be manufactured by continuously changing the composition ratio of the constituents of each layer constituting the active layer.

In addition, the n-type electrode 20 and the p-type electrode 18 may be formed of a metal thin layer such as Au, Ag or Al, which may be formed through electron beam (E-beam) deposition or thermal deposition.

As described above, the AlGaInP-based light emitting device using the GaAs substrate has an advantage of reproducing a variety of light from the red to the lime green region.

FIG. 3A is a comparative example and illustrates an energy band structure of a light emitting device having a constant composition ratio of materials constituting the active layer.

Referring to FIG. 3A, an AlGaInP-based light emitting device including a compound semiconductor layer in which an n-type cladding layer, an active layer, and a p-type cladding layer is sequentially grown is provided.

The n-type clad layer n-Al _x In _{1 - x} P is formed in a layer (0≤x≤1), and the composition ratio of the material constituting the layer is a _{n-Al 0 .5 In 0 .5} P, the p-type cladding layer is p-Al _x in _{1 - x} p is formed in a layer (0≤x≤1), the composition ratio of the material constituting the layer is a _{p-Al 0 .5 in 0 .5} p. In this case, the n-type cladding layer and the p-type cladding layer serve to confine the light emitted from the active layer.

In addition, the active layer is a quantum barrier layer of (Al _x Ga _{1 -x} ) _y In _{1 - y} P (0≤x≤1, 0≤y≤1) and (Al _x Ga _{1 -x} ) _y In _1-y P ( 0≤x≤1, formed of a quantum well layer of the multiple quantum well structure alternately stacked with a 0≤y≤1), the composition ratio of the materials constituting the quantum barrier layer is (Al _{0 .9} Ga _{0 .1} ) _0.5 in and _{0 .5} P, the composition ratio of the materials constituting the quantum well layer is _{(Al 0 .1 Ga 0 .9)} 0.5 in 0 .5 P.

In the active layer of the multi-quantum well structure as described above, light is generated by confining electrons and holes introduced into the active layer to the quantum well layer region. That is, light is generated using a confinement effect in which electrons in the conduction band and holes in the valence band are trapped in the quantum well layer. Therefore, as the difference in the bandgap energy between the quantum barrier layer and the quantum well layer, that is, the size of the energy barrier, the restraining effect may be maximized to increase the luminous efficiency.

However, since the quantum barrier layer and the quantum well layer are formed to have a constant thickness and composition ratio, the light emitting device having the compound semiconductor layer has a limit in maximizing the restraining effect by increasing the size of the energy barrier.

3B is a diagram showing an energy band structure of an active layer according to the present invention.

Referring to FIG. 3B, the light emitting device according to the present invention includes a compound semiconductor layer in which an n-type cladding layer, an active layer, and a p-type cladding layer are sequentially grown, and the n-type cladding layer is n-Al _x In _{1 - x.} is formed in a P layer (0≤x≤1), the composition ratio of the material constituting the layer is a _{n-Al 0 .5 in 0 .5} P , and wherein the p-type cladding layer is p-Al _x in _{1 - x} is formed in a P layer (0≤x≤1), the composition ratio of the material constituting the layer is a _{p-Al 0 .5 in 0 .5} P. At this time, the n-type cladding layer and the p-type cladding layer serves to constrain the light emitted from the active layer.

In addition, each of the plurality of layers constituting the active layer is formed of (Al _x Ga _{1 -x} ) _y In _{1 - y} P (0 ≦ x ≦ 1, 0 ≦ _y ≦ 1), and includes at least one pair of tooth upper layers and a tooth An underlayer may be provided. At this time, the tooth top layer is _{(Al 0 .9 Ga 0 .1)} 0.5 In 0 .5 P having a composition ratio of the tooth bottom layer is _{(Al 0 .1 Ga 0 .9)} 0.5 In 0 .5 P ratio of Has

A plurality of layers having a continuous composition ratio is interposed between the at least one pair of tooth upper layers and the tooth lower layers defined as above. At this time, the plurality of intervening layers are formed to have a value that sequentially increases or decreases within a range of 0.9 to 0.1, which is a value between the composition ratio of the tooth upper layer and the composition ratio of the tooth lower layer. Therefore, the composition ratio of Al and Ga among the constituent materials constituting each layer of the active layer region has a continuously changing value, and the light emitting device having the active layer region as described above has a sawtooth band gap.

4 is a view showing the electro-optical characteristics of a light emitting device having an active layer having an energy band structure of the comparative example and a light emitting device having an active layer having an energy band structure of the present invention.

Referring to FIG. 4, the driving voltage Vf of the light emitting device including the active layer having the energy band structure of the comparative example is 1.94V, and the luminance Iv is 69mcd. On the other hand, the driving voltage of the light emitting device having an active layer having a sawtooth-type energy band structure of the present invention is 1.93V, the brightness is 76mcd, the driving voltage is maintained at the same level, the brightness is about 10% improved Can be. In other words, it can be seen that a light emitting device having a high level of driving voltage can be obtained.

According to the present invention, a light emitting device including an active layer having a sawtooth shaped energy bandgap may be formed by continuously changing a composition ratio of each component such that the bandgap energy is sequentially increased or decreased in the material of the active layer including a plurality of layers. The luminous efficiency of the device is improved.

10: substrate 12: n-type cladding layer
14: active layer 16: p-type cladding layer
18: p-type electrode 20: n-type electrode

Claims (7)

Conductive substrates;
An n-type cladding layer formed on the conductive substrate;
An active layer having a plurality of layers formed on the n-type cladding layer; And
Including a p-type cladding layer formed on the active layer,
The active layer has at least one pair of structures having a plurality of layers having an energy bandgap that increases or decreases sequentially between the tooth upper layer having the largest energy bandgap and the tooth lower layer having the smallest energy bandgap,
The active layer has a composition ratio of (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x ≦ 1, 0 ≦ _y ≦ 1), and is based on x or y of the tooth upper layer and the tooth lower layer, The sawtooth energy bandgap is changed by changing x or y of the plurality of layers interposed between the tooth upper layer and the tooth lower layer to continuously increase or decrease in a range smaller than x or y of the tooth upper layer and the tooth lower layer. Forming light emitting element. delete delete The method of claim 1,
The tooth upper layer has a composition ratio of (Al _x1 Ga _1-x1 ) _y1 In _1-y1 P (0≤x ₁ ≤1, 0≤y ₁ ≤1), and the lower tooth layer is (Al _x2 Ga _1-x2 ) _y2 In _1-y2 P (0 ≦ x ₂ ≦ 1, 0 ≦ y ₂ ≦ 1), the composition ratio of y ₁ and y ₂ is kept constant, and the at least one pair of tooth upper and tooth lower layers each layer is a light emitting element, characterized in that has a value that sequentially increases or decreases in the range of composition of the x ₁ and x ₂ is located between the. The method of claim 1,
The tooth upper layer has a composition ratio of (Al _x1 Ga _1-x1 ) _y1 In _1-y1 P (0≤x ₁ ≤1, 0≤y ₁ ≤1), and the lower tooth layer is (Al _x2 Ga _1-x2 ) _y2 In _1-y2 P (0 ≦ x ₂ ≦ 1, 0 ≦ y ₂ ≦ 1), wherein each layer interposed between the at least one pair of tooth upper layers and the tooth lower layers is the x ₁ and the x ₂ A light emitting device having a value which sequentially increases and decreases within a range of the composition of and within the ranges of the composition of y ₁ and y ₂ . The method of claim 1,
The conductive substrate is a light emitting device, characterized in that the GaAs substrate. The method of claim 1,
The n-type and p-type cladding layers are formed of an AlGaInP-based compound semiconductor, and are formed of a material having a larger band gap than the active layer.

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