WO2010062119A2

WO2010062119A2 - Semiconductor light emitting element

Info

Publication number: WO2010062119A2
Application number: PCT/KR2009/007001
Authority: WO
Inventors: 안도열; 박승환; 김종욱; 구분회
Original assignee: 우리엘에스티 주식회사
Priority date: 2008-11-27
Filing date: 2009-11-26
Publication date: 2010-06-03
Also published as: KR20100060524A; WO2010062119A3; KR101012636B1

Abstract

The present disclosure relates to a semiconductor light emitting element that includes an active layer generating light through the recombination of electrons and holes. The active layer comprises: a quantum well made of a first compound semiconductor, and a barrier layer made of a second compound semiconductor. The quantum well includes: a first sub-quantum well having a first band gap; and a second sub-quantum well having a second band gap different from the first band gap.

Description

Semiconductor light emitting device

The present disclosure relates to a semiconductor light emitting device as a whole, and more particularly, to a semiconductor light emitting device capable of improving degradation of light emission characteristics due to piezoelectric fields and spontaneous polarization.

Here, the semiconductor light emitting device refers to a semiconductor optical device that generates light through recombination of electrons and holes, for example, a group III nitride semiconductor light emitting device. The group III nitride semiconductor consists of a compound of Al (x) Ga (y) In (1-x-y) N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). In addition, GaAs type semiconductor light emitting elements used for red light emission, etc. are mentioned.

This section provides background information related to the present disclosure which is not necessarily prior art.

The luminescence properties of semiconductor light emitting devices are degraded due to piezoelectric field and spontaneous polarization due to stress applied to the active layer, and this problem is more prominent in the group III nitride semiconductors constituting the blue and green light emitting devices. [Park et al. , Appl. Phys. Lett. 75, 1354 (1999).

In order to minimize piezo electric field and spontaneous polarization in group III nitride semiconductor, the following method has been proposed.

1) Method to minimize spontaneous polarization and piezo effect using non-polar or semi-polar substrate [Park et al., Phys Rev B 59, 4725 (1999) and Waltereit et al., Nature 406, 865 (2000) ].

2) The cladding layer is a four-layered film, and the composition ratio of Al is increased to increase the binding effect of the transmitter to increase the luminous efficiency [Zhang et al., Appl. Phys. Lett. 77, 2668 (2000), Lai et al., IEEE Photonics Technol Lett. 13, 559 (2001).

However, in the case of 1), the growth technology for the direction of heterocrystal growth is not yet mature, so there are many defects in device fabrication, so it is known that device characteristics are not as expected as the theoretical expectation, and the manufacturing process is very difficult [K] . Nishizuka et al., Appl. Phys. Lett. 87, 231901 (2005)].

In case of 2), it is not a fundamental solution because spontaneous polarization and piezo electric field cannot be eliminated fundamentally.

However, there is a theoretical study that the composition ratio of quaternary membranes in which the internal electric field due to piezoelectric and spontaneous polarization is extinguished can be found if the indium composition ratio in the quantum wells is determined in the InGaN / InGaAlN quantum well structure having the quaternary cladding layer. S. H Park, D. Ahn, J. W. Kim, Applied Physics Letters 92, 171115 (2008).

However, this method has the disadvantage that the growth conditions of the four-layer cladding layer are extremely demanding.

This will be described later in the section on Embodiments of the Invention.

This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all, provided that this is a summary of the disclosure. of its features).

According to one aspect of the present disclosure, in a semiconductor light emitting device having an active layer that generates light by recombination of electrons and holes, the active layer is provided as a first compound semiconductor. Quantum well layer; And a barrier layer formed of the second compound semiconductor, wherein the quantum well layer includes: a first sub quantum well layer having a first band gap; And a second sub quantum well layer having a second band gap having a different size from the first band gap.

This will be described later in the section on Embodiments of the Invention.

1 is a view showing an example of a semiconductor light emitting device according to the present disclosure;

2 is a view showing a band gap of the active layer according to the prior art the band gap of the active layer according to the present disclosure,

3 is a view comparing the light gain of the quantum well layer according to the present disclosure and the quantum well layer according to the prior art,

4 is a view showing a relationship between a thickness Lw1 and an indium (In) composition ratio x of a first sub quantum well layer according to the present disclosure;

5 is a view showing a relationship between a thickness Lw1 and a spontaneous emission rate of a first sub quantum well layer according to the present disclosure.

The present disclosure will now be described in detail with reference to the accompanying drawing (s).

1 is a view showing an example of a semiconductor light emitting device according to the present disclosure, the semiconductor light emitting device 100 includes an active layer 103 for generating light by recombination of electrons and holes, the active layer 103 A quantum well layer 113 and a barrier layer 123 are included, and the quantum well layer 113 includes first and second sub quantum well layers 113a and 113b.

Here, the active layer 103 may have a structure in which the quantum well layer 113 and the barrier layer 123 are alternately stacked several times, and the n-type contact layer injecting electrons (donors) into the active layer 103 ( 102, the p-type contact layer 104 and the n-type contact layer 102 which are disposed to face the n-type contact layer 102 with the active layer 103 therebetween and inject holes (acceptors) into the active layer 103. ), A substrate 101 for sequential stacking of the active layer 103 and the p-type contact layer 104 may be provided.

The n-side electrode 105 electrically connected to the n-type contact layer 102 and the p-side electrode 106 electrically connected to the p-type contact layer 104 in order to apply a voltage to the semiconductor light emitting device 100. ) May be provided.

When voltage is applied through the n-side electrode 105 and the p-side electrode 106, electrons are injected from the n-type contact layer 102 to the active layer 103, and the active layer 103 from the p-type contact layer 104. Holes are injected into the light, and light is generated by recombination of electrons and holes.

On the other hand, when the active layer 103, the n-type contact layer 102 and the p-type contact layer 104 is provided with a group III nitride semiconductor, the substrate 101 is a homogeneous substrate, GaN-based substrate is used as a heterogeneous substrate A sapphire substrate, a SiC substrate, a Si substrate, or the like may be used, and when the SiC substrate is used, the n-side electrode 105 may be formed on the SiC substrate side.

In addition, a buffer layer (not shown) may be further provided between the substrate 101 and the n-type contact layer 102. The buffer layer functions to reduce crystal defects generated when the group III nitride semiconductor layer is grown on a dissimilar substrate.

The buffer layer may be formed of a Group III nitride semiconductor that does not contain a dopant.

In addition, the n-type contact layer 102 and the p-type contact layer 104 may be formed of one or more Group III nitride semiconductor layers.

Meanwhile, in the present example, the quantum well layer 113 is provided with the first compound semiconductor, the barrier layer 123 is provided with the second compound semiconductor, and the first and second sub quantum well layers 113a and 113b are mutually supported. Each of the first and second band gaps has different sizes.

The first and second sub quantum well layers 113a and 113b may be provided by varying the composition ratio of each element forming the first compound semiconductor.

According to this, the quantum well layer 113 has a stepped band gap in the Ek space, and the light transition characteristic can be improved by being constrained to a position closer to the space between electrons and holes by the stepped band gap. have.

In addition, since the lattice constants of the barrier layer 123 and the quantum well layer 113 are different, strain is generated. Since the quantum well layer 113 is provided with two sub quantum well layers 113a and 113b, the strain is dispersed. The piezoelectric field may be reduced due to the dispersion of the strain, and thus the light transition characteristic may be improved.

In particular, when the active layer 103, the n-type contact layer 102 and the p-type contact layer 104 is provided with a Group III nitride semiconductor, the first compound semiconductor is provided with gallium nitride (InGaN), the second compound The semiconductor is preferably provided with gallium nitride (GaN).

In this case, the first sub quantum well layer 113a is formed of In (x) Ga (1-x) N, and the second sub quantum well layer 113b is formed of In (y) Ga (1-y) N. It is preferred that x and y have different values.

In particular, x has a value of 0.15 ≦ x ≦ 0.25, and y preferably has a value of 0 <y ≦ 0.075.

This is because when the value of y is larger than 0.075, the band gap difference with the barrier layer made of gallium nitride (GaN) becomes too large, so that the strain reduction effect is reduced.

Also, when the value of x is outside the above range, a wavelength other than the wavelength corresponding to blue light is emitted.

On the other hand, when the band gap of the first sub quantum well layer 113a is smaller than the band gap of the second sub quantum well layer 113b, electrons and holes are mostly constrained to the first sub quantum well layer 113a. Most of the photons that contribute to the emission wavelength may be generated in the one sub quantum well layer 113a.

In this case, a problem may arise in that the emission wavelength is increased due to the influence of the wave function of electrons and holes confined to the second sub quantum well layer 113b having a relatively large band gap.

One way to prevent this is to reduce the thickness of the second sub quantum well layer 113b to a thickness in which the second sub quantum well layer 113b can only disperse the strain.

However, for this purpose, since the second sub quantum well layer 113b having a very thin thickness is required, manufacturing is not easy.

Alternatively, both of electrons and holes constrained by the first sub quantum well layer 113a and the second sub quantum well layer 113b may be involved in light emission, thereby preventing the emission wavelength from being increased.

To this end, it is necessary to determine appropriate thicknesses of the first sub quantum well layer 113a and the second sub quantum well layer 113b.

Specifically, when the band gap of the first sub quantum well layer 113a is smaller than the band gap of the second sub quantum well layer 113b, the thickness of the first sub quantum well layer 113a is the second sub quantum well. It is preferably provided smaller than the thickness of the layer 113b.

A preferable ratio of the thickness of the first sub quantum well layer 113a and the thickness of the second sub quantum well layer 113b will be described later.

2 is a diagram illustrating a bandgap of an active layer according to the present disclosure and a bandgap of an active layer according to the prior art, (a), wherein the barrier layer is formed of GaN, the quantum well layer is formed of InGaN, and in the quantum well layer The composition of In is constant at 0.085, (b) the barrier layer is made of GaN, the quantum well layer is made of InGaN, and the quantum well layer is made of two layers having an In composition of 0.116 and 0.05. to be.

Comparing (a) and (b), (a) has a quantum well layer as one layer, so that a step is not formed in the band gap Lw of the quantum well layer, whereas (b) is a quantum well layer Since the two layers are provided, a step is formed in the band gaps Lw1 and Lw2 of the quantum well layer.

As a result, since the electrons and holes can be constrained in closer positions than in the case of (a), the light transition characteristics can be improved.

In addition, since the lattice constant of the barrier layer made of GaN and the quantum well layer made of InGaN are greatly different from each other, strain is generated. The piezoelectric field is formed by adjusting the indium (In) content of InGaN to include two quantum well layers. It is possible to disperse the strain that generates.

Therefore, the piezo electric field can be reduced, and as a result, the light transition characteristic can be improved.

3 is a view comparing light gain between a quantum well layer according to the present disclosure and a quantum well layer according to the prior art, in which (a) is a thickness of 3 nm and (b) is a quantum well layer The thickness of 5 nm.

In (a), in the case of the graph located on the left side (wavelength is 440 nm), the light gain corresponding to the quantum well layer according to the prior art (dotted line) and the light gain corresponding to the quantum well layer according to the present disclosure (solid line) Although there is no significant difference, in the case of the graph located on the right side (wavelength is 530 nm), the light gain (solid line) corresponding to the quantum well layer according to the present disclosure corresponds to the light gain (dotted line) corresponding to the quantum well layer according to the prior art. It can be seen that significantly improved compared to).

Further, in (b), the light gain (solid line) corresponding to the quantum well layer according to the present disclosure is shown in both the graph located on the left side (wavelength is 440 nm) and the graph located on the right side (wavelength is 530 nm). It can be seen that the optical gain (dotted line) corresponding to the quantum well layer according to the prior art is greatly improved.

Therefore, it can be seen that the effect of the quantum well layer according to the present disclosure increases with longer wavelength.

On the other hand, it can be seen that the size of the light gain is small in the case where the thickness of the quantum well layer is thick (b) as compared with the relatively thin thickness of the quantum well layer (a).

This is because as the quantum well layer increases in thickness, electrons and holes are distributed in a wider area, and thus the bonding probability decreases.

However, in (a) and (b), the degree of improvement of light gain by the quantum well layer according to the present disclosure, that is, the light gain (dotted line) corresponding to the quantum well layer according to the prior art and the quantum well according to the present disclosure It can be seen that the difference in light gain (solid line) corresponding to the layer is larger when the thickness of the quantum well layer is thicker (b) than when the thickness of the quantum well layer is relatively thin (a).

The result shown in FIG. 3 is a result of numerical calculation using the following equation.

First, the optical gain spectrum was calculated using a non-Macobian gain model with a multibody effect. (S. H. Park, S. L. Chung, and D Ahn, "Interband relaxation time effects on non-Markovian gain with many-body effects and comparison with experiment", Semicond. Sci. Technol., Vol. 15 pp. 2003-2008).

The optical gain with the multibody effect including the effect of the anisotropy of valence versus dispersion is expressed by the following equation.

Equation 1

Where ω is the angular velocity, M ₀ is the permeability in vacuum, ε is the dielectric constant, σ = U (or L) is the upper (or lower) block of the effective mass Hamiltonian, and e is the electron Charge, m ₀ is the mass of free electrons, k _|| Is the magnitude of the surface wave vector in the quantum well plane, Lw is the width of the well, and | M _nm | ² is the matrix component of the strained quantum well. In addition, f _n ^c and f _m ^v are Fermi functions for the probability of electron occupancy in the conduction band and valence band, respectively, and the subscripts n and m represent the electron and hole states in the conduction band, respectively.

In addition, the re-standardized transition energy of electrons and constant space is represented by Equation 2 below.

Equation 2

Where E _g is the bandgap, ΔE _8X and ΔE _CH are the screened exchange and Coulomb-hole contributions to the bandgap renormalization, respectively (see WW Chow, M. Hagerott, A. Bimdt, and SW Koch, "Threshold coditions for an ultraviolet wavelength GaN quantum-well laser", IEEE J. Select. Topics Quantum Electron., Vol. 4, pp. 514-519, 1998).

A Gaussian line shape function L (ω, k _|| , φ) is expressed by Equation 3 below.

Equation 3

In the above equation, it is the cause of the coulomb rise of the exitonic or interband transition. The line shape function is the simplest Gaussian of Non-Marcobian Quantum kinetics and is described by Equations 4 and 5 below.

Equation 4

Equation 5

The interband relaxation time? In and the correlation time? C are regarded as constants and are calculated to be 25fs and 10fs, respectively. The parameters of GaN and InN materials required for the calculation are given by Table 1 below.

Table 1

4 is a view showing the relationship between the thickness (Lw1) and the indium (In) composition ratio (x) of the first sub quantum well layer according to the present disclosure, the emission wavelength is 440nm, the thickness of the quantum well layer is 50Å. And In (x) Ga (1-x) N, the thickness Lw1 of the first sub quantum well layer is changed, and the indium composition ratio x of the first sub quantum well layer is calculated.

Here, the band gap of the first sub quantum well layer is relatively smaller than the band gap of the second sub quantum well layer, and is indium of the second sub quantum well layer provided with In (y) Ga (1-y) N. (In) The composition ratio y was set to 0.05.

Referring to FIG. 4, it can be seen that the indium (In) composition ratio x of the first sub quantum well layer decreases as the thickness Lw1 of the first sub quantum well layer having a relatively small band gap is increased.

This is because when the thickness w1 of the first sub quantum well layer having the relatively small band gap increases, the influence of the relatively small band gap increases, so that the wavelength of the light emitted tends to increase. Since the band gap of the first sub quantum well layer is increased to compensate for this, the band gap increases as the indium (In) content decreases, so that the first gap is generated to generate light having a fixed emission wavelength. This is because the indium (In) content of the sub quantum well layer should be reduced.

FIG. 5 is a view illustrating a relationship between a thickness Lw1 of a first sub quantum well layer and a spontaneous emission rate according to the present disclosure. The thickness of the quantum well layer is 50 μs, and the thickness of the second sub quantum well layer is shown in FIG. This is the result of calculating the spontaneous emission rate while varying the thickness Lw1 of the first sub quantum well layer having the band gap relatively smaller than the band gap.

Referring to FIG. 5, when the thickness Lw1 of the first sub quantum well layer having a relatively small band gap is smaller than the thickness Lw2 of the second sub quantum well layer having a relatively large band gap, the spontaneous emission rate is It can be seen that the increase.

Specifically, it can be seen that the spontaneous emission rate is excellent when the thickness Lw1 of the first sub quantum well layer is 8 kW to 22 kW.

Since the thickness Lw2 of the second sub quantum well layer is obtained by subtracting the thickness Lw1 of the first sub quantum well layer from the thickness of the quantum well layer, the thickness Lw1 of the first sub quantum well layer and the second sub quantum well layer The ratio of the thickness Lw2 of the layer has excellent spontaneous emission rate in the range of 8/42 to 22/28.

In particular, when the thickness Lw1 of the first sub quantum well layer is 15 μs and the thickness Lw2 of the second sub quantum well layer is 35 μm, that is, the thickness Lw1 and the second sub quantum of the first sub quantum well layer It can be seen that the spontaneous emission rate is maximum when the ratio of the thickness Lw2 of the well layer is 15/35.

Hereinafter, various embodiments of the present disclosure will be described.

(1) The semiconductor light emitting device according to claim 1, wherein the size of the first band gap is smaller than that of the second band gap, and the thickness of the first sub quantum well layer is thinner than that of the second sub quantum well layer.

As a result, the first sub quantum well layer and the second sub quantum well layer can contribute to light emission, and the spontaneous emission rate can be maintained excellent.

(2) The quantum well layer has a stepped band gap in the E-k space, wherein the semiconductor light emitting element is characterized in that it is.

(3) The first compound semiconductor is made of indium gallium nitride (InGaN), and the second compound semiconductor is made of gallium nitride (GaN).

(4) The first sub quantum well layer is formed of In (x) Ga (1-x) N, and the second sub quantum well layer is formed of In (y) Ga (1-y) N, x and y Is a semiconductor light emitting device, characterized in that different from each other.

(5) x has a value of 0.15 ≦ x ≦ 0.25, and y has a value of 0 <y ≦ 0.075.

As a result, the light emitting characteristics of the semiconductor light emitting device emitting a wavelength corresponding to blue light can be improved, and the band gap difference between the second sub quantum well layer and the barrier layer becomes too large to prevent the strain dispersion effect from being reduced. Can be.

(6) The ratio a / b of the thickness a of the first sub quantum well layer and the thickness b of the second sub quantum well layer has a value of 0.19 ≦ a / b ≦ 0.79. Semiconductor light emitting device.

Thereby, the spontaneous release rate can be kept excellent.

According to one semiconductor light emitting device according to the present disclosure, the first and second sub quantum well layers having different band gaps have a quantum well layer having a stepped band gap in the Ek space, and such a stepped band gap. By the electrons and holes are constrained in a position closer to the space can be improved light transition characteristics.

In addition, according to another semiconductor light emitting device according to the present disclosure, since the quantum well layer 113 includes two sub quantum well layers 113, the lattice constant difference between the barrier layer 123 and the quantum well layer 113 may be reduced. It is possible to obtain the effect that the generated strain is dispersed, the dispersion of the strain may have the advantage that the piezo electric field is reduced and thus the light transition characteristics are improved.

In addition, according to another semiconductor light emitting device according to the present disclosure, since the quantum well layer of the three-element film made of InGaN is used, growth conditions are easier than that of the four-element film barrier layer.

Claims

A first semiconductor layer having a first conductivity;

A second semiconductor layer having a second conductivity different from the first conductivity;

And an active layer interposed between the first semiconductor layer and the second semiconductor layer.

Active layer,

A quantum well layer formed of the first compound semiconductor; And

A barrier layer formed of a second compound semiconductor;

Quantum well layer,

A first sub quantum well layer having a first band gap; And

And a second sub quantum well layer having a second band gap having a different size from the first band gap.
The method according to claim 1,

The quantum well layer has a stepped band gap in the E-k space, the semiconductor light emitting device.
The method according to claim 1,

The size of the first bandgap is smaller than the size of the second bandgap,

The thickness of the first sub quantum well layer is thinner than the thickness of the second sub quantum well layer.
The method according to claim 1,

The first compound semiconductor is made of indium gallium nitride (InGaN),

The second compound semiconductor is made of gallium nitride (GaN).
The method according to claim 1,

The first sub quantum well layer is formed of In (x) Ga (1-x) N,

The second sub quantum well layer is formed of In (y) Ga (1-y) N,

x and y are different from each other.
The method according to claim 5,

x has a value of 0.15≤x≤0.25,

y has a value of 0 <y≤0.075.
The method according to claim 1,

The size of the first bandgap is smaller than the size of the second bandgap,

The ratio (a / b) of the thickness (a) of the first sub quantum well layer and the thickness (b) of the second sub quantum well layer has a value of 0.19 ≦ a / b ≦ 0.79. .
The method according to claim 3,

The first compound semiconductor is made of indium gallium nitride (InGaN),

The second compound semiconductor is made of gallium nitride (GaN).
The method according to claim 8,

The first sub quantum well layer is formed of In (x) Ga (1-x) N,

The second sub quantum well layer is formed of In (y) Ga (1-y) N,

x and y are different from each other.
The method according to claim 9,

x has a value of 0.15≤x≤0.25,

y has a value of 0 <y≤0.075.
The method according to claim 9,

The ratio (a / b) of the thickness (a) of the first sub quantum well layer and the thickness (b) of the second sub quantum well layer has a value of 0.19 ≦ a / b ≦ 0.79. .
The method according to claim 9,

The first semiconductor layer is provided as an n-type contact layer for injecting electrons into the active layer

The second semiconductor layer is provided as a p-type contact layer for injecting holes into the active layer,

The quantum well layer has a stepped band gap in the E-k space,

The ratio (a / b) of the thickness (a) of the first sub quantum well layer and the thickness (b) of the second sub quantum well layer has a value of 0.19 ≦ a / b ≦ 0.79. .