JPH05291617A - Semiconductor light emitting device - Google Patents

Abstract

PURPOSE:To enable electrons-holes to be confined in a light emitting layer effectively by giving compression or tensile strain into a barrier layer. CONSTITUTION:GaP, GaAs, Si, ZnSe or the like, preferably GaP and GaAs, can be utilized as a substrate 10. A light emitting layer 13 consists of a known composition of (AlyGa1-y)mIn1-yP. A barrier layer 14 is formed in adjacency to the light emitting layer 13: its composition is (AlnGa1-n)mIn1-mP(0<=m, n<=1), and the barrier layer 14 includes compression or tensile strain. The load of compression or tensile strain to the barrier layer sets a composition of the barrier layer so that a lattice constant of the barrier layer bulk may be different from a lattice constant of the base, and controls the barrier layer thickness and crystal growth conditions so that a lattice constant of the barrier layer may be matched with a lattice constant of the base for crystal growth. This process enables electrons-holes to be confined in a light emitting layer effectively. Therefore, this device can contribute to efficiency of yellow-green semiconductor light emitting device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device mainly used for display.

[0002]

2. Description of the Related Art Conventional materials for semiconductor light emitting devices are
lGaAs-based mixed crystals have been widely used. However, when a light emitting device is manufactured using this material system, there is a problem that the efficiency is reduced at a wavelength shorter than 660 nm (red). AlGaInP-based materials have been energetically developed to overcome this problem, but the wavelength is 590 nm (yellow).
Higher efficiency has not been obtained at shorter wavelengths. Shorter wavelength semiconductor light emitting device (light emitting diode: LE
As D), there is a GaP type, which has a wavelength of 565 nm.
(Yellowish green) is obtained, but in the efficiency compared with each wavelength showing the highest brightness, AlGaAs system or AlGa
It is extremely worse than the InP type.

[0003]

GaP yellow-green LED
The following two points can be considered as the causes of the inefficiency of. GaP is an indirect transition and is doped with an impurity N that serves as an emission center, but the emission efficiency is inferior to that of the direct transition. Since a normal GaP light emitting device has a homojunction structure and does not have a structure for confining carriers (electrons / holes) in the light emitting layer, carriers overflow from the light emitting layer and make a non-light emitting transition outside thereof. Since this is an essential problem, many attempts have been made to solve it by using other wide band gap direct transition light emitting materials, but at the present time, there are some other problems and high efficiency. Things have not been obtained. Has a wider band gap than GaP,
It has been attempted to confine carriers and achieve high efficiency by using AlP that is lattice-matched to P as a carrier barrier layer (hereinafter, a layer having such a function will be simply referred to as a barrier layer). Not obtained. This interpretation was attributed to the fact that AlP is very easily corroded by air, and good quality crystals cannot be obtained, but the latest research using superlattices revealed that there are more fundamental problems. became.

The problem is that at the GaP-AlP interface,
As shown in FIG. 7A, the confinement of holes in GaP can be obtained, but the confinement structure of electrons in GaP cannot be obtained. A heterojunction structure in which only one of electrons and holes is confined in this way is called Type II. On the other hand, at the GaAs-AlAs interface, as shown in FIG.
As shown in (b), both electrons and holes are confined on the GaAs side. Such a heterojunction structure will be called type I.

[0005]

SUMMARY OF THE INVENTION The present invention, light-emitting layer on the substrate _{(Al y Ga 1-y)} X In 1-X P (0 ≦ x, y ≦
In a semiconductor light emitting device in which a pn junction having the composition of 1) is formed, a barrier layer is formed adjacent to the light emitting layer,
Its composition is (Al _n Ga _1-n ) _m In _1-m P (0 ≦ m,
There is provided a semiconductor light emitting device characterized in that n ≦ 1) and that the barrier layer has compression or tensile strain.

The substrate of the present invention is made of GaP, GaAs, S.
i, ZnSe and the like can be used, and GaP and Ga are preferable.
It is As. The light-emitting layer is known _{(Al y Ga 1-y)} X In
_{It has} a composition of _1-XP . The composition of the barrier layer is (Al _n Ga _1-n ) _m In _1-m P, and the range of m and n is 0 to 1. Further, the range of m is preferably 0.4 to 1 when the substrate is GaP, and preferably 0.4 to 0.8 when the substrate is GaAs.

The thickness of the strain barrier layer may be set as large as possible within a critical film thickness range where lattice defects do not occur. However, the critical film thickness decreases in inverse proportion to the amount of strain. The range is generally 1000 Å or less, preferably 3
It is 00Å. As a method for forming the barrier layer, an MBE method (molecular beam growth method), a VPE method (vapor phase growth method), an LPE method (liquid phase growth method), or the like can be applied.

The load of compressive or tensile stress on the barrier layer is set so that the lattice constant of the bulk of the barrier layer is different from the lattice constant of the underlayer, and the lattice constant of the barrier layer is set to the lattice constant of the underlayer. So that they will fit together and grow crystals,
It is provided by controlling the thickness of the barrier layer and the crystal growth conditions. According to the present invention, in the light emitting element using the AlGaInP-based material for the light emitting layer, the heterojunction using the material in which the barrier layer and the light emitting layer are lattice-matched is the type II or the type I in which the desired barrier height is not obtained. In case,
In order to confine carriers, the portion of the barrier layer adjacent to the light emitting layer is formed by a strained layer that is a thin film that does not cause lattice defects and does not form a lattice junction with the light emitting layer, thereby providing a higher barrier barrier. To realize a type I heterojunction having the above structure and improve the light emission efficiency.

The light emitting layer may be a direct transition or an indirect transition,
It is possible to add or not to add an impurity that becomes a luminescence center.

[0010]

The operation will be described by taking as an example the case where GaP is used as the light emitting layer with an AlGaInP-based material. The material that lattice-matches with GaP is Al _x Ga _{1 -X} P (0 ≦ x ≦
In 1), when this material is used as a barrier layer, the heterojunction with the GaP light emitting layer is of type II no matter how many x, no electrons can be confined, and the luminous efficiency is of type I. Significantly inferior. Therefore, although the condition for lattice matching is not satisfied, it is considered whether or not a type I heterojunction may form with the GaP light emitting layer when the barrier layer is AlGaInP.

In order for the junction to be type I, the barrier layer
Band gap is larger than the band gap of the light emitting layer
In addition, the conduction band level of the barrier layer depends on the conduction band level of the light emitting layer.
Must be higher than the bell. The conduction band level is Ga_0.5I
n_0.5Relative value to P ΔEc₀Will be represented by. Figure
8, the horizontal axis is the lattice constant and the vertical axis is the band gap energy
And Ga_0.5In _0.5ΔEc based on P (point U)
₀Shows the phase diagram of the AlGaInP system with the contour lines added.
You ΔEc₀Is AlP (point Q), InP (point T)
Each has a minimum value and Ga_0.8In_0.P (point V) and Al
_0.4In_0.6It becomes higher on the line connecting P (point S), especially A
l_0.4In_0.6It has a maximum value at P (point S). Area PQS
V is an indirect transition region, and region STV is a direct transition region.
Barrier layer that is a type I junction to GaP (point P)
Is ΔEc equal to GaP (point P)₀Below the line PR
Side, line PW with a bandgap equal to GaP (point P)
Must be above. This condition holds at the same time
The region PRSW is the composition of the strain barrier for GaP.
It is a suitable range. Note that the quantum effect and
And bandgap changes due to strain are not taken into account
Yes. Strictly considering these points, the outside of the region PRSW
Can be used as a strain barrier even at (eg point V)
There are cases where

Generally, a heterojunction which does not satisfy the lattice matching condition has many lattice defects and is therefore unsuitable for use in a light emitting device. However, in a very thin film, the lattice defects are generated in the presence of compressive (or tensile) stress. You can prevent it from happening. The maximum film thickness that can exist without the occurrence of lattice defects is, for example, InGaA grown on GaAs.
In the s thin film, when the strain amount is 1%, it is about 90Å, and decreases in inverse proportion to the strain amount. The strain barrier layer is composed of such a thin film.

[0013]

The present invention will be described in detail below based on examples.

Example 1 In Example 1, as shown in the explanation of the operation, GaP (FIG.
Point P) is used as a light emitting layer, and (Al _0.3 Ga _0.7 ) _0.8 In
_0.2 P (point X) was used as the p-side strain barrier layer. A cross-sectional view of the device is shown in FIG. MOCVD type (Metal Organic Chem
n-type GaP buffer layer 11 on the n-type GaP substrate 10 by ical vapor deposition (metal organic chemical vapor deposition).
Undoped Al _0.2 Ga _0.8 P hole barrier layer 12, N
Doped GaP light emitting layer 13, undoped (Al _0.3 Ga
_0.7 ) _0.8 In _0.2 P strain barrier layer 14 (compressive stress, thickness 70Å), p-type Al _n Ga _1-n P graded band gap layer 15 (n changes from 0.1 to 0), p-type G
The aP cap layer 16 is grown. A back electrode 17 and a front electrode 18 are formed on a part of each of the back surface of the substrate and the epitaxy surface.

In this element, since the substrate 10 and each layer are transparent with respect to the emission wavelength, light is emitted from the portions not covered by the electrodes on the front and back surfaces and the side surfaces. The wavelength of this device is 565 nm (yellowish green), the external quantum efficiency is 1.5%,
External quantum efficiency of 0.3% in conventional homojunction LED
Was about 5 times. A band energy diagram of the device at the time of current injection is shown in FIG. Efe is the pseudo-Fermi level of electrons and Efh is the pseudo-Fermi level of holes, and the difference between them is eV (e is the elementary charge amount, V is the applied voltage). n
Focusing on the electrons injected from the mold substrate 10 and flowing in the conduction band, the conduction band is from the n-type GaP buffer layer 11 to the n-type Al.
_Although it falls down to the _0.2 Ga _0.8 P hole barrier layer 12, since there are no holes in this region, electrons are saturated and injected into the GaP light emitting layer 13. Strain barrier layer 1
Therefore, most of the electrons do not get over this barrier at room temperature. On the other hand, the holes injected into the p-type GaP cap layer enter the p-type graded barrier layer 15,
It falls into the strain barrier layer 14. Here, since there are no electrons, the holes further proceed to the light emitting layer 13 and are radiatively or non-radiatively recombined with the electrons.

The strain of each layer is shown in FIG. A strong compressive strain is applied only to the strain barrier layer 14, and no strain occurs in other portions. The following modifications are possible for this embodiment. Al _0.2 Ga _0.8 P hole barrier layer 12
May be n-type or i-type (undoped). (Al _0.3
The Ga _0.7 ) _0.8 In _0.2 P strain barrier layer 14 may be p-type or i-type (undoped).

The n-side barrier layer 12 may also be a strain barrier layer. For example, (Ga _0.5 Al _0.5 Ga _0.5 ) _0.8 In
_{At 0.2} P, since ΔEc ₀ is equal to that of the GaP light emitting layer 13, there is no electron drop and it functions as a barrier layer against holes. The p-type graded barrier layer 15 may be omitted, and the p-type cap layer 16 and the strain barrier layer 14 may be in direct contact with each other.

The emission center impurities to be doped into the light emitting layer 13 are Bi, Zn and O, Zn and S, Zn and S, in addition to N.
e, Zn and Te, Mg and S, Mg and Se, Mg and Te, etc. may be used, and impurities may not be contained at all. The strain barrier layer 14 may be GaInP containing no Al. For example Ga _{0. 1} In _0.2 P strained barrier layer 1
When 4 ″ is used, the band gap is slightly smaller than that of GaP, and it seems that light absorption or the like occurs, which causes inconvenience, but since the strain barrier layer is extremely thin, the quantum effect causes the hole level to be quantum. In addition, since the effect of increasing the band width and the band expansion effect due to the compressive strain are generated, the efficiency is not particularly reduced, and since highly corrosive Al is not used, it is advantageous in terms of reliability.

Example 2 A sectional view of the device is shown in FIG. P by MOCVD method
A p-type Al _n Ga _1-n P graded bandgap layer 21 (n changes from 0 to 0.5) and an undoped Al _0.75 In _0.25 P strain barrier layer 22 on the Ga Ga substrate 20.
(Compressive stress state, thickness 30Å), N-doped Al _0.5 Ga
_0.5 P emission amount 23, undoped Al _0.8 In _0.2 P strain barrier layer 24 (compressive stress, thickness 50Å), p-type Al _n G
a _1-n P graded barrier layer 25 (n is 0.5 to 1)
Until the p type AlP cap layer 26 is grown. Further, a SiO ₂ protective layer 27 is formed by a sputtering method, and then the protective layer 27 is partially removed.
Then, the back surface electrode 29 is formed on the back surface of the substrate.

In this element, since the substrate 20 absorbs the emission wavelength, the light is emitted from the side surface as well as a part of the side surface. The emission wavelength was 540 nm (green).

Example 3 In Example 3, a strain barrier layer was applied to a light emitting device in which a light emitting layer was formed of AlGaInP which was a direct transition region. G
Lattice-matched to aAs (Al _n Ga _1-n ) _0.5 In _0.5
ΔEc ₀ of the P system is ₀ , +0.19, +0.12 eV for each scene of x = 0, 0.7, 1 and x
= 0.7, ΔEc ₀ becomes maximum. On the other hand, in order to realize green light emission, n of the light emitting layer needs to be about 0.6, and ΔEc ₀ thereof is +0.16 eV. Therefore, even if a system of n = 0.7 is used as the barrier layer, the conduction band is decreased. Only 0.03 eV can be obtained as a barrier.

Al _0.4 In _0.6 P as a strain barrier layer
Using (S in FIG. 8), ΔEc ₀ is +0.22 eV.
(Estimated value), so 0.06e as a conduction band barrier
V will be obtained. A cross-sectional view of the device is shown in FIG.
By the MOCVD method, p
Type (Al _x Ga _1-x ) _0.5 In _0.5 P graded band gap layer 31 (x changes from 0 to 0.7), undoped Al _0.4 In _0.6 strain barrier layer 32 (compressive stress state, thickness 80 Å), Undoped (Al _0.4 Ga _0.6 )
_0.5 In _0.5 P light emitting layer 33, n-type (Al _0.5 Ga _0.5 ).
_0.6 In _0.4 P strain barrier layer 34 (tensile stress state,
Thickness 60 Å), n-type Al _0.5 In _0.5 P barrier layer 35,
n-type (Al _n Ga _1-x ) _0.5 In _0.5 P graded bandgap layer 36 (x changes from 1 to 0), n-type G
The aAs cap layer 37 is grown. Surface electrode 3 on it
8 is formed, 38 is partially etched, and the n-type graded band gap layer 36 and the n-type cap layer 37 are partially removed by using 38 as a mask. A back surface electrode 39 is formed on the back surface of the substrate.

A band energy diagram of the device is shown in FIG.
By using the graded band gap layers 31 and 36, respectively, the valence band at the interface with GaAs
The conduction band notch is suppressed. The strain barrier layer 32 confines electrons and the strain barrier layer 34 confines holes in the light emitting layer 33. By using the strain barrier layer 34, a notch in the conduction band with the barrier layer 35 does not occur.

In this element, since the substrate 30 absorbs the emission wavelength, light is emitted from the surface and the side surface. The emission wavelength was 557 nm (green). In the present embodiment, the light emitting layer has a direct transition, but since it is close to an indirect transition, the emission brightness is increased by doping an impurity (N or the like) serving as an emission center. However, in that case, the emission wavelength becomes slightly longer.

[0025]

EFFECTS OF THE INVENTION AlGaInP semiconductors that can be used for red to yellow to green light emitting devices with a wide bandgap are particularly suitable for short wavelength light emission from yellow to green. It becomes difficult to confine the holes. In the present invention, electrons and holes can be effectively confined in the light emitting layer by using a strained layer for the barrier layer. Therefore, the present invention is particularly useful for increasing the efficiency of yellow to green semiconductor light emitting devices.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a semiconductor light emitting device of Example 1.

FIG. 2 is an energy band diagram and a strain amount diagram of the semiconductor light emitting device of Example 1.

FIG. 3 is a sectional view of a semiconductor light emitting device of Example 2.

FIG. 4 is an energy band diagram of the semiconductor light emitting device of Example 2.

FIG. 5 is a sectional view of a semiconductor light emitting device of Example 3.

6 is an energy band diagram of the semiconductor light emitting device of Example 3. FIG.

FIG. 7 is an explanatory diagram of type II and type I band discontinuities in a heterojunction.

FIG. 8 is an explanatory diagram of the relationship between the lattice constant and the band gap energy of an AlGaInP-based material.

[Explanation of symbols]

10 n-type GaP substrate 11 n-type GaP buffer layer 12 AlGaP hole barrier layer 13 GaP: N light-emitting layer 14 AlGaInP strain barrier layer 15 p-type AlGaP graded bandgap layer 16 p-type GaP cap layer 17 front surface electrode 18 back electrode 20 p -Type GaP substrate 21 p-type AlGaP graded band gap layer 22 AlInP strain barrier layer 23 n-type AlGaP light-emitting layer 24 AlInP strain barrier layer 25 p-type AlGaP graded barrier layer 26 p-type AlP cap layer 27 SiO ₂ protective layer 28 surface electrode 29 Backside Electrode 30 p-type GaAs Substrate 31 p-type AlGaInP Graded Band Gap Layer 32 AlGaInP Strain Barrier Layer 33 AlGaInP Light Emitting Layer 34 n-type AlGaInP Strain Barrier Layer 35 n-type AlInP Rear layer 36 n-type AlGaInP graded band gap layer 37 n-type GaAs cap layer 38 surface electrode 39 back-surface electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuo Suga 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Hiroshi Nakatsu 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Incorporated (72) Inventor Osamu Yamamoto 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Prefecture

Claims (3)

[Claims] 1. A light-emitting layer on the substrate _{(Al y Ga 1-y)} X
In a semiconductor light emitting device in which a pn junction having a composition of In _1-X P (0 ≦ x, y ≦ 1) is formed, a barrier layer is formed adjacent to the light emitting layer, and the composition is (Al _n Ga _{1 -n)} is _{m in 1-m P (0} ≦ m, n ≦ 1), the semiconductor light emitting device characterized by having a compressive or tensile strain in the barrier layer. 2. The semiconductor light emitting device according to claim 1, wherein the composition of the substrate is GaP. 3. The substrate composition is GaAs.
The semiconductor light emitting device described in the item.