JPH04188679A - Semiconductor light-emitting element - Google Patents

Abstract

PURPOSE:To enable a blue light emitting element of DH structure to be obtained by a method wherein Zn1-xCdxS multilayer structured layers different in composition ratio (x) are formed on a singlecrystal substrate, an active layer containing Zn and Se is provided thereon, and Zn1-xCdxS multilayer structured layers are formed thereon. CONSTITUTION:A distortion superlattice layer composed of Zn1-xCdxS multilayer structured layers 22 different in composition ratio (x) is formed on a single- crystal substrate 21, an active layer 23 containing Zn and Se is provided thereon, and a Zn1-xCdxS multilayer structured layer 24 is formed thereon, where the multilayer structured layers 22 and 24 are made to function as clad layers. The compositional ratio Zn:Cd of ZnCdS is so set as to enable the average lattice constant of the distortion superlattice layers 22 and 24 to be nearly coincident with that of the active layer 23 and the distortion layers 22 and 24 to have a larger forbidden width than the active layer 23. By this setup, a double-hetero structure (DH structure) can be realized, and in result a blue light emitting element can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor light emitting device having a blue light emitting function and made of a II-VI group compound semiconductor material.

[Conventional technology]

As a conventional light emitting element with a blue light emitting function, SiC
There is a pn junction type light emitting diode using (in the latest report, Y, Matsushita et al., J.
pn.

J, Appl, Phys, 29 (1990) L343)
, SiC cannot form a double heterostructure (hereinafter abbreviated as DH structure) and is an indirect transition type, so its luminous efficiency is low and it cannot be converted into a laser.

In addition, there are MIS type light emitting diodes in ZnS and ZnSe (for example, J, 1. Pankove,
J. Lumm.

7 (1973) 195. M.D.Ryall and
J, W, A11en, J, Phys.

Chem.
EJ, Quantum Electron, QE-
14 ('1978) 358), these also cannot be made into practical lasers because of their low luminous efficiency.

[Problem to be solved by the invention]

As described above, a current injection DH structure type blue light emitting device has not been realized at this time, and this remains a challenge for the future.

The present invention has been made in view of the above circumstances, and uses ZnSe or ZnSSe, which is a semiconductor material having a forbidden band width corresponding to culprit luminescence, as an active layer (emitting layer), and a cladding layer consisting of ZnSe or GaAs and a lattice. The object of the present invention is to provide a gastrochromic light-emitting element having an H structure, which satisfies the requirements of being able to match and ensure a difference in forbidden band width ΔEg and a difference in refractive index Δn, has high current injection efficiency, can be made into a laser, and has an H structure.

[Means to solve the problem]

In order to achieve the above object, the semiconductor light emitting device according to claim 1 of the present application provides Zn+-x with different composition ratios X on a single crystal substrate.
forming a strained superlattice layer consisting of a cdxs multilayer structure layer, forming an active layer containing at least Zn and Se on top of the strained superlattice layer;
Above that, the Zn1. ,□,Cd.

It is characterized by forming an S multilayer structure layer, and this multilayer structure layer functions as a cladding layer.

Further, the semiconductor light emitting device according to claim 2 of the present application includes Zn1-XCdX5 and Znt-YCdYS (x
>y) are alternately stacked to form a superlattice cladding layer, an active layer is formed on the superlattice cladding layer, and Z
It is characterized by forming an nCd5/ZnCd5 strained superlattice cladding layer.

A semiconductor light emitting device according to claim 3 of the present application is characterized in that, in the semiconductor light emitting device according to claim 2, an n-type ZnSe buffer layer is provided between the substrate and the superlattice cladding layer.

Hereinafter, the semiconductor light emitting device of the present invention will be explained in detail.

In a current injection semiconductor light emitting device having a double heterostructure (DH structure), the material forming the cladding layer has a larger forbidden band width and smaller refractive index than the material forming the active layer, and both lattice constants must approximately match each other.

Therefore, in order to achieve the above object, a semiconductor light emitting device according to the present invention is manufactured using a ZnSe (100) substrate or a GaAs
(100) using ZnSe or ZnSS on the substrate.
Above and below the active layer consisting of Z, there are two types of Z with different composition ratios.
n+-xcdx S, Zn,-ycdys (x>
y) sandwiched between alternately laminated strained superlattice layers,
It is characterized by using the strained superlattice layer itself as a cladding layer.

Note that in this cladding layer, quantum effects such as quantum confinement effects do not need to be significant.

Here, FIG. 1 is a cross-sectional view of the strained superlattice layer.

In FIG. 1, Zn layers with different composition ratios are stacked alternately.
When the layer properties 2 of the +-xcd13 layer 11 and the Zn+-ycdys layer 12 are Lx and Ly (Lx>Ly), respectively,
The relationship between the layer thickness (Lx, Ly) that functions as a cladding layer and the composition ratio (x, y) is derived as follows. First of all,
The layer thickness ratio 2 of the superlattice is defined as z=Lx/(Lx+Ly).

Consider approximating the actual lattice constant of the strained superlattice by the average lattice constant aAV% and matching it to the lattice constants of the substrate and the active layer or their averages. In addition, a(Zn+-xC
dxS) and a(Znl-YCdYS) represent lattice constants.

The relationship z(x-y)+y=u (constant)...(1) holds between the layer thickness ratio 2 and the composition (x, y), where U is Zn and uCduS is ZnSe or Ga.
u=(a'
azns)/(acds azns) (where a
= a zns, =5.6687 people, or a =
acaAm=5.653 is the lattice constant to be matched. az
, s=5.4093 people, acas=5.832 people), and u=0.61 for ZnSe and u=0.58 for GaAs.

Considering the stability of the strained superlattice layer, it depends on the difference in lattice constant determined by the composition ratios X and y, but the thicker Zn1-xc
The dzs layer has (L y <) L x < 300 people, and the thinner Zn+-YCdYS layer has 20 people <Ly < 100 people.

If the film thickness ratio 2 of the two layers is large (Lx>>Ly), Zn1
, :The ycdys layer becomes relatively thin, but for example, when z=
When L x + Ly is 0.9 and L y is 200 people, Ly = 20 people. This corresponds to the thickness of four unit cell layers of Zr++-ycdys, which makes it difficult to form a film of ZnCd5 mixed crystal, and the crystallinity worsens with respect to doping, making it impossible to form a strained superlattice.

Therefore, in consideration of film formation and doping, the layer thickness ratio is limited to approximately 20 <Ly and z<0.9 (2).

Next, the composition ratio is such that the lattice constant of Zn+-xCdxS is smaller than that of the active layer, and the difference in forbidden band width (Eg) ΔEx is larger, ΔEx=Eg(Zn+-xCdxS) Eg (active layer) ≧0, but since the Zn+-ycdys layer is more involved in carrier confinement, it can function even at ΔEx>-0.2 eV, so when the active layer is ZnSe, 0.61< x <0 .87...(3
) or Zn5o, osSe lattice matched to GaAs
When o, *<, 0, 58< x <0.82...(4
). Furthermore, carriers are more effectively confined when △Ex>-0,1eV, and Zn
For Se active layer, 0.61<x<0.77...(5
) for ZnSo, ogSeo, *4, 0.58<
x <0.72 (6).

The composition ratio y can function as a laser if the difference ΔEy between the forbidden band width between Zn1-ycdys and the active layer is 0.2 eV or more, and y<0.5 (7).

In the case of GaAs/AlGaAs LD, △Eg>0.3
Since good luminous efficiency is obtained when eV, ΔEy>0.
More preferably 3 eV, 3<0.4
...(8), but in order to ensure the potential barrier (ΔEc) in the conduction band, it is more desirable that A〈o,3...(9).

Next, the above results will be explained using the second factor.

Figure 2(a) shows the strained superlattice layer of ZnSe, and Figure 2(b) shows the strained superlattice layer of GaAs, Zn5o, esSe.
This is a case where matching is made to 5,653 people of o and sa. Here, the straight lines A, I, AS, AT, and AU have layer thickness ratios z=0.9, z=0.8, z=0.7, and z=0.6, respectively, as examples.
This is the relationship between X and y in equation (1) when given, and equation (2
) condition z<0.9 corresponds to the upper right region of straight line AI. Furthermore, AE corresponds to the lower limit of X in inequalities (3) to (6), MQ corresponds to the upper limit of composition ratio X in inequality (3) or (4), and JL corresponds to the composition ratio X in inequality (5) or (6). corresponds to the upper limit of Also BM, CN.

DP is the allowable range of 0 composition corresponding to the upper limit of the composition ratio y in inequalities (7), (8), and (9), respectively, is the four-sided shadow area F
MQI, but the four-sided shadow region GNQI is a more suitable composition region. Furthermore, the quadrilateral shadow region HKLI is the best region.

Within these regions, assuming that the refractive indices of ZnSe and CciS (zincite type) are similar, ZnS and ZnS
Considering the refractive index difference of e, the refractive index difference between the active layer and the cladding layer can be ensured to be at least 0.1 or more.

If the thickness of the strained superlattice layer per period is 200, then M
BE(Molecular Beam Epitaxy)
) and the range of cladding that functions as a cladding, it is sufficient that the entire cladding layer has a thickness of about 1 μm.
Lamination of 0 to 100 cycles is suitable.

[For production]

As described above, the semiconductor light emitting device having the structure based on the present invention has the strained superlattice 7. nH-1cdz S / Zn+-ycdv S
The average lattice constant of ZnSe or ZnSSe of the active layer is made to almost match that of ZnSe or
Zn and Cd of ZnCd5 have a forbidden band width greater than +14.
By selecting the composition ratio (x>y) and the thicknesses Lx and Ly of the two layers, it becomes possible to configure a DH structure, and it becomes possible to realize a semiconductor light emitting device having a blue light emitting function.

〔Example〕

Hereinafter, the present invention will be explained in detail based on illustrated embodiments.

Embodiment 1 FIG. 3 is a perspective view of a light emitting device showing a first embodiment of the present invention, and the internal structure of the device is shown in a broken section.

In FIG. 3, the semiconductor light emitting device according to the present invention has n
Zn is deposited on a GaAs (100) substrate 21.

An n-type superlattice cladding layer 22 in which Cd, S and Zn+-ycdys (x>y) are alternately laminated, an n-type ZnSe active layer 23, a p-type ZnCd5/ZnCd5 strained superlattice cladding layer 24, a p-type ZnSe cap layer 25 , a 5iOz insulating layer 26 with striped grooves and an exposed cap layer;
A p-type ohmic electrode (A, u) 27 is sequentially laminated on top of the GaAs substrate 21, and an n-type ohmic electrode (AuGe/Ni/Au) 2g is formed on the back surface of the GaAs substrate 21.

In addition, each epitaxial layer has the following characteristics: n-type strained superlattice layer 22 - 1μm n-type ZnSe active layer 23 - 0.5μm p-type strained superlattice layer 24 - 1μm p-type cap layer 25 - 1μm Laminated by MEE method, Si
o. The insulating layer 26 is formed by plasma CVD.

Here, the n-type strained superlattice layer 22 is made of Zno, 5Cdo, and S to match the average lattice constant of GaAs and ZnSe.
154 people, Zno, tscdo, 25 S, 46 people
A person stacks the layers 50 times. These conditions are included in the best composition region of FIGS. 2(a) and 2(b). Also pff
The i-strained superlattice layer 24 has Z no, which matches ZnSe,
s Cdo, 7 S 160 people, Zno, tscd
a. 25S was laminated alternately for 50 cycles by 40 people.

Finally, end faces 30 are formed at the front and rear sides perpendicularly to the stripes.

With the element structure shown in FIG. 3, as a result of passing current through the upper and lower electrodes, a wavelength corresponding to the forbidden band width of ZnSe is transmitted from the active layer 23 in the direction 31 perpendicular to the end face 30 with a differential efficiency of 0.1 W/A. Oscillation of approximately 470 nm was obtained.

Soumata Kamasa: The second embodiment has a structure in which the n-type GaAs substrate 21 in the first embodiment is replaced with an n-type ZnSe (100) substrate. In addition, only the structure of the strained superlattice of the cladding layer differs from Example 1, and 160 Zno, 5Cdo, 7S, and 40
Human Zno, tbcda, and zs S are stacked alternately for 50 cycles.

According to the device structure of this second embodiment, by replacing the substrate, restrictions on the growth temperature in consideration of mutual diffusion at the interface between the substrate and the epitaxial growth layer are alleviated, and the original device structure can be restored under more optimal conditions. possible, oscillation wavelength 4.70n
m, the light emitting output was increased compared to the element of Example 1, and the differential efficiency was twice as high as 0.2 W/A.

Embodiment 3 FIG. 4 is a perspective view of a light emitting device showing a third embodiment, and this embodiment has an n-type ZnSe buffer layer 29 between the GaAs substrate 21 and the n-type cladding layer 22 in FIG. The device can be configured by giving the same parameters as in Example 2, or by using Z as a buffer layer.
An n5wSe+-w gradient layer (O≦W≦0.06) may be provided to match the superlattice layer to ZnSe. In this case, dislocations and defects at the substrate interface can be suppressed, and the crystal of each epitaxial layer Improved performance and differential efficiency of 0.15
A current injection efficiency of W/A could be obtained.

A fourth embodiment of the present invention is made of GaAs (100)
In the structure of FIG. 3 in Example 1 using a substrate, GaA is used instead of ZnSe in the active layer 23 and cap layer 25.
Zn5o, ogSeo, which matches the lattice constant of the s substrate
This is the structure replaced with *<.

With the change of lattice constant, the strained superlattice layer becomes 146 Zn
o, 5cdo, 7 S, and 54 Zno, ts
It is formed by stacking cdo and zss alternately for 50 periods.

Furthermore, as in the structure shown in FIG. 4 in Example 3, by inserting a ZnS0°6Seo, s4 buffer layer between the substrate and the n-type cladding layer to suppress the diffusion of Ga and As into the superlattice layer, The conduction characteristics were improved, and with this device structure, oscillation of about 460 nm, which corresponds to the forbidden band width of ZnSSe, was obtained, and the differential efficiency was improved to 0.3 W/A.

Although Examples 1 to 4 have been described above, it goes without saying that the conductivity types p and n may be replaced in the above examples.

〔Effect of the invention〕

As explained above, in the element structure according to the present invention, Z
By forming a cladding layer using a strained superlattice for the r+Se or ZnSSe active layer, a DHW structure becomes possible, and a semiconductor light emitting device having a blue light emitting function can be realized.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the cross section and layer thickness of a superlattice layer of a semiconductor light emitting device according to the present invention. Figure 2 shows the superlattice layer Zn+-xCdxS/ in the present invention.
It is a graph showing the relationship and tolerance range of composition x, y and film thickness ratio 2 of Zn+-ycdvs, and the figure (a) is a graph showing the tolerance range of ZnSe.
When matching to 5.6687 people, the same figure (b) is Ga
This is a case of matching to 5.653 people of As (ZnSo, osSeo, sa). FIG. 3 is a perspective view of a semiconductor light emitting device showing the device structure in Examples 1, 2.4 of the present invention. FIG. 4 is a perspective view of a semiconductor light emitting device showing the device structure in Example 3 of the present invention. 11′-”Zn+-xcdxs layer, 12=・Zn+-y
CC1ys layer, 21-/-n type substrate (GaAs or Z
nSe), 22-n type n+-xCdxS/Zn+-,
vCdyS strained superlattice cladding layer, 23... n-type active layer (n-type ZnSe or n-type ZnS Se), 21-
・p-type Zn1-xCdyS/Zn+-yCdYS strained superlattice cladding layer, 25... p-type cap layer (n-type Z
nSe or p-type ZnS Se), 26-insulating layer (
SxOz), 27---p-type Ohmig electrode (Au)
, 28--n type ohmic electrode (AuGe/Ni/Au
), 29... Buffer layer (n-type ZnSe or n-type ZnSSe graded layer), 30... Light emitting element end face (cleavage plane), 31... Emitted light emission direction. Goyu”. ’I,”ν

Claims (1)

[Claims] 1. Zn_1_-_x with different composition ratios x on a single crystal substrate
A strained superlattice layer consisting of a Cd_xS multilayer structure layer is formed, an active layer containing at least Zn and Se is formed on top of the strained superlattice layer, and the Zn_1_-_xCd_xS multilayer structure layer is formed on top of the active layer, and this multilayer structure layer is A semiconductor light emitting device characterized by functioning as a cladding layer. 2. Zn_1_-_xCd_xS and Z on single crystal substrate
n_1_-_YCd_YS (x>y) are alternately stacked to form a superlattice cladding layer, an active layer is formed on the superlattice cladding layer, and a ZnCdS/ZnCdS strained superlattice cladding layer is formed on the active layer. A semiconductor light emitting device characterized by: 3. The semiconductor light emitting device according to claim 2, wherein a ZnSe buffer layer is provided between the substrate and the superlattice cladding layer.