JPH01184972A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To decrease the effect of a barrier generated at an interface so as to decrease on operating voltage by a method wherein a super lattice layer and an intermediate band gap layer are provided between a clad layer large in a band gap and a contact layer small in a band gap. CONSTITUTION:A super lattice layer 16 provided with the same structured layer as a P-clad layer 15 and a P-intermediate band gap layer 17 are provided between the P-clad layer 15 and a P-GaAs electrode contact layer 18. The carrier concentration of the super lattice layer 16 and the intermediate band gap layer 17 are made higher than that of the P-clad layer 15. A P-super lattice layer and an intermediate band gap layer are formed as mentioned above, wherefore the height of the barrier at each interface can be decreased. And, as the P-electrode contact layer 18 can be doped in high concentration, the barrier can be decreased in height. By these processes, a semiconductor laser element low in an operating voltage and excellent in reliability can be obtained even if the element is a DH laser which has a large band gap difference between a clad layer and an electrode contact layer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a semiconductor laser with low previous voltage and high reliability.

(Prior Art) Semiconductor lasers having a double-hetero S structure have attracted attention as light sources for optical communication and optical processing.

InP f substrate by epitaxial growth method
G&AjP series and GaAjAa yarns have been put into practical use as m-vi semiconductor mixed crystal materials. Further, in recent years, progress has been made in the development of InGaAlP semiconductor lasers that use GaAs as a substrate and have a finely aligned lattice.

InGaAjP, which is lattice matched to caAas, has a band gap energy of about 1.9 to 2.35 eV, m-'v.
As a group compound W Tetarumoto mixed crystal, it has a relatively large casing. Therefore, by using it as the cladding layer material, carrier confinement and light confinement can be achieved even if a material with a large band gap is used as the active layer material. This makes it possible to oscillate at short wavelengths that have not been visible with the material systems that have been put into practical use so far. Such semiconductor lasers have many advantages over conventional ones - for example, they enable higher density recording when used as light sources for optical discs and audio/video discs. .

Also, ZuSe (:uQa) created on one GaAs board
Ss 6QJT1- 'l@, I -m -V1@O
By using four methods, it is possible to further shorten the wavelength of the semiconductor laser.

(Problems to be Solved by the Invention) In the semiconductor laser as described above, the following problems will be explained using a semiconductor laser having an InGaAjP8 cladding 1 as an example.

In order to increase the oscillation wavelength, it is necessary to make the band gap of active 1 and the band gap of cladding sufficiently large. To give an example from a practical standpoint such as low ft [iK style and high reliability], in order to set the oscillation wavelength to 620 nm, the band gap energy must be 2.0 e for the active 1.
It is desirable that the VDInGaAjP cladding 1 be a double heteroaha using JnQa-AlP% with a band gap energy of 2.35 eV.

Such double heterostructures can be used for metal pyrolysis removal (Met
alorganice Chemical 34apo
r Deposition: MOCVD hereafter) or single molecular beam epitaxy (Molecular Beam Epitaxy)
Epiaxy: Obtained by epitaxial growth on a GaAs4 plate from M8EH. In addition, when ILR implantation is performed on such a double heterostructure, one side is made conductive and the substrate is used as a four-pole contact field, rather than making the i-band conductive and providing an ohmic electrode. Current injection from the opposite side is achieved by providing a GaAs cap layer with conductivity opposite to that of the substrate on the crat layer and forming an electrode thereon to use it as an electrode contact layer. The following are the advantages of using this as an electrode contact layer.

That is, QaAs is crystalline, so substrate crystals can be easily obtained, and high concentration doping is possible.

It is possible to obtain a layer with low resistivity, it is easy to form an electrode contact with low ohmic resistance, it has low thermal resistance, and the heat generated near the active layer can be quickly dissipated. Things like that.

However, the band gap energy of GaAa is about 1.42 eV, and there is a large difference between the band gap energy of the crasito layer and the band gap energy of GaAa.
- In general, a potential barrier is formed at the interface between two semiconductor layers having the same conductivity type and different band gaps due to band discontinuity. The height of such a barrier is considered to be larger as the band discontinuity becomes larger, and generally, the greater the difference in band gaps, the greater the severity of the band discontinuity between the two semiconductors. Therefore, a large potential barrier is formed at the interface between the two semiconductor layers with a large band gap difference. It is also known that the thickness of the barrier O is mainly determined by the carrier concentration of a layer with a large band gap O, and that the higher the carrier concentration, the thinner the layer becomes. In order to inject a current through an interface where a barrier exists.

It is necessary to reduce the height of the barrier by applying a high 4-pressure, or to make the barrier thinner by doping at a high concentration, so that the current flow due to the tunnel effect becomes dominant.

The inventors of the present invention repeatedly conducted experiments, and found that in a conventional*eo+ conductor laser as shown in Fig. 3, which used InGaP, (r active layer, InGaAjP as the cladding layer, QaAsJj board, and middle layer), If the band gap energy of the cladding layer was 2.15 eV or less, there was no major problem in current injection, and the operating voltage was as low as about 2.0 V. However, when the band gap of InGaAjP cladding 1 was set to 2.15 eV or more, Then, the dynamic field gradually increases and the bandgap is 2.35 eV.
When GaAjP was used as the cladding layer, the operating voltage was as high as 3.5 V or more, and no material showing good characteristics was obtained.

crt is InGa, which has a large band gap with GaAs.
This is thought to be due to the fact that the above-mentioned barrier was formed at the GaAa-InGaAAtP interface because it is difficult to obtain a layer with high carrier concentration in AjP.

The present invention has been made in consideration of the above circumstances.

The objective is to find Df(
In lasers as well, the objective is to provide a semiconductor laser that achieves high reliability without increasing the operating voltage.

[Structure of the invention]

(Means for solving the problem of TIA) In the present invention, between the rad layer with a large band gap and the contact layer with a small band gap - an intermediate band gap layer and a cladding layer having an intermediate layer with a band gap between the two. The same layer provides a superlattice layer, and an intermediate bandgap layer is provided between the superlattice layer and the contact layer.

(Function) By providing the intermediate layer bandgap IiI, it is possible to reduce the influence of the barrier generated at the interface and reduce the operating voltage.

(Implementation row) The details of the present invention will be explained below with reference to illustrated embodiments.

FIG. 1 shows a meridional conductor according to a first embodiment of the present invention.
11 in Figure 0, which is a cross-sectional view showing a schematic configuration, is N-GaAs.
On this substrate 11, N-Ino,s (
Gal -xAjx)o, @Pe N-Intermediate Band Gear 9P Id 12. N-In6. (Gas-yAj,
) a, , IP eN-Clad Ill 13 , In,
, l (Gal-zAjz)6. @*P active layer 14
m P -I nO*lCG &I-y A j y
) o, sP e P - cladding layer 15 * P -
In, ), = (Gas-xAjx)0. Ip lP-intermediate bandgap layer and P-In0. , (Ga
p-yAny). as p, P-superlattice 1j 16 e P-In6. with the same structural layer as the cladding layer. * (G
as-XAjx)6. , P aP - intermediate bandgap 1il17. P-GaAs, P-electrode contact layer 1
8 are formed in sequence.

An insulating film 19 of 5lO1 or the like is formed on Cζ of the P-electrode contact layer 18, and this insulating film 19 is removed in a striped pattern. Insulating film 18. A P@electrode 20 is formed on the upper surface of the P@ electrode contactor 1118. Further, the substrate 11 has a role as an n-electrode contact layer, and an N-side electrode 21 is formed on the lower surface of the substrate 11.

In the above monument, the bandgap-thickness and carrier concentration of each layer are set as follows. N-GaA
s substrate 11 (1,42eVe70μm, 3X10"c
ar”) I N-intermediate bandgap layer 12 (2,
16V#0.2μmt3X10"cm-')e N-cladding layer 13 (2,35a Vz 1.5ttme l
Xl0"cm-') #Active layer 14 (2,0OeVt
0.5 (Ga1μms undoped), p-ri 9w de 11
i 1 5 (2.35 eV, 1.5 μm,
5X10" C "easy", P-superlattice layer 16 (respectively 2.1eV, 2.35eVti layer is 3~10λe
3 X 10"cm-1)e P-intermediate bandgap layer 17 (2,1eV, 250A*3X10"
crrr” ”) -P-GaAa'iaE pole)y tact layer 18 (1,42eve 0.2am3 X 1
0"cm").

The difference between the above structure and the conventional Ill structure is that the P-cladding layer 15 and the P-GaAs electrode contact layer 18 contain P.
- A superlattice 116 with a structure layer similar to the intermediate bandgap layer and the P-cladding layer, and the P-intermediate bandgap 1a17
This is because we have established Further, the carrier concentration of the superlattice layer 16 and the intermediate bandgap rfi 17 is larger than that of the P-cladding layer 15.

Regarding the superiority of such a structure, n It(1, p
Since it is considered to be the same with atl, here, the P-cladding layer 15. P-superlattice layer 16. P-intermediate band gear v
7' 1m 17- The column distribution of the P-electrode contact layer 18 is shown in FIG. 2, and will be described below using n as a column.

It has a large bandgap difference. P-clad layer 15
When the P-electrode contact layer is directly bonded to the P-electrode contact layer, a large barrier is formed as shown in FIG.

Furthermore, it is extremely difficult to dope P-InGaAjP, which is a P-clad layer and has a wide band gear, to a high degree of doping. It is difficult to penetrate the barrier due to the tunnel effect.

On the other hand, as shown in Fig. 2, P-clad rd15
By forming a P-superlattice layer and an intermediate bandgap layer between the P-quadrupole contact layer 18 and the P-quadrupolar contact layer 18, the height of the barrier at each interface can be reduced. Also p −'&
to the contact layer 18.

Since high doping is possible, it is possible to reduce the barrier height.

From this, according to the SC implementation plan, there is a large band gear difference between the cladding layer and the electrode contact 10.
It is possible to produce a semiconductor laser device with high reliability without increasing the operating voltage even if the laser is manipulated,
Its usefulness is enormous.

Further, the fifth factor is 511 in the cross-sectional view showing the schematic structure of the semiconductor laser according to the second embodiment of the present invention.
-GaAs substrate, and on this substrate 511 there is an n-GaAs substrate.
The As buffer layer 1512 and the n-InGaP buffer layer 513 are layered.

/(277 layer 513 top n-InGaP1l 5
14゜InGaP activity i1 activity 15 and p-InGaA
A double heterojunction structure consisting of jP cladding layers 516, 517, and 518 is formed. Here, the cladding layer 517 has a low Aj composition and also acts as an etch stop layer. Further, the cladding 1518 is processed into a striped shape, thereby forming ribs on the p cladding layer iζ stripes. On the cladding layer 518 is a superlattice layer 519 made of p-InAjP and p-InGaP. and p-InGaP intermediate band gear F layer 5
-20. and a p-GaAs contact layer 5-21. An n-GaAs current blocking layer 522 is formed on the side surface of the double hetero contact structure and the contact layer 5210. Contact layer 521 and current blocking layer 5
It sp-G a As contact on 22)li
523 is formed. And contact layer 523
A gold 14it electrode 524 is coated on the upper surface, and a 6ζ metal Tt electrode 525 is coated on the lower surface of the substrate 511.

In this structure, current confinement is performed by a contact layer 521 and a current blocking layer 522, and optical waveguide is performed by a cladding layer 51B formed in a striped mesa. In addition,
The buffer layer 513 is made of InGaA formed on GaAs.
This is to improve the quality of jP-based crystals.

The difference between the above # structure and the conventional structure is that p-clad @
51B and the GaA1:r contact layer 521, a p-
Intermediate bandgap layer (!:p-/u.

The reason is that a superlattice layer 519 and a p-intermediate bandgap layer 520 having the same structure as the de-layers are provided. Also.

The carrier concentration of the superlattice layer 519 and the intermediate bandgap layer 520 is larger than that of the cladding layer 51B.

As mentioned in the first embodiment, the advantage of this type of structure is that the large barrier formed by directly bonding the cladding 1518 and the contact layer 521, which have a large band gap difference, can be explained as follows. Clad I! 15
By forming the superlattice layer and the intermediate band gap 11 between the layer 18 and the free layer 521, the height of the barrier at each interface can be reduced. tap-contact@52
Since it is possible to dope 1 with a high concentration, the height of the buffer can be reduced.

The wafer thus obtained was separated and the resonator length was 250 mm.
When we created a μm laser device, we found that the threshold current was 40
Good characteristics with a mA differential quantum efficiency of 20% per side were obtained. The optical output increased linearly to 10 mW or more as the drive current increased, showing excellent current-light output characteristics without kinging. Also.

Both the far-sightedness 1 and the near-field image were clear, indicating that good mode control was being performed. Furthermore, the oscillation spectrum oscillation W is much wider than that of a semiconductor laser of 100 nm, so noise induced by externally reflected light is significantly reduced. Furthermore, the operating voltage is as low as 2.2V.

Note that the present invention is not limited to lasers using the materials described in the above-mentioned embodiments. For example, GaA as a substrate may be used.
using Zn5l-xsex*cu as the cladding layer.
Even in a semiconductor laser using GaAs as an electrode contact layer using Gast or the like, its usefulness is enormous. The present invention can be modified and implemented in various ways without misunderstanding the gist of the invention.

〔Effect of the invention〕

According to the present invention, it is possible to realize a semiconductor laser device having a low operating voltage and high reliability even in a semiconductor laser trap arrangement having a large band gap difference between the cladding layer and the electrode contact layer. Its usefulness is enormous.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing the schematic structure of the semiconductor laser according to the first embodiment of the present invention, Figure 92 is a characteristic diagram showing the potential distribution of the semiconductor laser shown in Figure 1, and Figure 3 is a diagram of the conventional semiconductor laser. FIG. 4 is a characteristic diagram showing the laser Q potential distribution of a conventional example, and FIG. 5 is a schematic structural diagram of a semiconductor laser according to the second embodiment. 11=n-GaAs substrate, 12- n-InG
aAjP intermediate bandgap layer, 13...n-InG
aAjP cladding layer, 14... undoped InGaA
jP/i sex layer. 15...p-InGaAjP cladding layer, 16.
p-superlattice #, 17...p-InGaAjP intermediate bandgap lii, 18...p-GaAs electrode contact layer, 19...insulating film, 20.21...electrode layer, 511...n -GaAs substrate, 512...n-
GaAs first buffer layer. 513...n-InGaP Ka2 buffer layer, 51
4...n-InAjP first cladding layer, 515-undoped InGaP active layer, 516-p-InAjP second cladding rf#, 517 = p-InGaP
Ka3 cladding layer (etching stop layer), 518...p
-InAlP fourth clad V+IJ, 519-.p-superlattice layer, 520.p-InGaP intermediate bandgap layer, 521...p-GaAs second contact r@, 52
2 ・= n-GaAst flow blocking layer, door 23...p-
GaAs third contact layer. 524.525...electrode. Figure 1 Figure 3 Figure 3 Figure d i 4

Claims (5)

[Claims] (1) a first semiconductor layer of a first conductivity type; a second semiconductor layer of a first conductive wall having a wider band gap than the first semiconductor layer;
The method includes at least a third semiconductor layer with a first conductive wall narrowed adjacent to the first and second semiconductor layers, and is operated by movement of carriers from the second semiconductor layer to the first semiconductor layer and the third semiconductor layer. 1. A semiconductor laser device, wherein the third semiconductor layer is formed of a superlattice in which a material forming the first semiconductor layer and a material forming the second semiconductor layer are laminated. (2) The semiconductor laser device according to claim 1, wherein the first conductivity type is P type. (3) The first semiconductor layer is InGaP, and the second semiconductor layer is In_
0__. _5(Ga_1_-_xAl_x)_0_. ＿５
3. The semiconductor laser device according to claim 2, wherein P has an Al composition of x=0.8 or more, and is substantially lattice matched to a GaAs substrate. (4) The first semiconductor layer is InGaP, and the second semiconductor layer is In
3. The semiconductor laser device according to claim 2, wherein the semiconductor laser device is made of AlP and is substantially lattice-matched to a GaAs substrate. (5) The semiconductor laser device according to claim 3 or 4, wherein the semiconductor element is a visible light semiconductor laser.