JPH01217986A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To prevent overflow of electrons and holes injected into an active layer and to enable injected current to be converted efficiently, by forming two clad layers of different compound semiconductors. CONSTITUTION:On an N-type (100) InP substrate 1, there are formed an N-type clad layer 2 of InP doped with Se, an undoped InGaAsP active layer 3, a P-type clad layer 4 of InAlAs doped with Zn and an undoped InGaAs cap layer sequentially in that order. An SiO2 CVD film is then deposited and etched to provide an SiO2 stripe. Using the SiO2 stripe as a mask, the InGaAs cap layer, the P-type InAlAs clad layer 4 and the InGaAsP active layer 3 are etched off and the N-type InP clad layer 2 is removed partially by 1.5mum. Then, a semi- insulating buried layer 5 of InP doped with Fe is formed and the SiO2 mask is removed. A P-type contact layer 6 of InGaAs doped with Zn is formed and an N ohmic electrode 7 and a P ohmic electrode 8 are formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a semiconductor laser device for long wavelength optical communication using a double heterojunction structure.

(Prior Art) Generally, in an injection type semiconductor laser device using a double heterojunction structure, holes are injected into the active layer from p-type semiconductor layers sandwiching the active layer, and n-type semiconductor layers sandwiching the active layer. and holes are accumulated in the active layer using the valence band discontinuity of the active layer as a barrier. On the other hand, electrons are injected into the active layer from the n-type semiconductor layer sandwiching the active layer, and are accumulated in the active layer using the conduction band discontinuity between the active layer and the p-type semiconductor layer sandwiching the active layer as a barrier. Holes and electrons recombine in the active layer and emit light. Light is concentrated in the vicinity of the active region due to the difference in refractive index between the active region of the active layer and the crystals on the upper, lower, left, and right sides of the active region.In a semiconductor laser device with a normal structure, an n-type semiconductor layer and a p-type semiconductor sandwich the active region. Since the materials of the layers are the same, the conduction band discontinuity between the active region and the p-type semiconductor layer and the conduction band discontinuity between the active region and the n-type semiconductor layer are the same, and the conduction band discontinuity between the active region and the n-type semiconductor layer is the same. The valence band discontinuities of the layers and the valence band discontinuities of the active region and the p-type semiconductor layer were the same. Therefore, an overflow of electrons from the active region to the p-type semiconductor layer or an overflow of holes from the active region to the n-type semiconductor layer occurs, resulting in poor current confinement efficiency in the active layer. This tendency was particularly noticeable in InP semiconductor lasers in which the conduction band discontinuity between the active region and the cladding layer was small, and the active layer thickness was several hundred angstroms or less.

(Problems to be Solved by the Invention) The present invention has the above-mentioned overflow region of electrons from the active layer to the p-type semiconductor layer, which reduces the overflow of holes from the active region to the n-type semiconductor layer. The purpose of the present invention is to provide a good semiconductor laser device that can efficiently confine and concentrate holes, electrons, and light.

[Structure of the invention]

(Means for Solving the Problems) In the semiconductor laser device of the present invention, since the two cladding layers have different compositions, there is a conduction band discontinuity between the cladding layer having p-type conductivity and the active region, and the two cladding layers have different compositions. Among the layers, the valence band discontinuity between the cladding layer having n-type conductivity and the active region can be determined independently. That is, the energy barrier for electrons due to the conduction band discontinuity between the cladding layer having p-type conductivity and the active region and the energy barrier for holes due to the valence band discontinuity can be determined independently.

The conduction band discontinuity between the cladding layer with p-type conductivity of the two cladding layers and the active region is the conduction band discontinuity between the cladding layer with n-type conductivity of the two cladding layers and the active region. By making the energy barrier larger than continuous, the energy barrier between the active region and the cladding layer with p-type conductivity is lower than that between the cladding layer with n-type conductivity and the active region. It can be taken to be sufficiently large compared to the energy of electrons injected into the active region with the energy corresponding to the conduction band discontinuity with the active region.

The semiconductor substrate forming the semiconductor laser is InP, and the p-type cladding layer is InAlAs or InGaAlA.
s and the n-type cladding layer is InP, each layer can be formed with approximately lattice matching with the semiconductor of the substrate.

If formed by organometallic vapor phase epitaxy, InP, InAlA
s.

Each layer of InGaAlAs can form good crystals and form a steep and good heterojunction interface.

(Function) In the semiconductor laser device of the present invention, the energy barrier for electrons and the energy barrier for holes can be independently set large, so that electrons can be accumulated in the active layer.

Compared to the energy of electrons injected into the active region from the cladding layer with n-type conductivity, by creating a large energy barrier for electrons to enter the p-type cladding layer from the active region, it is possible to improve the flow of electrons into the active layer. can be accumulated in

If the energy barrier for holes entering the n-type cladding layer from the active region is large compared to the energy of holes injected into the active region from the cladding layer having p-type conductivity, holes will be absorbed into the active layer. can be accumulated well.

InAlAs or InAlGa as the p-type cladding layer
If As is used and InP is used as the n-type cladding layer, I
Since a crystal lattice-matched to the nP substrate can be formed, each layer of the semiconductor laser device can be formed of good crystal.

If each layer and each heterojunction interface of the semiconductor laser device is formed by metal-organic vapor phase epitaxy, the efficiency of confining electrons and holes in the active layer will be improved.

(Example) Next, embodiments of the present invention will be described in detail.

FIG. 1 is a structural sectional view of a semiconductor laser device of the present invention. The semiconductor laser device of the present invention is first of n-type (10'O)
On an InP substrate 1, a Se-doped n-type InP cladding layer (2 μs thick) 2 and an undoped InGaAsP active layer (
0.15 m thick) 3. Zn-doped P-type InAlAs cladding layer (1.5% m thick) 4. Undoped InGaA
An s cap layer (0.5% thickness) was sequentially formed by metal organic vapor phase epitaxy. After that, the resist mask was formed by using a normal trisogera-fie after forming the Sin and CVD film about 2 times so that the stripe direction was in the (011) direction.
Hydrofluoric acid (6%) ammonium decafluoride (3
0%) solution to form stripes of SiO□.Using the 0-order Sin as a mask, remove the InGaAs cap layer with a hydrogen peroxide + sulfuric acid solution, and then remove the InGaAs cladding layer by etching with hydrochloric acid. 4 was removed, and InGaAs was
Remove the P active layer 3 and add n-In with a solution of hydrochloric acid + phosphoric acid.
P cladding layer 2 is 1.5. Removed.

Thereafter, 3 layers of Fe-doped semi-insulating InP buried layers 5 were formed by metal organic vapor phase epitaxy. (here 5in2
(InP does not grow on top of the film.) Next, the Sin mask was removed using a hydrofluoric acid (6%) ammonium decafluoride (30%) solution. Thereafter, Zn-doped p
- type InGaAs contact layer (o, s, m thickness) 6 was formed. Thereafter, an n-side ohmic electrode Fi7 was formed using an Au-Ge alloy. A p-side ohmic electrode 8 was formed by Au-Zn composite.

The semiconductor laser device thus formed has a 1.554
The characteristic temperature was approximately twice that of a semiconductor laser device in which only the p-InAlAs layer was replaced with p-InP. Moreover, the maximum value of optical output was increased by approximately 1.8 times.

The present invention is not limited to the above embodiments; for example, the semiconductor substrate may be of p-type. In that case, the cladding layer on the substrate side should be a p-InAlAs layer, the cladding layer on the contact layer side should be an n-InP layer, and the conductivity type of the contact layer should be n-type6.InAlAs layer InGaA
The present invention can also be applied to material systems other than the sP/InP system.

〔Effect of the invention〕

As described above, according to the semiconductor laser device of the present invention, overflow of electrons and holes injected into the active layer can be prevented, and the injected current can be effectively converted. Hence the characteristic temperature,
The basic characteristics of a semiconductor laser, such as the maximum value of optical output, can be improved, and a semiconductor laser element suitable for high output can be provided.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the structure of a semiconductor laser device according to the present invention. 1... InP substrate 2... N-type InP cladding layer 3- InGaAsP active layer 4 - P-type InAlAs cladding layer 5... Fe-doped semi-insulating I
nP buried layer 6...p-type InGaAs contact layer 7...n-side ohmic electrode 8...p-side ohmic electrode Representative Patent attorney Noriyuki Chika Yudo Mitsuyuki Matsuyama Figure 1

Claims (3)

[Claims] (1) The active layer that contributes to light emission and laser oscillation has a wider forbidden band width than this, and is sandwiched between two upper and lower cladding layers, one having p-type conductivity and the other having n-type conductivity. A semiconductor laser device having a heavy heterojunction structure, wherein the two cladding layers are formed of different compound semiconductors. (2) The conduction band discontinuity between the cladding layer having p-type conductivity among the two cladding layers and the active region is the same as the conduction band discontinuity between the cladding layer having n-type conductivity among the two cladding layers and the active region. 2. The semiconductor laser device according to claim 1, wherein the conduction band discontinuity is larger than the conduction band discontinuity. (3) The valence band discontinuity between the cladding layer having n-type conductivity among the two cladding layers and the active region is the same as the valence band discontinuity between the cladding layer having p-type conductivity among the two cladding layers and the active region. 2. The semiconductor laser device according to claim 1, wherein the valence band discontinuity is larger than the valence band discontinuity.