JPH05283797A - Algaasp semiconductor laser device - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser device which is small in leakage current excluding a ridge and high in current constricting effect even if a high bias is applied when it outputs laser beams of high power. CONSTITUTION:An upper part 112 of a ridge 111 is formed of mixed crystal, whereby a P-type AlxGa1-xAs layer possessed of valence band end energy intermediate in size between P-type GaAs and P-type AlUGa1-UInP is formed between a P-type GaAs contact layer 18 and a P-type AElUGa1-UInP intermediate layer 16. Therefore, band discontinuity becomes small in size at an interface between these mixed crystal layers, so that a current flows easily from the contact layer 18 to the P-type AlGa1-xAs layer 112 and the intermediate layer 16 and concentrates on the ridge 111.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refractive index guided short wavelength band AlGaInP semiconductor laser device having a current constriction effect.

[0002]

2. Description of the Related Art A semiconductor laser device using an AlGaInP crystal has an emission wavelength band on the short wavelength side of 100 nm or more as compared with a semiconductor laser device using an AlGaAs crystal.
For improving the recording density of optical discs, He-Ne
Since it has the property that it can be used as a substitute for a laser, research is proceeding toward practical application.

In order to manufacture a practical semiconductor laser device, it is necessary to form a lateral confinement structure of light emitted from the active layer, that is, an optical waveguide structure.

FIG. 6 is a vertical sectional view showing an example of a conventional AlGaInP semiconductor laser device. This device
On the n-type GaAs substrate 61, an n-type GaAs buffer layer 62, an n-type AlGaInP clad layer 63, and AlGaI.
nP active layer 64, p-type AlGaInP clad layer 65,
A p-type GaInP intermediate layer 66 is sequentially stacked.
The intermediate layer 66 is formed on the clad layer 65 and is then etched together with the clad layer 65 to etch the ridge portion 6.
It is patterned by leaving 11. On such a state, a regrown p-type GaAs contact layer 68 is formed.
Are formed, and electrodes 610 and 69 are formed on the upper surface and on the lower surface of the substrate 61, respectively.

In the semiconductor laser device having the above structure,
Usually, the Al composition ratio of the p-type AlGaInP clad layer 65 is as large as 0.6 or more, so that the p-type GaAs / p-type A
In the lGaInP junction, a large discontinuity in the valence band causes a large spike-like heterobarrier to be formed, which hinders carrier movement.

At the upper portion of the ridge portion 611, the p
The GaInP intermediate layer 66 is replaced with the p-type GaAs contact layer 6
8 is sandwiched. Therefore, the p-type GaAs contact layer 68, the p-type GaInP intermediate layer 66, and the p-type AlGaIn
P-type GaAs / p-type G formed with P clad layer 65
The magnitude of the band discontinuity at each interface of the aInP / p-type AlGaInP junction is reduced, which reduces the heterobarrier and thus the voltage drop in this region.
Except for the upper portion of the ridge portion 611 of the p-type AlGaInP cladding layer 65, p-type GaAs / p-type AlG is used.
Since it is an aInP junction, the easiness of current flow differs from that of the upper portion of the ridge portion 611. Therefore, the electrodes 69, 61
When a bias is applied to 0, the current concentrates on the ridge portion 611. Thereby, current confinement is performed.

[0007]

However, the p-type GaAs / p-type GaInP of the conventional semiconductor laser device is used.
In the / p-type AlGaInP structure, the voltage drop at the upper portion of the ridge portion is reduced but not sufficient as compared with the other junction portions, so the current constriction effect is insufficient. In particular, when a high bias is applied to the semiconductor laser device due to operation at high output and the like, current leakage in a portion other than the ridge portion becomes large, resulting in poor device characteristics and reliability.

The present invention is intended to solve the above-mentioned drawbacks, and an object thereof is to provide a semiconductor laser device having a high current constriction effect.

[0009]

A semiconductor laser device according to the present invention comprises an n-type Al _s Ga _{1 -s} InP on an n-type GaAs substrate.
(0 <s ≦ 1) clad layer, Al _t Ga _{1 -t} In
P (0 ≦ t <1) active layer, p-type Al _s Ga _{1 -s} InP clad layer having a stripe-shaped ridge portion, and p-type Al _u G provided on the ridge portion
An intermediate layer made of a _1-u InP (0 ≦ u <1) is laminated in this order, and the intermediate layer is covered on the p-type Al _s Ga _1-s InP clad layer, Furthermore G
A multilayer film including an aAs layer and an Al _m Ga _1-m As (0 <m ≦ 1) layer and a p-type GaAs contact layer are formed in this order, and the upper portion of the ridge portion is mixed crystallized. As a result, the above object is achieved.

[0010]

According to the present invention, p-type GaAs for forming a contact layer by mixing the upper portion of the ridge with mixed crystal.
The valence band edge energy of p-type GaAs and the valence band of p-type Al _u Ga _1-u InP between the layer and the intermediate layer made of p-type Al _u Ga _1-u InP (0 ≦ u <1). P-type Al _x G having a valence band edge energy of an intermediate magnitude of edge energy
a _1-x As is formed. Therefore, the size of band discontinuity at the interface between these mixed crystals becomes small,
A current easily flows from the contact layer to the p-type Al _x Ga _{1 -x} As layer and the intermediate layer, and concentrates on the ridge portion. Since the p-type AlGaInP cladding layer is covered with the multilayer film including the non-mixed GaAs layer and the AlGaAs layer in the non-mixed portion, that is, the portion other than the ridge portion, no current flows in this portion.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. In the following examples, the molecular beam crystal growth method (MBE method) was used as the crystal growth means.

FIG. 1 is a vertical sectional view showing a first embodiment of the present invention.

In this device, an n-type GaAs buffer layer 12, an n-type AlInP clad layer 13, a GaInP active layer 14, a p-type AlInP clad layer 15 and a p-type GaInP intermediate layer 16 are provided on an n-type GaAs substrate 11. The layers are formed in order. The intermediate layer 16 is laminated on the clad layer 15 and then etched by photolithography together with the clad layer 15 to form the ridge portion 1.
It is patterned by leaving 11. On top of this state, the multilayer film 17 and the p-type GaAs contact layer 18
Are laminated.

As shown in FIG. 1, the multilayer film 17 has a G
It is formed by stacking a plurality of aAs layers 17a and AlAs layers 17b. The multilayer film 17 is a p-type AlGaAs layer 1 formed by mixed crystallization described below so that tunneling does not occur between the contact layer 18 and the cladding layer 15.
The Al composition ratio in 12 is formed to be smaller than 0.6. That is, the GaAs layer 17
a and the thickness of the AlAs layer 17b are the same as those of the GaAs layer 17a.
Is 300 Å, AlAs layer 17b is 100
The thickness is angstrom, and these layers are alternately laminated by 10 layers.

The composition of each of the layers formed on the n-type GaAs substrate 11 is set so as to be lattice-matched with the n-type GaAs substrate.

After laminating the multilayer film 17 and the contact layer 18, a portion 112 surrounded by a broken line in FIG.
Part of the GaInP intermediate layer 16 on the side of the multilayer film 17, the multilayer film 17 above the ridge portion 111 and the p-type G
The aAs contact layer 18 is mixed with Zn by selective Zn diffusion, and this portion (hereinafter referred to as a diffusion region) 112 becomes a p-type AlGaAs layer. This allows
In the upper portion of the ridge portion 111, p-type GaAs / p-type Al
A GaAs / p-type GaInP / p-type AlGaInP junction is formed. In this embodiment, Al in the intermediate layer
The composition ratio is about 0.25 calculated from the ratio of the layer thicknesses of the multilayer film 17.

After Zn diffusion, the contact layer 1 is formed by vapor deposition.
An electrode 110 made of Au—Zn is formed on the 8 side, and an electrode 19 made of Ge—Ni is formed on the substrate 11 side.
A semiconductor laser device is formed.

The above p-type AlG formed by mixed crystallization
The reason for setting the Al composition ratio of the aAs layer to be smaller than 0.6 is as follows.

FIG. 3 shows the energy of the valence band edge of GaAs and the A of Al _x Ga _1-x As and Al _u Ga _1-u InP.
2 is a graph showing the relationship with the 1 composition ratio. In the formula representing a crystal, x and u each represent an Al composition ratio. The vertical axis of the graph represents the difference in valence edge energy between GaAs and each mixed crystal. As shown in this graph, the valence band edge energies of Al _x Ga _1-x As and Al _u Ga _1-u InP depend on the Al composition ratio in the mixed crystal. Al _x Ga _1-x As Al
When the composition ratio is smaller than the Al composition ratio of Al _u Ga _1-u InP, the valence band edge energy of Al _x Ga _1-x As is Al.
It approaches the valence band edge energy of GaAs from the valence band edge energy of _u Ga _{1 -u} InP.

As a result, as shown in FIGS. 4A and 4B, the discontinuity of the valence band edge energy at the junction surface with p-type GaAs is GaAs / GaIn.
GaAs / AlGaAs bonding surface 4 from P bonding surface 41
2 becomes smaller, and the current easily flows. Therefore, the Al composition ratio of Al _x Ga _1-x As is Al _u Ga _1-u In
It is preferably smaller than the Al composition ratio of P.

In the first embodiment, A for forming the intermediate layer 16
As l _u Ga _{1 -u} InP, a crystal having an Al composition ratio of 0, that is, GaInP is used. As can be seen from the graph of FIG. 3, when the Al composition ratio in Al _x Ga _1-x As is smaller than 0.6, the valence band edge energy is Al _x Ga _1-x.
As is always closer to GaAs than GaInP. Therefore, AlGaAs formed by mixed crystallization
It is preferable to form the multilayer structure 17 in such a thickness that the Al composition ratio of the layer becomes smaller than 0.6. Such Al
The GaAs layer is the p-type GaA forming the contact layer 18.
By interposing between s and p-type GaInAs16 forming the intermediate layer, band discontinuity is relaxed during valence band edge energy. As a result, as indicated by the solid line in the graph of FIG. 5, the current-voltage characteristic in this portion is improved so that the current can flow more easily than the conventional example shown by the broken line in FIG.

On the other hand, the regions other than the diffusion region 112 are covered with the non-mixed multi-layered film 17, which hinders the current flow and reduces the current leakage.

FIG. 2 is a vertical sectional view showing a second embodiment of the present invention.

This device, like the first embodiment, has n
-Type GaAs buffer layer 22, n-type AlInP clad layer 23, GaInP active layer 24, p-type AlInP clad layer 25 and p-type GaInP intermediate layer 26 are stacked in this order, and the ridge portion 211 is etched and formed thereon. A multilayer film 27 and a p-type GaAs contact layer 28 are laminated and formed. Also in the second embodiment, the layers formed on the substrate 21 are the same as those of the substrate 21.
The composition is set so as to be lattice-matched with.

After Zn diffusion, an electrode 210 made of Au--Zn is formed on the contact layer 28 side in the same manner as in the first embodiment.
An electrode 29 made of Ge-Ni is formed on the side of the substrate 21 to form a semiconductor laser device.

The multilayer film 27 of the second embodiment is also made of GaAs.
The layer 27a and the AlAs layer 27b are laminated. In this embodiment, as shown in FIG. 2, the GaAs layers 27a and the AlAs layers 27b are alternately laminated by eight layers so that the GaAs layers 27a and the AlAs layers 27b have different thicknesses. .. The thickness of each layer is as follows: GaAs layer 27a is 160 angstroms, AlAs
The layer 27b has a thickness of 240 angstroms, and the GaAs layer 27a is thicker by 20 angstroms in each layer toward the upper side, while the AlAs layer 27B is thinner by 20 angstroms at the uppermost side.
The s layer 27a is 360 Å, and the AlAs layer 27 is
b is formed to 40 Å. And FIG.
AlGaAs formed by mixing the diffusion region 212 surrounded by a broken line with Zn in the same manner as in the first embodiment by Zn diffusion.
The Al composition of the layer is formed so as to gradually decrease from 0.6 to 0 from the p-type AlInP cladding layer 25 side (lower side) toward the p-type GaAs contact layer 28 side (upper side). ..

In the second embodiment, A of the diffusion region 212 is used.
Since the Al composition of the lGaAs layer is formed so as to be gradually decreased to 0.6 to 0 as described above,
Valence band edge energy of gradually approaches GaAs. With this structure, as shown in FIG. 4C, the band discontinuity of the joint surfaces 44 and 45 is caused by the joint surface 42 of the first embodiment.
43 is further relaxed, the potential barrier almost disappears, and the current-voltage characteristic in this part is further improved,
It is more preferable because the current can flow more easily.

In the above-mentioned first and second embodiments, the intermediate layers 16 and 26 are made of p-type GaInP.
The intermediate layer may be formed of p-type AlGaInP. In this case, it is preferable that the Al composition ratio of the p-type AlGaInP forming the intermediate layer is smaller than that of the c-type cladding layer formed of the p-type mixed crystal to be joined, in view of the valence band edge energy.

When p-type AlGaInP is used for the intermediate layer, since AlGaInP is more easily oxidized than GaInP, the first crystal growth step is completed, the ridge portion is formed, and then the second crystal growth is performed. A protective layer is formed on the ridge which becomes the current constriction portion. As the protective layer, a GaInP or GaAs thin film, for example, 50
It may be formed to have a thickness of about angstrom.

Although the cladding layers 15 and 25 are made of p-type AlInP in the first and second embodiments, they may be made of p-type AlGaInP. Further, the present invention can be applied even when the multilayer film is composed of a GaAs layer and an AlGaAs layer.

The present invention can be applied to the case where a metal organic thermal decomposition method (MO-CVD method) or the like is used as the crystal growth method in addition to the MBE method.

Further, in these examples, the mixed crystal was formed by Zn diffusion, but it is also possible to use an acceptor other than Zn.

In each of the above embodiments, the active layer has a normal Ga content.
A semiconductor laser device made of InP bulk crystal is shown.
The present invention can be applied to a double hetero structure including a quantum well active layer or a case where the active layer is composed of an AlGaInP mixed crystal.

[0034]

According to the present invention, current leakage can be prevented, current confinement can be reliably performed, the threshold value is low, and AlGaI having high reliability even when performing high output operation.
An nP semiconductor laser device can be provided.

The AlGaInP semiconductor laser device of the present invention can be manufactured by performing crystal growth twice without any special device.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a second embodiment of the present invention.

FIG. 3 is a graph showing a relationship between Al composition ratios of AlGaAs crystals and AlGaInP crystals and valence band edge energy.

FIG. 4 is a diagram showing an energy band structure of a mixed crystal heterojunction portion forming a ridge portion.

FIG. 5 is a graph showing current-voltage characteristics in the ridge portion and other portions of the semiconductor laser device.

FIG. 6 is a vertical sectional view of a conventional semiconductor laser device.

[Explanation of symbols]

 11 n-type GaAs substrate 13 n-type AlInP clad layer 14 GaInP active layer 15 p-type AlInP clad layer 16 p-type GaInP intermediate layer 17 multilayer film 18 p-type GaAs contact layer 111 ridge portion 112 diffusion region 21 n-type GaAs substrate 23 n-type AlInP clad layer 24 GaInP active layer 25 p-type AlInP clad layer 26 p-type GaInP intermediate layer 27 multilayer film 28 p-type GaAs contact layer 211 ridge portion 212 diffusion region

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Tsunoda 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Kentaro Tani 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside the company

Claims (3)

[Claims] 1. An n-type Al _s Ga _1-s on an n-type GaAs substrate.
InP (0 <s ≦ 1) clad layer, Al _t Ga
_An active layer made of _1-t InP (0 ≦ t <1), a p-type Al _s Ga _1-s InP clad layer having a stripe-shaped ridge portion, and a p-type Al provided on the ridge portion. _An intermediate layer made of _u Ga _1-u InP (0 ≦ u <1) is laminated in this order, and the intermediate layer is covered on the p-type Al _s Ga _1-s InP clad layer. , A p-type GaAs contact layer and a multi-layered film including a GaAs layer and an Al _m Ga _1-m As (0 <m ≦ 1) layer are formed in this order, and the upper portion of the ridge portion is a mixed crystal semiconductor. Laser device. 2. A p-type Al _x Ga _1-x As (0 <x <is formed by mixing and crystallizing an upper portion of the ridge portion of the multilayer film.
1) The GaAs layer and the Al _m Ga _1-m As layer of the multilayer film so that the Al composition ratio x of the layer gradually decreases in the range of 0.6 to 0 from the substrate side to the contact layer side. The semiconductor laser device according to claim 1, wherein the thickness of the semiconductor laser device is set. 3. The p-type Al _s Ga _{1 -s} In is used as the intermediate layer.
P-type Al _u having a smaller Al composition ratio than the P clad layer
The semiconductor laser device according to claim 1, which is made of Ga _{1 -u} InP.