JP3053955B2 - AlGaAsP semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art A semiconductor laser device using an AlGaInP crystal has an emission wavelength band on the shorter wavelength side by 100 nm or more than a semiconductor laser device using an AlGaAs crystal.
It is possible to improve the recording density of optical discs,
Since it has the property of being able to substitute for a laser, research is proceeding toward its practical use.

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

In the above-structured semiconductor laser device,
Normally, the Al composition ratio of the p-type AlGaInP cladding layer 65 is as large as 0.6 or more, so that p-type GaAs / p-type A
In the 1GaInP junction, a large spike-like heterobarrier is formed due to large discontinuity of the valence band, and the movement of carriers is hindered.

In addition, above the ridge portion 611, the p
-Type GaInP intermediate layer 66 is replaced with 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-cladding layer 65
The size of the band discontinuity at each interface of the aInP / p-type AlGaInP junction is reduced, and the heterobarrier is reduced, so that the voltage drop in this region is reduced.
In portions other than the upper portion of the ridge portion 611 of the p-type AlGaInP cladding layer 65, p-type GaAs / p-type AlG
Since it is an aInP junction, the ease of current flow is different from that above 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 constriction is performed.

[0007]

However, the above-mentioned p-type GaAs / p-type GaInP of the conventional semiconductor laser device
In the / p-type AlGaInP structure, the voltage drop at the upper part of the ridge is reduced as compared with the other junctions but is not sufficient, so that the current confinement effect is insufficient. In particular, when a high bias is applied to the semiconductor laser device due to a high-output operation or the like, current leakage in a portion other than the ridge portion is increased, so that there is a disadvantage that the characteristics and reliability of the element are deteriorated.

An object of the present invention is to solve the above-mentioned drawbacks and to provide a semiconductor laser device having a high current confinement effect.

[0009]

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

[0010]

According to the present invention, a p-type GaAs for forming a contact layer is formed by mixing the upper portion of the ridge.
Between the intermediate layer consisting of a layer and a p-type _{Al u Ga 1-u InP (} 0 ≦ u <1), p -type GaAs valence band edge energy and p-type Al _u Ga _1-u InP valence band P-type Al _x G having a valence band edge energy intermediate between the edge energies
a _1-x As is formed. Therefore, the size of the band discontinuity at the interface between these mixed crystals becomes smaller,
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. In a portion where the mixed crystal is not formed, that is, in a portion other than the ridge portion, the p-type AlGaInP clad layer is covered with a multilayer film including a GaAs layer and an AlGaAs layer which are not mixed, so that 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, a molecular beam crystal growth method (MBE method) was used as a means for crystal growth.

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

In this apparatus, an n-type GaAs buffer layer 12, an n-type AlInP cladding layer 13, a GaInP active layer 14, a p-type AlInP cladding layer 15, and a p-type GaInP intermediate layer 16 are formed on an n-type GaAs substrate 11. The layers are formed in order. The intermediate layer 16 is laminated and formed on the cladding layer 15 and then etched by photolithography together with the cladding layer 15 to form the ridge portion 1.
It is patterned by leaving 11. On 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 is made of G
It is formed by laminating a plurality of aAs layers 17a and AlAs layers 17b. The multilayer film 17 is formed so that tunneling does not occur between the contact layer 18 and the cladding layer 15 and that the p-type AlGaAs layer 1 is formed by mixed crystal formation described later.
12 so that the Al composition ratio is 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, and the AlAs layer 17b is 100
Angstrom, and these are alternately laminated by 10 layers.

Each of the above-mentioned layers laminated on the n-type GaAs substrate 11 has a composition set so as to be lattice-matched to 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.
Of the GaInP intermediate layer 16 on the side of the multilayer film 17 and the multilayer film 17 and the p-type G
The aAs contact layer 18 is selectively crystallized by Zn diffusion to be mixed crystal, and this portion (hereinafter referred to as a diffusion region) 112 becomes a p-type AlGaAs layer. This allows
P-type GaAs / p-type Al
A GaAs / p-type GaInP / p-type AlGaInP junction is formed. In the present embodiment, Al in the intermediate layer
The composition ratio is about 0.25 calculated from the ratio of each layer thickness of the multilayer film 17.

After the 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, respectively.
A semiconductor laser device is formed.

The above p-type AlG formed by mixed crystal formation
The Al composition ratio of the aAs layer is set to be smaller than 0.6 for the following reason.

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.
1 is a graph showing a relationship with a composition ratio. In the formula representing the crystal, x and u each represent an Al composition ratio. The vertical axis of the graph indicates 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 of Al _x Ga _1-x As
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
than _u Ga _1-u InP of the valence band edge energy closer to the GaAs of the valence band edge energy.

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 caused by GaAs / GaIn.
GaAs / AlGaAs bonding surface 4 from P bonding surface 41
2 becomes smaller and the current flows more easily. 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, the A
As _{l u Ga 1-u InP,} Al composition ratios are used crystals, i.e. the GaInP 0. 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 becomes Al _x Ga _1-x
As is always closer to GaAs than to GaInP. Therefore, AlGaAs formed by mixed crystal formation
It is preferable to form the multilayer structure 17 to have a thickness such that the Al composition ratio of the layer is smaller than 0.6. Such Al
The GaAs layer is a p-type GaAs forming the contact layer 18.
By intervening between s and p-type GaInAs 16 forming the intermediate layer, band discontinuity between valence band edge energies is reduced. As a result, as shown by the solid line in the graph of FIG. 5, the current-voltage characteristic at 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, regions other than the diffusion region 112 are covered with the non-mixed multi-layer film 17, so that current flow is hindered and current leakage is reduced.

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

This device has a structure similar to that of the first embodiment.
-Type GaAs buffer layer 22, n-type AlInP cladding layer 23, GaInP active layer 24, p-type AlInP cladding layer 25, and p-type GaInP intermediate layer 26 are formed in this order, ridge portion 211 is formed by etching, and , A multilayer film 27 and a p-type GaAs contact layer 28 are respectively formed in a laminated manner. Also in the second embodiment, the above-described layers laminated on the substrate 21
The composition is set so as to match the lattice.

After the Zn diffusion, an electrode 210 made of Au—Zn is provided 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 substrate 21 side, and a semiconductor laser device is formed.

The multilayer film 27 of the second embodiment is also formed of GaAs.
It is formed by stacking a layer 27a and an AlAs layer 27b. In the present embodiment, as shown in FIG. 2, eight GaAs layers 27a and eight AlAs layers 27b are alternately stacked so that the thickness of the GaAs layer 27a and the thickness of the AlAs layer 27b are different for each layer. . The thickness of each layer is such that the lowermost GaAs layer 27a has a thickness of 160 Å and AlAs
The layer 27b is 240 angstroms, and upwardly, the GaAs layer 27a is thicker by 20 angstroms for each layer, while the AlAs layer 27B is thinner by 20 angstroms, and the uppermost layer is GaAs.
The s layer 27a has a thickness of 360 Å and the AlAs layer 27
b is formed to 40 angstroms. And FIG.
In the middle, the diffusion region 212 surrounded by the broken line is mixed with Zn to form AlGaAs as in the first embodiment.
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) to the p-type GaAs contact layer 28 side (higher side). .

In the second embodiment, the A
Since the Al composition of the lGaAs layer is formed so as to decrease gradually from 0.6 to 0 as described above, the AlGaAs
Valence band edge energy gradually approaches that of GaAs. With this configuration, as shown in FIG. 4C, the band discontinuity of the joining surfaces 44 and 45 is caused by the joining surfaces 42 and 45 of the first embodiment.
43, the potential barrier almost disappears, and the current-voltage characteristics at this portion are further improved.
This is more preferable because the current can flow more easily.

In the first and second embodiments, the intermediate layers 16 and 26 are formed 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 constituting the intermediate layer be smaller than that of the cladding layer made 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, after the first crystal growth step is completed to form a ridge portion, and until the second crystal growth is performed. Then, a protective layer is formed on the ridge above the current constriction. As this protective layer, a thin film of GaInP or GaAs, for example, 50
What is necessary is just to form about angstrom.

In the first and second embodiments, the cladding layers 15 and 25 are formed of p-type AlInP, but may be formed of p-type AlGaInP. Also, the present invention can be applied to a case where the multilayer film is composed of a GaAs layer and an AlGaAs layer.

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

In these examples, the mixed crystal was formed by Zn diffusion, but an acceptor other than Zn can be used.

In each of the above embodiments, the active layer is made of normal Ga.
A semiconductor laser device made of InP bulk crystal has been described.
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 formed of an AlGaInP mixed crystal.

[0034]

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

The AlGaInP semiconductor laser device of the present invention can be manufactured without any special device and by two crystal growths.

[Brief description of the drawings]

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

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

FIG. 3 is a graph showing a relationship between an Al composition ratio of an AlGaAs crystal and an AlGaInP crystal and a valence band edge energy.

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

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

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

[Explanation of symbols]

 Reference Signs List 11 n-type GaAs substrate 13 n-type AlInP cladding layer 14 GaInP active layer 15 p-type AlInP cladding 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 cladding layer 24 GaInP active layer 25 p-type AlInP cladding layer 26 p-type GaInP intermediate layer 27 multilayer film 28 p-type GaAs contact layer 211 ridge portion 212 diffusion region

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Atsushi Tsunoda 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Kentaro Tani 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp shares In-company (56) References JP-A-4-85981 (JP, A) JP-A-61-258487 (JP, A) JP-A-3-101285 (JP, A) JP-A-63-51685 (JP, A) JP-A-2-106082 (JP, A) JP-A-1-244690 (JP, A) JP-A-63-32983 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 JICST file (JOIS)

Claims (3)

(57) [Claims] To 1. A n-type GaAs substrate, an n-type Al _s Ga _1-s
Clt layer made of InP (0 <s ≦ 1), Al _t Ga
_An active layer made of _1-t InP (0 ≦ t <1), a clad layer made of p-type Al _s Ga _{1 -s} InP having a stripe-shaped ridge, and a p-type Al provided on the ridge. _An intermediate layer made of uGa _1-u InP (0 ≦ u <1) is laminated in this order, and is covered on the p-type Al _s Ga _1-s InP clad layer while covering the intermediate layer. A multi-layered film composed of a GaAs layer and an Al _m Ga _1- mAs (0 <m ≦ 1) layer, and a p-type GaAs contact layer are formed in this order, and the upper portion of the ridge is made of a mixed crystal. Laser device. 2. A are formed by mixed crystals the upper portion of the ridge portion of the multilayer film p-type _{Al x Ga 1-x As (} 0 <x <
1) The GaAs layer and the Al _m Ga _1- mAs 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. 2. The semiconductor laser device according to claim 1, wherein the thickness of the semiconductor laser is set. Wherein the intermediate layer is, the p-type Al _s Ga _1-s In
P-type Al _u having a smaller Al composition ratio than the P clad layer
3. The semiconductor laser device according to claim 1, comprising Ga _1-u InP.