JP2932709B2 - Semiconductor laser - 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, high-output semiconductor laser used as a light source for information processing equipment such as an optical disk.

[0002]

2. Description of the Related Art Among practical semiconductor lasers, an AlGaInP semiconductor laser which oscillates a laser beam having the shortest wavelength has attracted attention as a light source for information processing equipment such as an optical disk. In order to write information on a magneto-optical disk or a phase-change optical disk, a high output and stable light output in the basic transverse mode and high reliability are required. In an optical disk using an AlGaAs semiconductor laser, since the semiconductor laser is driven with an optical output of 30 to 40 mW, the AlGas is used.
When an InP semiconductor laser is used, it is considered that such an optical output is required. Recently, Fujii et al.
It has been reported that a maximum of 20 mW fundamental transverse mode optical output has been obtained from a semiconductor laser (H. Fujii).
i et al. Electronics Lett;
ers, vol. 23 pp. 938-939, Aug
1987). In this semiconductor laser, the GaAs light absorbing layer covering the mesa-type AlGaInP cladding layer provides a sufficient lateral effective refractive index difference required for stable fundamental transverse mode oscillation. However, the mode loss of the semiconductor laser is large due to the GaAs light absorbing layer. This large mode loss increases the drive current of the semiconductor laser.

When a semiconductor laser is driven for a long time, it is known that a dark line defect often grows inside the semiconductor laser and the semiconductor laser is deteriorated. On the other hand, Fukaya et al. Used a semiconductor laser using an InGaAs layer having lattice strain instead of a GaAs layer lattice-matched to a semiconductor substrate, and suppressed the growth of dark line defects in the InGaAs layer. It is reported that the reliability was improved (the 51st Autumn Meeting of the Japan Society of Applied Physics, 1990, 28a-R-11).

[0004]

In order to use an AlGaInP semiconductor laser as a light source for an optical disk, it is necessary to sufficiently reduce the drive current and sufficiently increase the reliability so that the AlGaInP semiconductor laser can be driven by a small drive circuit. is there.

[0005]

SUMMARY OF THE INVENTION A semiconductor laser according to the present invention comprises a first conductivity type GaAs substrate on a first conductivity type GaAs substrate.
aInP cladding layer and first conductivity type or second conductivity type A
A high reflectivity semiconductor Bragg reflector comprising a multilayer epitaxial layer including at least an active layer of GaInP or GaInP and a mesa-type AlGaInP cladding layer of a second conductivity type, wherein the entire or part of the mesa-type cladding layer comprises a GaAs layer and a GaInP layer. It is characterized by being covered with.

Another semiconductor laser of the present invention is a semiconductor laser of the first conductivity type on a GaAs substrate of the first conductivity type.
nP cladding layer and first conductivity type or second conductivity type AlG
a high reflectivity semiconductor Bragg lifter comprising a multilayer epitaxial layer including at least an aInP or GaInP active layer and a second conductivity type mesa-type AlGaInP cladding layer, wherein the entire or part of the mesa-type cladding layer is composed of an InGaAs layer and a GaInP layer It is characterized by being covered with.

[0007]

According to the first semiconductor laser of the present invention, a GaAs layer and a Ga layer are used instead of the conventional GaAs light absorbing layer described above.
A semiconductor Bragg reflector made of an InP layer is used.
Laser light permeates into the GaAs layer and the GaInP layer. At this time, since the GaAs layer and the GaInP layer have a refractive index larger than the effective refractive index of the optical waveguide, the electric field intensity of laser light (TE mode) immersed in these layers, E
_y (x), is represented by _{E y (x) ~exp (-α} · x / 2) · exp (j · κ x · x) (1). Here, the x-axis, the z-axis, and the y-axis are the vertical direction of the substrate, the direction of the resonator, and the direction orthogonal thereto. κ _x is the wave number in the x direction, α is the absorption coefficient, and j is the imaginary unit. The wavelength in the x direction, λ _x , is represented by λ _x = 2π / κ _x (2). A semiconductor Bragg reflector composed of a GaAs layer and a GaInP layer each having a thickness close to λ _x / 4 has a high reflectivity to laser light and gives a sufficient effective refractive index difference in the lateral direction of the optical waveguide. At this time, the depth of penetration of the laser beam into the semiconductor Bragg reflector is reduced, and the mode loss is reduced.

[0008] The second semiconductor laser of the present invention is GaAs.
Layer / GaInP layer instead of InGaAs layer / GaIn
A semiconductor Bragg reflector composed of a P layer is used. In
Since the GaAs layer has a refractive index larger than the effective refractive index of the optical waveguide, similarly to the GaAs layer, the semiconductor Bragg reflector has a high reflectivity to laser light and reduces mode loss. Further, the InGaAs layer having lattice distortion suppresses the growth of dark line defects generated from the inside and the interface.

[0009]

FIG. 1 is a sectional structural view showing an embodiment of a first semiconductor laser according to the present invention. First, Si-doped n-Ga
A 1.2 μm thick Si-doped n-G
aInP clad layer 3, undoped AlG with a thickness of 60 nm
aInP active layer 1, 1.2 μm thick Zn-doped p-Al
GaInP cladding layer 2, 20 nm thick Zn-doped p-
A GaInP layer 5 was grown. In order to obtain an oscillation wavelength of 660 nm, the composition of the active layer and the cladding layer is (Al _0.1 G
a _0.9 ) _0.5 In _0.5 P and (Al _0.7 Ga _0.3 )
_0.5 In _0.5 P. The epitaxial growth was performed by a reduced-pressure metal organic crystal growth method (MOVPE method). In the growth of the active layer and the cladding layer, a growth temperature of 660 ° C.,
Using a group III flow rate ratio of 150, the growth rate at this time was 1.8.
μm / hr. The raw materials are trimethyl aluminum (TMA), triethyl gallium (TEG), trimethyl indium (TMI), dimethyl zinc (DMZ),
Phosphine (PH ₃ ), arsine (AsH ₃ ), and disilane (Si ₂ H ₆ ) were used. It is also possible to grow using a gas source molecular beam crystal growth method (GSMBE method) or a chemical beam epitaxial method (CBE method).

After the epitaxial growth, the p-GaInP layer 5 is formed by a wet etching process using the striped SiO ₂ dielectric film formed on the p-GaInP layer 5 by vapor deposition and photolithography as a mask.
And the p-AlGaInP cladding layer 2 was partially removed. Next, using the SiO ₂ dielectric film as a mask, n-G
MOV aAs / n-GaInP Bragg reflector 4
It was selectively grown by PE method. FIG. 2 is a structural diagram of the Bragg reflector. Si of the Si-doped n-GaAs layer of the Bragg reflector 4 layers (thickness L _a = 90 nm) and 3-layer
Doped n-Ga _0.5 In _0.5 P layer (thickness L _b = 140 n
m). After selective growth of the Bragg reflector,
The SiO ₂ was removed, and a Zn-doped p-GaAs layer 6 was further grown. Finally, the p-GaAs layer 6 and the n-G
After the electrodes 7 and 9 were formed on the surface of the aAs substrate 8 respectively, cleavage was performed to complete a semiconductor laser. p
-GaInP layer 5 and p-GaAs layer 6 are made of p-Al
It was introduced to reduce the electric resistance between the GaInP cladding layer 2 and the electrode 7.

In FIG. 1, a mesa-type p-AlGaInP
Cladding layer 2, undoped AlGaInP active layer 1, and n
-The AlGaInP cladding layer 3 constitutes an optical waveguide.
The refractive indices of the active layer and the cladding layer are 3.50 and 3.32. Since the active layer is sufficiently thin, the propagation vector of the laser beam in the z direction, β, is expressed as β β3.32 · k ₀ (3) using the refractive index of the cladding layer. Here, k ₀ is the wave number in a vacuum, and k ₀ = 2π / λ ₀ = 9.520 μm ⁻¹ (4) for the oscillation wavelength λ ₀ = 660 nm. The electric field strength of a laser beam having a propagation vector, β, immersed in a layer having an effective refractive index of the optical waveguide, β / k ₀ , which is larger than the refractive index, n _B , is expressed by equation (1). You. The wave number k _x in the x direction in the expression (1) is represented by k _x = (n _B ² · k ₀ ² -β ² ) ^-1/2 (5). Since the refractive indexes of the GaAs layer and the GaInP layer are 3.79 and 3.53, respectively, using equations (2) and (5), λ _x / 4 of these layers is about 90
nm and 130 nm. In this example, the thicknesses of these layers were determined based on the results.

FIG. 3 shows a calculation result of the mode loss of the semiconductor laser.

L _a / k _xa = L _b / k _xb = L _R (6) Here, L _a and L _b is the thickness of the GaAs layer and GaInP layer in the semiconductor Bragg reflector, k
_xa and k _xb is the wave number in these layers, a k _x. FIG.
As shown in FIG. 7, the mode loss is significantly reduced around L _R = １ ／.

According to a second embodiment of the semiconductor laser of the present invention, the Si-doped n-G
Si-doped n-In _0.1 Ga _0.9 A instead of the aAs layer
An s layer (90 nm thick) was used. The In _0.1 Ga _0.9 A
Although the refractive index of the s layer is slightly higher than that of the GaAs layer, λ _x / 4 is almost the same as that of the GaAs layer.
This embodiment is exactly the same as the above embodiment except that the In _0.1 Ga _0.9 As layer is used.

[0015]

The semiconductor laser of the present invention has a small mode loss and can be driven with a low driving current. In addition, the growth rate of dark line defects is low, and high reliability can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross-sectional structure of a semiconductor laser of the present invention.

FIG. 2 is a diagram showing a structure of a semiconductor laser GaAs / GaInP Bragg reflector of the present invention.

FIG. 3 is a diagram showing a mode loss reduction effect of the semiconductor laser of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Undoped AlGaInP active layer 2 p-AlGaInP clad layer 3 n-AlGaInP clad layer 4 n-GaAs / n-GaInP Bragg reflector

Claims (2)

(57) [Claims] An AlGaInP cladding layer of a first conductivity type and a first conductivity type or a second conductivity type are formed on a GaAs substrate of a first conductivity type.
A conductive AlGaInP or GaInP active layer and a second
A multi-layer epitaxial layer including at least a conductive type mesa-type AlGaInP cladding layer, wherein the whole or part of the mesa-type cladding layer is covered with a high-reflectivity semiconductor Bragg reflector composed of a GaAs layer and a GaInP layer. Semiconductor laser. 2. A first conduction type AlGaInP cladding layer, a first conduction type or second conduction type AlGaInP or GaInP active layer, and a second conduction type mesa type AlGaInP cladding layer on a first conduction type GaAs substrate. And a multi-layer epitaxial layer including at least the following, and the whole or part of the mesa-type cladding layer is covered with a high-reflectivity semiconductor Bragg reflector composed of an InGaAs layer and a GaInP layer.