JPH01202886A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To acquire stable basic transverse mode oscillation of small astigmatism by optimizing the values of various structural parameters which determine characteristics of a semiconductor laser. CONSTITUTION:A rib-type optical waveguide is provided with a refractive index waveguide structure near a resonator end, and gain waveguide structure in the other region. The side of optical waveguide is buried with a II-VI compound semiconductor layer. The refractive index waveguide region length is set at 5-500mum at the light emitting side. At the monitor side, the refractive index waveguide region length is set at not more than 500mum, the gain waveguide region length is set at 10-500mum, the refractive index waveguide region width is set at 0.5-10mum, the gain waveguide region width is set not less than 5mum, and the current injection width is set not exceeding 10mum. In this way, stable and single transverse mode oscillation can be conducted from low light-output operation to high light-output operation, return light noises are restrained by longitudinal multi-axial mode oscillation, a laser beam of small antigmatism is outputted, and current flowing in the outside of an active region is restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a semiconductor laser that oscillates in a fundamental transverse mode and is capable of high output oscillation with low noise.

[Conventional technology]

When a semiconductor laser (hereinafter referred to as LD) is used as a light source for optical information processing such as a rewritable magneto-optical disk system, not only stable fundamental transverse mode oscillation occurs, but also a portion of the emitted light includes the disk surface. It has low-noise characteristics that oscillates stably even against noise caused by interference effects when it is reflected from the external optical system and returns to the LD resonator (hereinafter referred to as "return optical noise"), and it also has low noise characteristics that allow it to oscillate stably even when writing information to the disk. Alternatively, it is necessary to have a high optical output characteristic of several tens of mW or more when erasing written information.

Therefore, as a means for realizing the above characteristics, a first cladding layer, an active layer, a waveguide layer of the first conductivity type, and a second iwi type second conductivity type are formed on the first conductivity type compound semiconductor substrate.
A rib-shaped optical waveguide is formed by removing up to the second cladding layer of a structure in which cladding layers are sequentially laminated, and the optical waveguide has a width that corresponds to the width of the optical waveguide and the current injection in the vicinity of at least one resonator end face. The width of the optical waveguide is substantially equal to form a refractive index waveguide structure, and in the area other than the refractive index waveguide structure, the width of the optical waveguide is made sufficiently wider than the current injection width to form a gain waveguide structure, and the rib-shaped The surface of the optical waveguide had a semiconductor laser embedded in a ■-■ group compound semiconductor layer.

(Problems to be Solved by the Invention) However, the above-mentioned prior art has the following problems with various parameters that influence the LD characteristics.

1) Since there is no limitation on the width of the optical waveguide near the output end face, single transverse mode oscillation cannot be obtained if the refractive index waveguide width becomes wide.

2) Therefore, not only is a complicated optical system required for each ILD application, but it is also impossible to put it to practical use.

3) When the width of the gain waveguide region becomes narrower, the refractive index waveguide component increases and longitudinal multi-axis mode oscillation becomes impossible.

4) L due to inappropriate setting of optical waveguide width, etc.
The oscillation threshold current of D increases.

5) Therefore, the amount of heat generated within the element increases and the reliability of the LD deteriorates.

Therefore, the present invention is intended to solve these problems.The purpose of the present invention is to perform stable single transverse mode oscillation from low optical output operation to high optical output operation, and to reduce the return light by vertical multi-axis mode oscillation. The object of the present invention is to provide an LD capable of low threshold oscillation, which suppresses noise, emits laser light with a small astigmatism difference, and suppresses reactive current flowing outside the active region as much as possible.

[Means to solve the problem]

The semiconductor laser of the present invention has a first Aβ-xGtL s -x of a first conductivity type on a GaAs substrate of a first conductivity type.
A S Crab layer (1≧x>0)s AJyG a
s −y As active layer (x>y), Aj2+ Ga
s+ u A s waveguide layer, and a second waveguide layer of a second conductivity type.
Aj2z Gas-! As cladding layer (z>y)
The second AIIz Oat -! has a structure in which layers are sequentially laminated.
A rib-shaped optical waveguide is grown by removing the As cladding layer up to the AρuGam-aAs waveguide layer, and the optical waveguide has a width approximately equal to the current injection width near at least one resonator end face. It has a refractive index waveguide structure,
In a region other than the refractive index waveguide structure, the width of the optical waveguide is made sufficiently wider than the current injection width to form a gain waveguide structure, and the surface of the rib-shaped optical waveguide is formed by a II-Vl group compound semiconductor layer. In a semiconductor laser embedded in a semiconductor laser, the length of the refractive index waveguide region on the light emission side is 5 to 500 μm, the length of the refractive index waveguide region on the monitor side is 500 μm or less, the length of the gain waveguide region is 10 to 500 μm, and the length of the refractive index waveguide region on the monitor side is 5 to 500 μm. Region width is 0.5 to 10 μm
1 gain waveguide region width is 5 μm or more, current injection width is 10 μm
It is characterized by the following:

〔Example〕

The present invention will be explained in detail below. Here, except for the buried layer made of ZnSe, AJ2G, which is a representative compound semiconductor, is used.
Although the aAs compound semiconductor is taken as an example, the present invention can be implemented in the same manner with other compound semiconductors and even with structures in which all the conductivity types in the description are reversed.

FIG. 1 shows the structure of an LD according to the present invention, and FIG. 2 shows a manufacturing process diagram thereof. Hereinafter, the structure etc. will be explained using FIG. 2.

n-type GaAs on the n-type GaAs substrate (201)
Buffer y-layer 202, n1l-AJ2xGat-xA
SAlO2 rad rA203, A(ly Gas-y
As active layer (x>y) 204, Aρu G &, -u
A s 83 wave layer 205, p-type -AρzG&+-zA
s second cladding ffi (z>y) 20B, p-type Ga
A structure consisting of an As contact layer 207 is continuously formed (FIG. 2(a)). The growth of each of the above layers is carried out using the liquid phase growth method (
(hereinafter referred to as LPE method), Renki metal vapor phase epitaxy method (hereinafter referred to as MO
This can be performed by a method such as a CVD method (hereinafter referred to as a CVD method) or a molecular beam growth method (hereinafter referred to as an MBE method). Next, a rib etching mask 208 is applied to the shape as shown in the shaded area 209 in FIG. 2 (C1).
form.

Subsequently, p! ! ! -G a As contact layer 207 and p! ! -AρzGam-zAs The second cladding layer 206 is removed by etching to form a rib having the same shape as the etching mask 208. Since the etching island, the second cladra layer 206, and the waveguide layer 205 have different Aρ mixed crystal ratios, a difference occurs in the etching rate. At this time, the waveguide B2O5 can also be used as an etching stop layer.

(FIG. 2(d)) Subsequently, a ZnSe buried layer 210, which is a ■-■ group compound semiconductor, is grown by MOCVD or the like. MOCVD
When this method is adopted, extremely uniform film thickness -1 can be achieved on the wafer surface on which ribs are formed. (Figure 2(e)).

Next, the ribbed ZnSe sheet is removed by etching into stripes. The top view of the element after etching is shown in the second figure.
Figure (shown in the illusion. The shaded area is the ZnSe buried layer 210, and the stripe in the center is f) Ml -G a A
This is the exposed portion of the s-contact layer 207. Thereafter, the LD is formed by forming the p-type anti-static Ti 211, performing a backside substrate removal process, and forming the n-side electrode 212.

The refractive index of the ZnSe-embedded 71210 used in the present invention is smaller than that of the A,9GaAs layer with any Aρ mixing ratio, and the forbidden band width is smaller than that of the A9GaAs layer with any Aρ mixing ratio.
It is a wider material than the aAs layer.

Therefore, the waveguide formed according to the present invention is made of ZnSe
Since the layer does not absorb the laser oscillation light, a refractive index difference formed by the real part of the complex refractive index occurs in a direction horizontal to the junction, forming a refractive index waveguide.

Therefore, in the vicinity of the resonator end face, the width of the refractive index waveguide and the current injection width are approximately the same, resulting in a refractive index waveguide a structure, which enables stable single transverse mode oscillation and an extremely small astigmatism difference. Laser light is emitted.

On the other hand, in the center of the resonator, by making the width of the refractive index waveguide sufficiently wider than the current injection width, it becomes a gain waveguide mechanism, resulting in vertical multi-axis mode oscillation, and return optical noise can be suppressed as much as possible.

Furthermore, since the ZnSe layer is a material with high resistivity (1010 cm or more), current confinement is effectively performed, and reactive current flowing outside the active region can be suppressed as much as possible.

Table 1 shows each structural parameter (a
~r: see FIG. 1) is shown.

Regarding sample numbers 1 to 6, when each parameter is within the range limited by the present invention, all samples satisfy fundamental transverse mode oscillation and longitudinal multimode oscillation, and astigmatism is also eliminated. This is an extremely small value of several μm or less. On the other hand, in sample numbers 7 to 10, some of the parameters are outside the range defined by the present invention. For such samples, changes in characteristics such as transverse mode oscillation at a higher order, threshold current becoming large, longitudinal mode oscillating in a single mode, or extremely large astigmatism may occur. arise. In such a case, when the LD is used as a light source for an optical information processing device or the like, problems arise such as the need for a complicated external optical system, making it impossible to put it to practical use. Therefore, it is optimal to set each parameter within the range limited by the present invention.

Table 1 b: Gain waveguide region length C: Monitor side refractive index waveguide region length d Double gain waveguide region width e: Refractive index waveguide region width f: Current injection width ■th Niji threshold current (effect of the invention ] As described above, according to the present invention, the following effects can be obtained by optimizing the values of various structural parameters that determine the characteristics of the LD.

! ) By optimizing the structural parameters of the refractive index waveguide region near the light exit end face, stable fundamental transverse mode oscillation with extremely small astigmatism can be obtained.

2) Due to the above reasons, it becomes possible to install it in various LD application devices without requiring a complicated external optical system.

3) By optimizing the numerical values of the structural parameters of the gain waveguide region, this LD achieves longitudinal multimode oscillation.

4) Therefore, oscillation with extremely low return optical noise can be obtained.

5) In addition, low noise is achieved without the need for additional circuitry required by the high-frequency gravimetric method used to counter optical return noise, and it also leads to a lighter optical head, allowing high-speed access. You can expect it.

6) The lip side surface is embedded with a ZnSe layer of low refractive index material, and directly above the active layer is AρGaAsj! ! Since there is a waveguide range of more than 100 nm, the degree of freedom in controlling the refractive index step that influences optical confinement in the horizontal and vertical directions at the junction increases.

7) Therefore, while maintaining the fundamental transverse mode oscillation, the spot size of the near-field image can be expanded, and high optical output oscillation becomes possible.

[Brief explanation of the drawing]

FIG. 1 (al to IcI are structural diagrams showing one embodiment of the LD of the present invention, (al is a top view, lbl and (01 are
(al is a cross-sectional view at AA'IIB' shown in FIG. 2.
01-...n-type GaAs substrate 202-n! ! -G a -A s buffer layer 2
03-...n-type-Aj2xGam-xAs first cladding layer 204-Afly Gas-yAs active layer 205-
Aflu GAS-M AsW wave circuit layer 2oe/p
m ”AI!t Ga1-!As second degree cladding layer 207...p-type-GaAs contact layer 208.20
9...Repetching mask 210...ZnSe
Buried layer 211...P-side electrode 212...N-side electrode and above

Claims (1)

[Claims] A first conductive type GaAs substrate is formed on a first conductive type GaAs substrate.
Al_xGa_1_-_xAs cladding layer (1≧x>
0), Al_yGa_1_-_yAs active layer (x>y)
, Al_uGa_1_-_uAs waveguide layer, and a second
The second Al_z has a structure in which second Al_zGa_1_-_zAs cladding layers (z>y) of conductivity type are sequentially laminated.
Ga_1_-_zAs cladding layer and Al_uGa_1
It has a rib-shaped optical waveguide formed by removing up to the uAs waveguide layer, and the optical waveguide has a refractive index waveguide with the optical waveguide width and current injection width being approximately equal to each other in the vicinity of at least one resonator end face. In the region other than the refractive index waveguide structure, the width of the optical waveguide is made sufficiently wider than the current injection width to form a gain waveguide structure, and the surface measurement of the rib-shaped optical waveguide is II-
In a semiconductor laser embedded with ZnSe, which is a group VI compound semiconductor layer, the refractive index waveguide region length on the light emission side is 5.
500μm, refractive index waveguide region length on the monitor side is 500μm
A semiconductor laser characterized by having a gain waveguide region length of 10 to 500 μm, a refractive index waveguide region width of 0.5 to 10 μm, a gain waveguide region width of 5 μm or more, and a current injection width of 10 μm or less. .