JPH08330669A - Semiconductor laser - Google Patents

Abstract

PURPOSE: To form a current non-injection structure near the end face by simple manufacturing steps by not providing at least hetero buffer layer near the end faces of a resonator sandwiching an exciting region from the direction of the resonator length. CONSTITUTION: A stripe-like exciting region elongated in the direction of a resonator length is provided in the length not arriving at the end face of the resonator, and at least one hetero buffer layer 5 having an intermediate band gap of the both of a first clad layer 4 and a cap layer having a band gap smaller than that of the layer 4 formed on the layer 4 is provided between the layer 4 and the cap layer in the exciting region. Thus, at least the one buffer layer is not provided near the end faces of the resonator sandwiching the exciting region in the direction of the resonator length, thereby reducing the current injection amount to the vicinity of the end face of the resonator. Thus, etching step is simplified since the crystal surface to be etched is flat, and there is no anxiety of introducing the deteriorating cause on the way of the steps.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly to a semiconductor laser suitable as a light source for optical disks.

[0002]

2. Description of the Related Art In order to improve the reliability of a semiconductor laser used as a light source for an optical disk, it is important to prevent the deterioration of the end face of the resonator. A method of forming a protective film on the end face is widely used as a measure for preventing end face deterioration. FIG. 4 shows a conventional typical semiconductor laser for an optical disk. Cladding layers 2 and 4 having a large band gap are formed with the active layer 3 interposed therebetween,
A rib type optical waveguide is formed in the upper clad layer 4. The current is confined in the rib waveguide by the current blocking layer 6 and injected into the active layer. There is no current constriction structure in the longitudinal direction of the resonator, and the same high-density current injection as in the inside of the resonator is also performed on the end face of the resonator. At the cavity end face, carriers recombine non-emissively via the surface level of the crystal surface, so that the temperature locally rises and the deterioration progresses faster than inside the cavity. Therefore, protective films 10 and 11 are formed on the cavity end face, and the facet crystal reacts with oxygen in the atmosphere to oxidize,
Prevents rapid deterioration.

In the prior art, a large number of semiconductor lasers called window structures in which a semiconductor layer having a wider bandgap than the active layer is provided near the end face of the resonator have been reported. Among them, Japanese Patent Application Laid-Open No. 2-130886 describes a method of forming a window structure using a semiconductor substrate having a ridge step near the cavity facet. The window structure prevents the active layer in the vicinity of the end face from being excited by the oscillated light, thereby achieving high output.

[0004]

However, these conventional techniques have the problems described below, and cannot provide sufficient effects.

The method of forming a protective film on the end face is effective in preventing rapid deterioration due to oxidation of the crystal surface of the end face, but high-density current injection is also performed near the end face to form crystal defects. Is accelerated. Therefore, long-term prevention of end face deterioration was insufficient.

The window-structured semiconductor laser generally has a problem that a fine etching process and a high-grade crystal growth process are required to form the window structure, and a high precision is required in the manufacturing process. Further, crystal defects are easily introduced during the complicated manufacturing process, and it is difficult to manufacture a crystal having a window structure or an interface region between the window structure and the excitation region with high quality. The aforementioned Japanese Patent Laid-Open No. 2-13
In the invention described in Japanese Patent No. 0886, the window structure is complicated, and (00
It is difficult to obtain a high-quality crystal in the entire region because the crystal growth is performed simultaneously on the 1) plane, the (111) plane, the inclined plane of the boundary region between the excitation portion and the window structure portion, and the crystal planes different from each other. Met. Further, in this conventional window structure semiconductor laser, in order to prevent deterioration of the window structure region and reduce the reactive current, an n-type GaAs layer is provided on the upper portion of the window structure to prevent current injection. That is, this n-type GaAs layer also serves as a current constriction, and therefore 0.6-0.9 μm.
And thick. As a result, the surface of the element becomes uneven, and the fusion with the heat sink and the heat radiation become non-uniform, which causes deterioration or deterioration of the characteristics.

An object of the present invention is to provide a highly reliable semiconductor laser which solves these problems by forming a current non-injection structure near the end face by a simple manufacturing process.

[0008]

A semiconductor laser according to the present invention has at least an active layer and first and second clad layers having a band gap larger than that of the active layer and sandwiching the active layer. A striped excitation region extending in the longitudinal direction is provided in a length that does not reach the cavity end face, and in this excitation region, the first cladding layer and the first cladding layer formed on the first cladding layer are provided. Between the clad layer and the cap layer having a band gap smaller than that of the clad layer, at least one hetero buffer layer having an intermediate band gap therebetween is provided, and the resonance region sandwiching the excitation region from the cavity length direction is provided. At least one of the
It is characterized in that the amount of current injected into the vicinity of the cavity facet is reduced by not providing the hetero-buffer layer as a layer.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to clarify the above and other objects, features and effects of the present invention, embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 (a) is a perspective view of the entire device, FIG. 1 (b) is a sectional view of the device along the resonator taken along line AA ', and FIGS. 2 (a), 2 (b) and 3 (). (a), (b) is a figure which shows a manufacturing process.

In FIG. 2A, first, on an n-type GaAs substrate 1, an n-type (Al _x Ga _1-x ) _y having a thickness of 1.5 μm is formed.
In _1-y P (x = 0.6, y = 0.5) cladding layer 2,
Ga _0.5 In _0.5 P active layer 3 having a thickness of 0.05 μm, p-type (Al _x Ga _1-x ) _y In _1-y P (x having a thickness of 1.5 μm
= 0.6, y = 0.5) Cladding layer 4 and thickness 10
nm p-type Ga _0.5 In _0.5 P heterobuffer layer 5 is sequentially grown. Next, an etching mask 12 is formed in a region other than the vicinity of the cavity end face by a normal photolithography method or the like, and using this as a mask, p-type Ga _0.5 In
_{The 0.5} P heterobuffer layer 5 is selectively etched.
For this etching, a mixed solution of HBr and H ₂ O having an extremely low etching rate for the AlGaInP layer was used.
Next, after removing the etching mask 12, the SiO ₂ film 1
3 is formed on the entire surface of the crystal, and etching is performed using a normal photolithography method to form a SiO ₂ film with a width of about 5 μm.
Stripes. Next, as shown in FIG. (B), p-type the SiO ₂ film 13 as a mask (Al _0.6
The Ga _0.4 ) _0.5 In _0.5 P layer 4 is etched to form a ridge-shaped optical waveguide. For this etching, a mixed solution of sulfuric acid, hydrogen peroxide solution and H ₂ O was used. After that, the n-type GaAs block layer 6 is crystal-grown while leaving the SiO ₂ film on the ridge. At this time, crystal growth does not occur on the SiO ₂ film, and as shown in FIG. 3A, the n-type GaAs block layer 6 is formed by embedding the ridge portion. After removing the SiO ₂ film 13, a p-type GaAs cap layer 7 is grown on the entire surface of the crystal. After the crystal growth is completed, a normal electrode forming process, an element forming process, and an end face protective film forming process are performed, and then the process shown in FIG.
The semiconductor laser of (a) is manufactured.

As shown in FIG. 1B, the semiconductor laser of the present invention has a p-type Ga _0.5 In _0.5 P heterobuffer layer 5 as shown in FIG.
Is provided only inside the resonator, and the p-type (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P cladding layer 4 and p are provided near the end face.
The type GaAs cap layer 7 is in direct contact. (Al _0.6
The band gaps of the Ga _0.4 ) _0.5 In _0.5 P cladding layer 4 and the GaAs cap layer 7 are 2.265 at room temperature, respectively.
eV and 1.42 eV. As described above, since the band gap difference between the two semiconductor layers is as large as about 0.8 eV, a large potential barrier due to band discontinuity is formed at the interface between the two semiconductor layers, and no current flows. On the other hand, in the excitation region, Ga _0.5 In having a band gap of 1.91 eV which is an intermediate size between both semiconductor layers is used.
_{The 0.5} P heterobuffer layer 5 is provided, and the hetero interface is the interface between the AlGaInP layer and the GaInP layer and GaIn.
The interface has a small band gap difference between the interface between the P layer and the GaAs layer, the potential barrier is small, and it does not hinder electric conduction.

In the semiconductor laser of the present invention, the GaInP active layer 3 in the current non-injection region near the end face is also p-type (Al
Leakage current flows from the excitation region via the _0.6 Ga _0.4 ) _0.5 In _0.5 P cladding layer 4. The magnitude of the leakage current injected in this manner is estimated to be (operating current value) × (length of non-injection region) ÷ (length of excitation region) at maximum.
This leakage current is small and the GaInP active layer 3 near the end face is
If the density of injected carriers is too low, absorption loss for oscillation light in the current non-injection region increases, and peculiar operation such as bistable operation is exhibited. Therefore, p-type (Al _x Ga _{1 -x} ) _y In is adjusted so that the injected carrier density becomes an appropriate value.
It is necessary to set the length of the end face current non-injection region according to the electrical resistance (ρ) of the _1-y P clad layer and the layer thickness. On this occasion,
The injected carrier density at the end face is 1/2 to 1/5 of the excitation region.
By setting the length such that the light absorption coefficient in the non-injection region is is about 10 to 100 cm ^-1, the length of the non-injection region is greater than this, the light absorption coefficient of 100 cm ^-1 or more Becomes a large value, resulting in bistable operation.
In the case of this embodiment, x = 0.6, ρ = 0.66 Ω · cm,
P = 6.4 × 10 ¹⁷ cm ⁻³ and the resonator length is 700 μ
Therefore, the length of the non-implanted region was 10 to 30 μm.

The present invention is not limited to the semiconductor material, the structure of the active layer or the optical waveguide, the cladding layer, etc. described in the above embodiments, and other materials may be used as long as they satisfy the features of the present invention. Of course.

For example, the active layer is II-VI such as ZnSe.
It can also be applied to a green-blue semiconductor laser made of a group compound semiconductor. In this case, n-type ZnMgSSe is formed on the GaAs substrate.
Second clad layer composed of ZnSe active layer, p-type Zn
First cladding layer made of MgSSe, second heterobuffer layer made of ZnSe, GaInP or AlGa
First heterobuffer layer of InP and p-type G
The aAs cap layer is sequentially stacked, and the first heterobuffer layer is not provided near the cavity facet. Here, the ZnSe heterobuffer layer is provided in the first GaInP or AlGaInP layer.
First hetero-buffer layer and p-type ZnMgSSe
Since the difference in the band gap from the clad layer of Zn is large, Zn having a band gap intermediate between the two is present.
This is to improve the current injection efficiency in the excitation region by interposing the Se heterobuffer layer between them.

[0016]

According to the present invention, the current non-injection structure is provided near the end face to reduce the current injection into the end face,
A highly reliable semiconductor laser can be realized. In the current non-injection structure of the present invention, the crystal surface to be etched is flat, so that the etching process is simple, and there is no fear of introducing a cause of deterioration during the process. Hetero buffer layer to be further removed is 1
Since the thickness is as thin as about 0 nm, no unevenness on the element surface like the conventional current non-injection structure of the window structure semiconductor laser is generated, and the characteristics and reliability are not adversely affected.

[Brief description of drawings]

1A and 1B are structural views of a semiconductor laser according to an embodiment of the present invention, FIG. 1A is a perspective view of the entire device, and FIG. 1B is a device cross-sectional view taken along line AA ′ of the device.

2A and 2B are views showing a part of a manufacturing process of a semiconductor laser according to an embodiment of the present invention, in which FIG. 2A is a structural view after selective etching of a GaInP heterobuffer layer, and FIG. 2B is p-AlG.
FIG. 6 is a structural diagram of an aInP clad layer after formation of a rigid waveguide.

3A and 3B are diagrams showing a semiconductor laser manufacturing process following FIG. 2B, in which FIG. 3A is a structural diagram after selective growth of an n-GaAs block layer and removal of a SiO ₂ mask, and FIG.
FIG. 6 is a structural diagram after growth of a GaAs cap layer.

4A and 4B are a structural view of a conventional semiconductor laser, FIG. 4A is a perspective view of the entire device, and FIG. 4B is a device sectional view taken along line BB ′ of the device.

[Explanation of symbols]

1 n-type GaAs substrate 2 n-type AlGaInP clad layer 3 GaInP active layer 4 p-type AlGaInP clad layer 5 p-type GaInP heterobuffer layer 6 n-type GaAs block layer 7 p-type cap layer 8, 9 electrode 10, 11 Resonator end face protection Film 12 Etching mask 13 SiO ₂ mask

Claims (4)

[Claims] 1. A striped pumping region having at least an active layer and first and second cladding layers sandwiching the active layer and having a bandgap larger than that of the active layer, the striped pumping region extending in a cavity length direction. In the excitation region, the first cladding layer and the cap layer formed on the first cladding layer and having a bandgap smaller than that of the first cladding layer are provided in a length that does not reach the end face of the resonator. Between
At least one hetero-buffer layer having a band gap intermediate between the two is provided, and the at least one hetero-buffer layer is not provided in the vicinity of the cavity end face that sandwiches the excitation region from the cavity length direction. As a result, the amount of current injected into the vicinity of the cavity facet is reduced, and the semiconductor laser is characterized. 2. The semiconductor laser according to claim 1, wherein the first cladding layer is AlGaInP, the cap layer is GaAs, and the heterobuffer layer is GaInP. 3. The first cladding layer is ZnMgSSe, the cap layer is GaAs, and the heterobuffer layer has a first heterobuffer layer made of AlGaInP or GaInP and a second heterobuffer layer made of ZnSe. 2. The semiconductor laser according to claim 1, wherein the first heterobuffer layer and the cap layer are provided in contact with each other in the vicinity of the cavity end face without the first heterobuffer layer interposed therebetween. 4. The first cladding layer has a stripe-shaped region having a larger thickness than other portions, and a part of the stripe-shaped region is formed in the excitation region. The semiconductor laser according to claim 1, 2 or 3, wherein: