JPH08222796A - Semiconductor laser element - Google Patents

Abstract

PURPOSE: To form a laser light spectrum of multimode, and reduce optical noise generation, by making a section parallel to the main surface of a third clad layer a parallelogram which is surrounded by a cleavage plane and a line oblique to the normal of the cleavage plane. CONSTITUTION: A first clad layer 3 composed of an N-type Alx Ga1-x As, an active layer 4 composed of Aly Ga1-y As, and a second clad layer 5 composed of P-type Alx Ga1-x As are laminated in order on a main surface vertical to the cleavage plane of an N-type GaAs substrate 1, where 1>x>y>0. An N-type GaAs current blocking layer 8 which is divided into two parts, and a third clad layer 9 which is closely sandwiched between the divided current blocking layers 8 and composed of P-type Alx Ga1-x As are formed on the second clad layer 5. The section parallel to the main surface of the third clad layer 9 forms a parallelogram which is surrounded by the cleavage plane and a line obliquely to the normal of the cleavage plane. Thereby the noise of an oscillation laser which is caused by a return light can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor laser device having an active layer made of Al _y Ga _1-y As and emitting near infrared light.

[0002]

2. Description of the Related Art Generally, a semiconductor laser device needs to focus light on a minute spot of about 1 μm which is a diffraction limit, such as a compact disc (CD) or a video disc (V).
In order to be applicable to D) etc., the following points are important.
First, in order to minimize light loss and wasteful recombination, it is necessary to have a structure for confining light energy and injection current in a specific region. Further, it is necessary to control the transverse mode for confining light in the parallel direction in the active layer of the semiconductor laser.

As an example of a structure that can satisfy these conditions,
Laser element of SAS structure (Self-Aligned Structure)
I have a child. FIG. 5 is a conventional semiconductor laser device having a SAS structure.
Where (a) is a plan view and (b) is seen from the cleavage plane direction.
FIG. n-type AlGa on the n-type GaAs semiconductor substrate 1
Buffer layer 2 made of As, n-type Al_x Ga_{1 -x} Consists of As
First cladding layer 3, Al_y Ga_1-y As active layer 4, p-type Al_x
 Ga_1-x The second cladding layer 5 made of As, made of p-type GaAs
The cap layer 6 is sequentially laminated. On top of that, n type
Made of GaAs, perpendicular to the cleavage plane and separated by a small distance 2
Split current blocking layer 8 and the two current blocking
P-type Al sandwiched between layers 8 _x Ga_1-x 3rd Ku consisting of As
A rud layer 9 is laminated. This narrow area is a strike
S1 and the total drive current flows through stripe S1.
In addition, p-type Al on the entire element surface_x Ga_1-x Third consisting of As
Cladding layer 9, then contact made of p-type GaAs
Layers 10 are stacked. Then, the n-side electrode 11 is
The p-side electrode 12 is formed on the contact layer 10 on the rear surface.
Have been. Build a device with the same structure but with the conductivity type reversed.
Both are possible.

When such a semiconductor laser device is applied to a compact disc or a video disc, a pickup optical system is constructed. In the pickup optical system, the light beam emitted from the semiconductor laser element as a point light source is condensed by the lens on the pit surface of the disk, reflected and travels backward in the optical path. The part returns to the semiconductor laser device.

It is known that this return light changes the optical density in the resonator of the semiconductor laser element, changes the optimum longitudinal mode, and causes noise in which the intensity of the laser light fluctuates irregularly. Such return light noise erroneously transmits the pit length of the disc, leading to an error in reading digital information. It is known that there are some semiconductor laser devices that generate such a large number of longitudinal mode lights that are oscillated at the same time (referred to as multimode oscillation) determined by the cavity length (the optical distance between the two cleavage planes) and have such low return light noise. ing. It is also known that return light noise correlates with the coherence of laser light.

The coherence measurement is easier than the return light noise measurement and is used as a method for selecting semiconductor laser devices. In this measurement, laser light was introduced perpendicularly to two parallel mirrors, one of which was semi-transparent, and the output light intensity emitted from the latter half of the transparent mirror that reciprocated between the two mirrors and interfered with each other was measured. , The output light intensity with respect to the mirror interval is obtained. The ratio of the maximum output light intensity peak to the output light intensity of the next peak with respect to the strongest mode light of the laser light is defined as coherence (unit:%) by changing the mirror interval.

It is said that the returned light noise, which has no practical problem, corresponds to coherence of 95% or less.

[0008]

However, for example, in the above SAS structure, in order to change the characteristics of the optical resonator, the thickness of the active layer, the impurity concentration of the first and second cladding layers, and the current blocking layer are used. Coherence is 9 even if the interval is changed.
It was difficult to always keep it below 5%. Further, it does not disclose a semiconductor laser device structure capable of reliably achieving low return light noise.

In view of the above points, an object of the present invention is to provide a semiconductor laser device which realizes a multimode laser light spectrum and produces little return light noise when used in a pickup optical system of an optical information recording / reproducing apparatus. To provide.

[0010]

[Means for Solving the Problems]
Therefore, in the present invention, the cleavage plane of the GaAs substrate of the first conductivity type is
On one main surface perpendicular to, parallel to this main surface, of the first conductivity type.
Al_xGa_1-xFirst clad layer made of As, Al_y Ga_1-y As
Active layer made of (1> x> y> 0), opposite to the first conductivity type
Second conductivity type Al, which is the conductivity type of_xGa_1-xSecond consisting of As
The clad layer and the clad layer are laminated in this order, and the second clad layer is divided into two layers.
A first conductivity type GaAs current blocking layer and
The second conductor closely sandwiched between these two current blocking layers
Electric type Al _xGa_1-xA third cladding layer of As is provided
The semiconductor laser device, the third cladding layer
The cross section parallel to the principal plane of the cleaved surface and the normal to the cleaved surface
It shall be a parallelogram surrounded by diagonal lines.

[0011]

The function of the present invention is not clearly understood, but it can be estimated as follows. In the semiconductor laser device having the oblique (OFF) stripes on the cleavage plane of the present invention, the cross section parallel to the main surface of the optical resonator is an elongated parallelogram, and therefore the laser oscillation is involved as the OFF angle increases. The ratio of the standing wave whose reflection surface is only between the cleavage planes is decreased, and the ratio of the standing wave totally reflected on the side surface of the resonator is increased.
In the latter standing wave, the wavelength can take a continuous value depending on the reflection position on the cleavage plane. for that reason,
When the OFF angle increases and the latter standing wave becomes dominant, the laser light spectrum mode becomes multimode, and the full width at half maximum of the oscillating arbitrary wavelength spectrum is widened, and the coherence decreases. .

In this way, in the semiconductor laser device of the present invention, the coherence of the laser light is lowered, and the noise of the oscillated laser light due to the returning light can be reduced.

[0013]

【Example】

Example 1 Next, an example of the present invention will be described with reference to the drawings along with a manufacturing process. FIG. 1 is a plan view of a semiconductor laser device according to the present invention. The stripe S is located between the current blocking layer boundaries 81, and its appearance will be clarified in the following description. Figure 2
FIG. 4A is a schematic view of a wafer after the main manufacturing process of a semiconductor laser device according to the present invention, where (a) is a cross-sectional view after forming a silicon dioxide layer mask, (b) is a cross-sectional view after growing a current blocking layer, and (c).
It is sectional drawing after an electrode formation.

The manufacturing process of the sectional view of the semiconductor laser device of one embodiment of the present invention is the same as the conventional method. First, n-type
A buffer layer 2 made of n-type AlGaAs having a thickness of 0.2 μm on a GaAs semiconductor substrate 1, an n-type Al _x Ga _1-x A having a thickness of 1.5 μm.
The first cladding layer 3 composed of s (carrier concentration 2 × 10 ¹⁸ cm
^-3 ), Al _y Ga _1-y As (y <x) and undoped thickness
0.05 nm active layer 4, thickness of p-type Al _x Ga _1-x As 0.
4 μm 2nd clad layer 5 (Carrier concentration 2 × 10 ¹⁸ cm ^-3 )
Were sequentially grown by MOCVD, and then 0.01 μm thick cap layer 6 made of p-type GaAs (carrier concentration 2 × 10 ¹⁸ cm ^-3 ).
Are sequentially formed. A 0.15 μm thick layer of silicon dioxide is laminated thereover.

A stripe-shaped silicon oxide mask 7 having a width of 5 μm is formed by ordinary patterning (see FIG. 2).
(A)). This mask has an angle of 0 with respect to the <011> direction.
It has a stripe shape that is inclined (turned off) by about 6 ° (see FIG. 1). Then, using the silicon oxide mask 7 as a mask for selective growth, a 0.15 μm-thick n-type GaA film is formed by reduced pressure metalorganic chemical vapor deposition (MOCVD).
s (carrier concentration 8 × 10 ¹⁸ cm ^-3 ) current blocking layer 8
Are formed (FIG. 2B). Then, the silicon oxide mask 7 is removed, and the third cladding layer 9 (carrier concentration 2 × 10 ¹⁸ cm ⁻³ ) made of p-type Al _x Ga _1-x As having a thickness of 1.1 μm,
A contact layer 10 (carrier concentration 8 × 10 ¹⁸ cm ⁻³ ) made of GaAs having a thickness of 5 μmp is sequentially formed, and finally, an n-type electrode 11 is formed on the back surface of the wafer and a p-type electrode 12 is formed on the contact layer 10 (FIG. 2 (c)).

After the above manufacturing process, individual laser elements are obtained by cleaving the wafer (parallel to the paper surface of FIG. 2) into bars and then scribing the bars. In addition,
The operating current flows through the stripe S that is the third cladding layer between the current blocking layers 8 and does not flow in the current blocking layers 8. A semiconductor laser device was manufactured using a mask in which the OFF angle of the stripe S was changed, and the relationship between the OFF angle of the stripe S and the coherence and operating current was examined. FIG. 3 is a graph of the coherence with respect to the OFF angle and the operating current (at an optical output of 3 mW). Coherence decreases with increasing OFF angle, 95%
It can be seen that the following can be achieved when the OFF angle is 1 ° or more.
Also, the operating current increases as the OFF angle increases. Practically, if the upper limit of the operating current is 50 mA, the upper limit of the OFF angle is 3 °.

In the semiconductor laser device manufactured according to this embodiment, by displacing the resonance plane of the laser oscillation resonator, it is possible to oscillate a plurality of modes having different standing wave structures, and the laser light spectrum mode is multi-mode. The mode is set, the coherence is lowered, the influence of the return light from the external optical system is small, and the generation of noise can be reduced. Second Embodiment Next, another embodiment of the present invention will be described.

FIG. 4 is a schematic view of a wafer after the main manufacturing process of another embodiment. (A) a sectional view after forming a silicon dioxide layer mask, (b) a sectional view after growing a current blocking layer, ( c) A cross-sectional view after forming electrodes. The same parts as those in FIG. 2 are designated by the same reference numerals. First, on the n-type GaAs semiconductor substrate 1, a 0.2 μm-thick buffer layer 2 made of n-type AlGaAs and a 1.5 μm-thick first cladding layer 3 made of n-type Al _x Ga _{1 -x} As, Al _y An undoped 0.05-nm-thick active layer 4 made of Ga _1-y As (y <x) and a 0.3-μm-thick second cladding layer 5 made of p-type Al _x Ga _1-x As were successively grown by MOCVD. After that, an etching stop layer E of p-type Al _Z Ga _1-Z As (y <z <x) having a thickness of 0.03 μm is formed, and a thickness of p-type Al _x Ga _1-x As of 1.1 is formed on the etching stop layer E. μm third
A clad layer 9 and a 0.2 μm thick ohmic contact layer 10 made of p-type GaAs are sequentially laminated, and a 0.15 μm thick silicon oxide layer is further laminated.

A stripe-shaped mask 7 having a width of several μm of the silicon oxide layer is formed by an ordinary patterning method (see FIG. 4).
(a)). The stripe direction is 2 from the [011] direction of the substrate crystal.
It was set to OFF. Next, the ohmic contact layer 10 and the third cladding layer 9 are etched using the mask 7. When the etching reaches the etching stop layer E,
It stops automatically and the etching stop layer E remains.

Next, using the silicon oxide mask 7 as a mask for selective growth, a reduced pressure metal organic chemical vapor deposition method (M
By the OCVD method), up to the height of the upper surface of the recontact layer 10,
A current blocking layer 8 made of n-type GaAs is embedded (FIG. 4 (b)).
Finally, the mask 7 is removed and the n-type electrode 11 is placed on the back surface of the wafer.
A p-type electrode 12 is formed on the contact layer 10 and the current blocking layer 8 (FIG. 4 (c)).

As in Example 1, when the semiconductor laser device elements were individually made and the coherence was examined, all the coherence was 95% or less.

[0022]

According to the present invention, by tilting the stripes of the semiconductor laser device by inclining them by 1 ° to 3 ° with respect to the cleavage plane, the laser light spectrum mode becomes a multimode and the coherence can be lowered. it can. As a result, when the semiconductor laser device of the present invention is incorporated into a pickup optical system, it is not affected by the return light from the optical system,
The generation of noise is low, and it is possible to read information with a low error rate.

In such a structure, in the manufacturing process, the pattern of the patterning mask of the silicon dioxide layer may be changed obliquely, the embodiment can be carried out very easily, and the manufacturing yield is high.

[Brief description of drawings]

FIG. 1 is a plan view of a semiconductor laser device according to the present invention.

FIG. 2 is a schematic view of a wafer after a main manufacturing process of a semiconductor laser device according to the present invention, in which (a) a sectional view after forming a silicon dioxide layer mask, (b) a sectional view after growing a current blocking layer,
(C) Cross-sectional views of the semiconductor laser device in the manufacturing process order of the cross-sectional view after electrode formation

FIG. 3 is a graph of coherence with respect to an OFF angle according to the present invention and operating current (at an optical output of 3 mW).

FIG. 4 is a schematic view of a wafer after the main manufacturing process of another semiconductor laser device according to the present invention, (a) a cross-sectional view after forming a silicon dioxide layer mask, (b) a cross-section after growing a current blocking layer. Figures (c) Cross-sectional views of the semiconductor laser device in the manufacturing process order of the cross-sectional view after electrode formation

FIG. 5 is a conventional semiconductor laser device, in which (a) is a plan view and (b) is a sectional view.

[Explanation of symbols]

 1 n-type GaAs semiconductor substrate 2 buffer layer 3 first cladding layer 4 active layer 5 second cladding layer 6 cap layer 7 silicon oxide layer mask 8 current blocking layer 81 current blocking layer boundary 9 third cladding layer 10 contact layer 11 n Side electrode 12 p Side electrode S stripe S1 stripe

Claims (1)

[Claims] To 1. A on the vertical one major surface a cleavage plane of a first conductivity type GaAs substrate, parallel to the main surface of a first conductivity type Al _x
The first cladding layer made of Ga _1-x As, Al _y Ga _{1- y} As (1
>X>y> 0), and a second clad layer made of Al _x Ga _1-x As of a second conductivity type opposite to the first conductivity type, which is laminated in order. In the clad layer, a GaAs current blocking layer of the first conductivity type, which is divided into two, and a third clad layer made of Al _x Ga _1-x As of the second conductivity type, which is closely sandwiched between these two current blocking layers ( stripe)
In the semiconductor laser device provided with,
A semiconductor laser device characterized in that a cross section parallel to the main surface of the cladding layer is a cleavage plane and a parallelogram enclosed by a line oblique to the normal to the cleavage plane.