JP2924435B2 - Semiconductor laser and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a semiconductor laser used for a light source such as a laser printer or a bar code reader, and more particularly to a method for manufacturing a visible light semiconductor laser having an oscillation wavelength of 680 nm or less.

[0002]

2. Description of the Related Art A conventional method for manufacturing a semiconductor laser will be described below. The structure of the semiconductor laser is shown in the figure.
The first crystal growth is performed at a temperature of 620 ° C. by metal organic chemical vapor deposition (hereinafter referred to as MOVPE), and n
An active layer 4 is formed by inserting cladding layers 3 and 5 on a GaAs substrate 2 having a rectangular shape. The n-type GaAs substrate 1 has a so-called “(100) 5 ° offward (011)” in which the substrate surface is oriented in the direction of (011) by 50 from (100).
Of shape. The active layer 4 serves as a light emitting region,
It has the structure of a _0.5 In _0.5 P. The forbidden band width of the cladding layers 3 and 5 is larger than that of the active layer, and (Al _0.5 Ga
_0.5 ) _0.5 In _0.5 P A double hetero structure is formed by cladding layers 3 and 5 in which active layer 4 is inserted.

Next, in order to form a selective growth mask also serving as an etching mask for forming a ridge stripe, a film is formed using an oxide film. 0 by photoresist method
<< 1 >> An oxide film stripe is formed in the direction of <1>, and the P-clad layer 5 is etched by an etching method so as to leave 0.2 μm, and is removed. <<>> is <<>>
It is used as a symbol indicating the direction opposite to the size of the direction described in. Subsequently, the second crystal growth is performed by a selective growth method using the oxide film as a mask. Thereby, the current blocking layer 7 is grown. Subsequently, after removing the oxide film, a P-GaAs contact layer 8 is grown on the front surface, and electrodes 9 and 10 are attached to obtain a semiconductor laser.

In the conventional example, GaAs “(100)
The reason for using the 5 ° offward (011) ”substrate is to reduce the hillock density. Table 1 at the end of [Detailed Description of the Invention] shows the relationship between the hillock density and the plane orientation. In a semiconductor laser having a cavity length of 300 μm,
Oscillation threshold current is 50 mA, oscillation wavelength is 663-66
A characteristic of 7 nm is obtained. Output 3m at a temperature of 40 ° C
It has been confirmed that the reliability is good in the energized state of W. The details of this conventional example are shown on page 57 of the IEICE Technical Meeting ED89-106.

[0005]

The problems to be solved are the following points. That is, "(10
In the case of using a 0) just "substrate, it is difficult to fabricate a semiconductor laser because the hillock density is too high. In addition," (100) 5 ° off "of GaAs having a low hillock density
When a forward (011) "substrate is used, the shape of the ridge stripe is not bilaterally symmetric, so that the lateral spread of the injection current is asymmetric, and the formed gain region and lateral refractive index distribution are asymmetric.

Further, the peak position of the intensity of the beam emitted from the end face shifts with the change of the light output. Also, due to this asymmetry, the range of the ridge stripe width in which desired laser characteristics can be obtained is narrowed. Furthermore, GaAs "(10
0) When a 5 ° offward (011) ”substrate is used, a substrate having a surface where the doping efficiency to the P-cladding layer is just (100) in the crystal growth step, ie,“ (100) ” Since it is two to three times as large as the “just” substrate, it becomes difficult to control the carrier concentration.

[0007]

Means for Solving the Problems] To solve the above problems
The semiconductor laser according to the present invention is an n-type GaAs (10
0) a substrate, formed on the GaAs (100) substrate
n-type _{(Al y Ga (1-y} )) 0.5 I n 0.5 P (0.
5 ≦ y ≦ 1) a first cladding layer having a structure,
1 is formed on the cladding layer 1 and becomes a light emitting region (Al _x G
a ( _1-x )) _0.5 In _0.5 P (0 ≦ x ≦ 0.3) Structure
An active layer having a P-type (A) formed on the active layer.
_{l y Ga (1-y)} ) a second having the structure _0.5 an In _0.5 P
With a double heterostructure consisting of
The n-type first cladding layer and the active layer are formed at a growth temperature.
Of GaInP lattice-matched on the GaAs substrate.
Set the temperature above the temperature at which the forbidden band becomes a minimum, and set the crystal growth rate
Is set at 1 to 2.5 μm / h to grow
The p-type second metal is formed by a metal organic chemical vapor deposition method.
The growth temperature of the lad layer is limited by the band gap of GaInP.
Set the temperature to a small temperature and increase the growth rate to 2.5 μm / h or more
By metalorganic vapor phase epitaxy
It is formed. Also, a semiconductor laser according to the present invention
Is manufactured on an n-type GaAs (100) substrate.
Of _{(Al y Ga (1-y} )) 0.5 In 0.5 P (0.5 ≦ y
<1) a first step of growing a first cladding layer
And a light emitting region on the first cladding layer (Al
_{x Ga (1-x))} 0.5 In 0.5 P of (0 ≦ x ≦ 0.3)
A second step of growing an active layer;
P-type of _{(Al y Ga (1-y} )) 0.5 In 0.5 P structure
A third step of forming a second cladding layer having
The n-type first cladding layer and the active layer
The first and second steps of forming a layer include:
Prohibition of GaIn P lattice-matched on the GaAs substrate
Set the temperature at or above the temperature at which the band width is minimal, and set the crystal growth rate to 1
２．５2.5 μm / h, and metalorganic vapor phase epitaxy
And form the P-type second cladding layer
The third step is to set the growth temperature to the above-mentioned
Set the temperature at which the stop zone width is minimal, and set the growth rate to 2.5μ.
m / h or more and grown by metal organic chemical vapor deposition
Things.

[0008]

Next, the present invention will be described with reference to the drawings. 1, the "(100) just" substrate of GaAs, the growth rate of 1.5 [mu] m / h and _{1.0μm / h (Al y Ga (} 1-y)) 0.5 In 0.5 P (y = 0. The growth temperature dependence of the hillock density when growing 6) is shown.
The hillock density can be reduced by increasing the growth temperature and decreasing the growth rate in this manner.
As described above, since the hillock density depends on the growth temperature and the growth rate, it can be said that the supply amount of Group III and the decomposition efficiency are closely related.

[0009] A growth temperature of low hillock density, for example, 70
A semiconductor laser having a double heterostructure formed at a growth temperature of 0 ° C. could not obtain sufficient reliability. this is,
P- and reduction of the carrier concentration of the _{(Al y Ga (1-y} )) 0.5 In 0.5 P clad layer, due to the crystallinity degradation of the active layer due to diffusion of the dopant activation layer. Also, (Al _y Ga ( _1-y )) is formed on a GaAs “(100) just” substrate.
_0.5 In _0.5 P is grown at a low hillock density growth temperature. Subsequently, the temperature was lowered to (AlGa ( _1-y )) _0.5 In
The hillock density when _0.5 P is grown is almost the same as the hillock density of the underlying layer.

A method for manufacturing the semiconductor laser shown in FIG. 2 will be described based on these results. First, the first final growth was performed by MOVPE method, and the growth pressure was 30 torr.
Set to r. "(100) just" of n-type GaAs
On the substrate, an n-type GaAs buffer layer 22 doped with Si is grown at a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ over 0.4 μm. Next, M-type (Al
_{A 0.6} Ga _0.4 ) _0.5 In _0.5 P cladding layer 3 is grown over 1 μm at a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ . Further, the undoped Ga _0.5 In _0.5 P active layer 4 is
Grow over 7 μm. At this stage, the growth temperature has been set at 700 ° C., and the growth rate has been set at 1.5 μm / h. After growing the active layer 4, the growth temperature is lowered from 700 ° C. to 660 ° C. while supplying PH ₃ .

The interruption time is set to 10 minutes or less. After the temperature was stabilized at 660 ° C., Zn-doped P- (A
l _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 5 is deposited over 1 μm at a carrier concentration of 3.5 × 10 ¹⁷ cm ⁻³ , and then a Zn-doped P—Ga _0.5 In _0.5 P heterobuffer layer 6 is deposited at a carrier concentration of 3.5 × 10 ¹⁷ cm ^−3. Deposit at 1 × 10 ¹⁸ cm ⁻³ over 0.1 μm. The growth rate in the latter half is 2.8 μm
/ H. FIG. 3 shows the growth temperature sequence up to this point.

Here, the growth rate in the process after the p-cladding layer 5 was 2.8 μm / h. This was performed for the purpose of improving the efficiency of incorporating Zn as a dopant into the solid phase. By increasing the growth rate in this way,
The growth time and the time maintained at a high temperature are shortened, and the diffusion of the dopant is suppressed. In the MOVPE apparatus according to the present invention, the growth temperature at which the band gap of Ga _0.5 In _0.5 P is minimized is 660 ° C.

Subsequently, SiO ₂ serving as a selective growth mask also serves as an etching mask for forming a ridge stripe.
An oxide film is formed to a thickness of 0.2 μm, a SiO ₂ oxide film stripe is formed in a 0 << 1 >><< 1 >> direction by a photoresist method, and a p-cladding layer 5 is formed by a sulfuric acid-based etchant by 0.25 μm. Perform etching with leaving. The ridge width W is limited to 4 to 5 μm.

Next, the second crystal growth is performed on both sides of the ridge stripe at a growth temperature of 650 ° C. by the MOVPE method. Thus, n-type GaAs doped with Si by the selective growth method using the SiO ₂ oxide film as a mask.
The s-current blocking layer 7 has a carrier concentration of 3 × 10 ¹⁷ cm ⁻³
Is formed over 0.8 μm. Growth rate is 3μm
/ H. After removing the Si oxide film, a third crystal growth is performed on the entire surface at a growth temperature of 650 ° C. by MOVPE. Thereby, Zn-doped P-Ga
The As contact layer 8 has a carrier concentration of 2 × 10 ¹⁹ cm ^−3.
Is formed over 3 μm. Thereby, the electrodes 9, 1
0 is formed, and the semiconductor laser of the present invention is obtained.

The characteristics of the semiconductor laser are as follows.
m, oscillation threshold 40-45mA, oscillation wavelength 673nm
It is. Further, an element having an MTF of 20,000 hours or more was obtained at a high yield under a constant-current output condition of a case temperature of 50 ° C. and an optical output of 5 mW. Other structures, for example, FIG.
The same manufacturing method can be applied to the semiconductor laser described above. Further, the active layer 4 serving as a light emitting region is made of Ga _0.5 In _0.5 P and (A
by using the _{l Z Ga (1-Z)} ) 0.5 In 0.5 P (0 <Z ≦ 0.5), may be constituted by a multiple quantum well structure.

[0016]

As described above, in the present invention, GaAs is used.
s (100) on the substrate n- clad layer 3, in forming a double heterostructure of the active layer 4 and the P- cladding layer 5, that the band gap of Ga _0.5 In _0.5 P is grown temperature dependence Considering the above, the n-cladding layer 3 and the active layer 4 are grown at a temperature equal to or higher than the temperature at which the forbidden band width is minimized.
Grow at 2.5 μm / h. Further, the p-cladding layer 5
Is deposited at a temperature at which the band gap of Ga _0.5 In _0.5 P is minimized, whereby the hillock density is kept low and the yield of the device is greatly improved. In addition, by increasing the crystal growth rate to 2.5 μm / h or more in the process after the formation of the p-cladding layer 5, the efficiency of incorporation of Zn into the crystal of the dopant is increased, and the diffusion of the dopant into the active layer 4 is suppressed. Can be suppressed. These processes have the effect of significantly improving the reliability of the semiconductor laser.

[Table 1]

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a relationship between a growth temperature and a hillock density according to the present invention.

FIG. 2 is a sectional view showing a structure of one embodiment of a semiconductor laser according to the present invention.

FIG. 3 is an explanatory view showing a temperature sequence according to a method for manufacturing a semiconductor laser according to the present invention.

FIG. 4 is a sectional view showing the structure of another embodiment of the semiconductor laser according to the present invention.

FIG. 5 is a cross-sectional view showing a structure of a semiconductor laser according to a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 3,5 Cladding layer 4 Active layer 6,21,22 Buffer layer 7 Current block layer 8 Contact layer 9,10 Electrode

Claims (2)

(57) [Claims] 1. An n-type GaAs (100) substrate, and an n-type (Al) formed on the GaAs (100) substrate.
a first cladding layer having a _{y Ga (1-y))} 0.5 In 0.5 P (0.5 ≦ y ≦ 1) structure, is formed on the first cladding layer on a light emitting region (A
_{l x Ga (1-x)} ) 0.5 In 0.5 P (0 ≦ x ≦ 0.3 and an active layer having a structure), is formed on the active layer P-type _{(Al y Ga (1-y} ))
I and a second cladding layer having a structure of _0.5 an In _0.5 P
The n-type first cladding layer and the active layer have a GaI lattice-matching growth temperature on the GaAs substrate.
Set the temperature above the temperature at which the band gap of nP becomes minimal, and
Growing at a long speed of 1 to 2.5 μm / h
Formed by metal organic chemical vapor deposition and the p-type second
The growth temperature of the cladding layer is set to a temperature at which the band gap of GaInP is minimized.
At a growth rate of 2.5 μm / h or more.
What was formed by metalorganic vapor phase epitaxy by lengthening
A semiconductor laser characterized by the above-mentioned . 2. An n-type GaAs (100) substrate having an n-type
Of _{(Al y Ga (1-y} )) 0.5 In 0.5 P (0.5 ≦ y ≦
1) First step of growing a first cladding layer
And a light emitting region (Al _x G) on the first cladding layer.
a ( _1-x )) _0.5 In _0.5 P (0 ≦ x ≦ 0.3)
A second step of growing, the P type on the active layer _{(Al y Ga (1-y} )) 0.5 In 0.5
Third forming a second cladding layer having a structure of P
It consists of a step, to form a first cladding layer and the active layer of the n-type
The first and second steps are performed by adjusting the growth temperature to a GaI lattice-matched on the GaAs substrate.
Set the temperature above the temperature at which the band gap of nP becomes minimal, and
Set the long speed to 1 to 2.5 μm / h and
The P-shaped second crack
In the third step of forming a doped layer , the growth temperature is set to a temperature at which the band gap of GaInP is minimized.
And the growth rate is set to 2.5 μm / h or more.
A method for manufacturing a semiconductor laser, wherein the semiconductor laser is grown by a metal vapor phase epitaxy method.