JPS5944797B2 - Manufacturing method of semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a single mode semiconductor laser device in which an active region is composed of a quantum well type layer.

Conventionally, a single mode semiconductor laser device has a buried heterostructure in which an active region is surrounded by a semiconductor having a large forbidden band width. This buried heterostructure laser device is fabricated using two-step liquid phase growth and mesa etching. In other words, a double heterostructure liquid crystal is created in the first liquid phase growth, and this liquid crystal is then chemically etched to create a mesa structure.
After forming into stripes, the mesa stripes are filled with a semiconductor having a large forbidden band width by a second liquid phase growth. As described above, the manufacturing process of the conventional buried type heterostructure laser device was complicated, and it was difficult to produce 1511 stripes with a width of 1511, resulting in poor product yield. Recently, a semiconductor laser device has been proposed in which the active region is composed of a quantum well type layer in which a large number of two types of semiconductor ultrathin films having different compositions are alternately stacked.

By making the active region a quantum well layer in this way,
It has excellent features such as a lower oscillation current threshold density, less temperature dependence, and the ability to change the wavelength of the oscillated laser light by changing the thickness of the ultra-thin semiconductor film that makes up the quantum well layer. However, when the semiconductor laser device is formed into a buried heterostructure, the manufacturing process is complicated and the product yield is low, as described above. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for easily manufacturing a high-quality semiconductor laser device having a buried heterostructure in which the active region is a quantum well layer.

For this reason, in the present invention, the active layer is formed by an epitaxial growth method using a quantum well layer formed by alternately stacking three or more ultrathin films of two types of compound semiconductors with different compositions, and then the central region of the active layer is Zinc is diffused into the removed left and right regions, and the regions are made to have an average composition of the two types of semiconductors.

The refractive index of the semiconductor having the average composition thus configured is smaller than the refractive index of the active region, thereby confining the laser beam oscillated in the active region in the lateral direction. Therefore, according to the present invention, a buried double-hetero structure semiconductor laser device with a quantum well structure as an active region can be easily manufactured only by zinc diffusion treatment, has little temperature dependence, and can be easily manufactured by stacking semiconductor layers. It has the excellent property that the oscillation wavelength can be changed by changing the thickness. Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 shows an embodiment of the manufacturing process of a semiconductor laser device according to the present invention, in which a Gal-XA layer 2 made semi-insulating by doping oxygen is formed on a semi-insulating substrate crystal 1 made of GaAs or the like. Formed by epitaxial growth method. On this semi-insulating layer 2, a multi-layered layer 3 called a quantum well layer is formed by alternately stacking three or more layers of two ultra-thin compound semiconductor films 5 and 6 with different compositions, each having a thickness of 30 to 100 A. Form. This multilayer stack 3 is used as the active region of the laser device). xA4AspGaAsl-XP
x, GaAsl-XSbx, Inl-GaxAsyPl
It is composed of two compound semiconductors having different binary, ternary, or quaternary compositions such as -. After a predetermined number of multi-layer semiconductor ultrathin films are formed on the semi-insulating layer 2, a semi-insulating Ga, -XAtXAS layer 4 is further formed thereon by epitaxial growth.

The compound semiconductor that becomes the semi-insulating layers 2 and 4 described above is a multilayer stack 3.
A compound semiconductor having a composition larger than the average composition of the two types of compound semiconductors constituting the compound semiconductor is used.

For example, multiple stacks of GaO. 6AtO. 4AS and GaAs
In the case of two types of semiconductors, the average composition means the content rate of At in the whole, and if the thickness and number of layers of the two types of semiconductors are the same, it is 0.2, so the semi-insulating layer 2 , 4 is one containing At least 0.2 or more, for example, GaO. 7AtO. Use 3AS. Semiconductors of vertically opposite conductivity types are used so that the upper semi-insulating layer 4 is of the p-type and the lower semi-insulating layer 2 is of the n-type. In this way, by providing compound semiconductors above and below the active region that have a composition larger than the average composition of the multiple stacked layers, the light induced in the active region due to the difference in refractive index between the two leaks to the outside rather than upward and downward. Never. Next, as shown in FIG. 1, a SiO2 film is attached to the upper surface of the semi-insulating layer 4, and the SiO2 film is removed except for the central part that will become the active region. Zinc is diffused by a closed tube method so as to reach the semi-insulating layer 2 (shaded area in FIG. 2).Since this diffusion of zinc also occurs in the lateral direction, the width of the SiO2 film is determined taking this point into consideration.

Multilayer stack 3 formed of two different compound semiconductors
Among them, the layered state disappears in the region 8 where zinc is diffused,
This is the average composition of the two semiconductors. That is, two semiconductors 5, 6
When GaAs<5Ga0.6At0.4AS is stacked as GaAs<5Ga0.6At0.4AS, the zinc diffused region 8 becomes GaO. 8AtO
．． 2AS, and the central undiffused multilayer of zinc acts as an active region 9 (FIG. 2).

In this way, by setting the composition of the semiconductor 8 in the left and right regions of the active region 9 to the average composition of the two semiconductors constituting the stack, the refractive index becomes smaller than that of the active region, and light is confined in the lateral direction. As a result, a double heterostructure with a buried active region is obtained.

After that, the SiO2 film is removed, and a positive metal electrode 10 is provided on the zinc diffusion region of the semi-insulating layer 4, and a negative metal electrode 11 is provided on the region where zinc is not diffused. A semiconductor laser device as shown in FIG. 2 is obtained by vertically opening both end faces of the multilayer body to serve as reflective surfaces.

As described above, according to the present invention, a buried type semiconductor laser device can be obtained only by zinc diffusion treatment after forming an active layer with a quantum well structure, which eliminates the need for complicated processes such as liquid phase growth and mesa etching. Therefore, a single mode laser can be stably oscillated with good reproducibility without causing variations in the width of the active region. Next, to explain an example of manufacturing the semiconductor laser device of the present invention, a semi-insulating G
Oxygen-doped GaO. 7AtO. ．． 3AS2 with a thickness of 2 μm
On top of this, GaO. 6A! 0.4AS5 and GaAs6 having a carrier concentration of 2.times.10.sup.15 cm.sup.-3 are grown alternately in 6 layers of the former and 5 layers of the latter to a thickness of 50 A by the molecular beam epitaxial method.

Finally, Nf! ). GaO. 7A
tO. 3AS4 (Sn doped, carrier concentration: 7×10
17'3) was grown to a thickness of 1.5 μm by molecular beam epitaxial method.

Next, Si is deposited on the top surface of this n-type semiconductor layer 4 by the CVD method.
O2 was deposited to a thickness of 2000A, and a strip-shaped mask with a width of 6 μm was formed in the center using photolithography.
Others were removed. The gap between the bands was 200 μm. This S
Using the iO2 film as a mask, zinc at about 800° C. was diffused to a depth of 2 μm using a closed tube method. The composition of the zinc-diffused region 8 of the multilayer structure composed of two semiconductors is GaO. 8AtO.
2AS, and the width of the undiffused region that serves as the active region is 2
It was μm.

Thereafter, the SiO2 film is removed, and a metal film 10 made of 00Cr1000A and Au500A is deposited on the zinc-diffused region as a positive electrode, and an ALlGeNi alloy film 11 is deposited as a negative electrode on the region where zinc is not diffused. The strip-shaped laminate thus obtained is opened vertically to serve as a reflective surface, with a length of 300 μm, a width of 200 μm, and a thickness of about 4 μm.
A μm semiconductor laser device was obtained.

The semiconductor laser device thus obtained was a single mode substrate, had a threshold current of 5 mA, and an oscillation wavelength of 7800 A.

The threshold current is expressed as ExpT/TO (T is temperature and TO is a constant), and in a normal semiconductor laser device, TO is 14
Although the temperature is around 0°C, the TO of this laser device is approximately 280°C, indicating that there is little temperature dependence. Note that two types of semiconductor GaO. 6AtO. Among 4AS and GaAs, GaAs
As a result of changing only the layer thickness from 50A to 30A, the oscillation wavelength became 7200A.

[Brief explanation of the drawing]

FIG. 1 is an explanatory view showing the manufacturing process of a semiconductor laser device according to the present invention, and FIG. 2 is a perspective view of the laser device according to the present invention. In the figure, 1 is a substrate crystal, 2 and 4 are semi-insulating layers, 3 is a multilayer stack, 9 is an active region, and 10 and 11 are electrodes.

Claims (1)

[Claims] 1 Zinc is applied to the left and right regions excluding the central region of a laminated active layer formed by alternately stacking three or more layers of two or more compound semiconductor ultrathin films with different compositions of binary, ternary, or quaternary systems. A method of manufacturing a semiconductor laser device, characterized in that the region is made into a semiconductor having an average composition of the two types of semiconductors constituting the active layer by diffusion.