JPH06104527A - Fabrication of semiconductor laser - Google Patents

Abstract

PURPOSE:To fabricate an optical semiconductor element excellent in high temperature characteristics and optical output characteristics with high uniformity and reproducibility. CONSTITUTION:A double, heterostructure including an active layer 3 is formed selectively on the surface of a semiconductor substrate 1, semiconductor block layers 7, 8 are grown while being buried on the opposite sides thereof, and then a semiconductor clad layer 5 and a semiconductor contact layer 6 are laminated on the double heterostructure and the semiconductor block layers. Since the active layer 3 is formed through selective growth, etching of semiconductor is not required and thereby uniformity is improved. Furthermore, since current block layers are formed on the opposite sides of the active layer, an element excellent in high temperature characteristics and optical output characteristics can be obtained.

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 used for optical communication, optical information processing and the like.

[0002]

2. Description of the Related Art Semiconductor lasers used for optical communication and optical information processing have been required to be further mass-produced and reduced in price due to the recent increase in demand. For that purpose, it is important to make the device structure more suitable for mass production and capable of obtaining a high yield.

In order to meet such demands, it is necessary to use a large-area semiconductor wafer and perform crystal growth collectively. As the crystal growth, a vapor phase epitaxy method such as a metal organic vapor phase epitaxy method (MOVPE) which enables large area and high uniform growth is used.

All of the conventionally produced semiconductor lasers for optical communication are manufactured by etching a semiconductor,
The device is manufactured by additional growth. However, if etching is performed on a large-area wafer, the etching shape tends to vary. Therefore, it is difficult to obtain a high yield in device characteristics.

From this background, a method of selectively growing an active layer has been devised as a method of manufacturing a semiconductor laser without etching the semiconductor (Japanese Patent Application No. 03-06).
7498). The manufacturing process of the semiconductor laser based on the invention is shown in FIG. On the surface of the (100) n-type InP substrate 1, a dielectric thin film 21 such as a SiO ₂ film is formed into two parallel stripes in the [011] direction (FIG. 5A).
A double heterostructure composed of an n-type InP clad layer 2, an active layer 3, and a p-type InP clad layer 4 is selectively grown (FIG. 5).
(B)). If the width of the region sandwiched by the SiO ₂ films 21 is set to about 2 μm, the active layer is formed without using mesa etching. Next, the inside of the facing SiO ₂ film 21 is partially removed (FIG. 5C), and the p-type InP clad layer 5 and the p-type InGaAs contact layer 6 are selectively grown so as to cover the active layer (FIG. 5C). 5 (d)). After performing the crystal growth twice in this way, the SiO ₂ film 21 is formed on the entire surface and only the upper side of the active layer is opened (FIG. 5E), and the p-side electrode 31 is formed.
Then, the n-side electrode 32 is formed to form a semiconductor laser (FIG. 5 (f)).

By using this method, the device can be constructed only by patterning and crystal growth of the SiO ₂ film without etching the semiconductor, so that a semiconductor laser excellent in structural uniformity and suitable for mass production can be manufactured.

[0007]

The element structure described above is
Although it is suitable for mass production, the current block structure on both sides of the active layer is formed by InP homojunction, and the current is confined in the active layer due to the difference in built-in voltage from the double heterojunction. ing. for that reason,
The leakage current flowing through the homojunction region increased as the injection current increased, and sufficient high output characteristics could not be obtained.

[0008]

A method of manufacturing a semiconductor laser for solving the above problems is as follows. First
A semiconductor including a step of forming two stripe-shaped growth blocking masks on a conductive type semiconductor substrate, and selectively growing a double heterostructure including a semiconductor active layer in a waveguide region sandwiched by the growth blocking masks. In the laser manufacturing method,
Forming a growth blocking mask on the upper surface of the waveguide region and burying and growing a semiconductor block structure including at least a second conductive type semiconductor block layer and a first conductive type semiconductor block layer on both sides thereof; And a step of forming at least a second conductivity type semiconductor cladding layer on the semiconductor block structure.

On the first conductivity type semiconductor substrate, two stripe-shaped growth-inhibiting masks are formed, and a double heterostructure including a semiconductor active layer is selectively grown in a waveguide region sandwiched by the growth-inhibiting masks. A method of manufacturing a semiconductor laser having a step of forming a growth blocking mask on the upper surface of the waveguide region and burying and growing a semiconductor block structure including at least a high resistance semiconductor block layer on both sides thereof.
And a step of forming at least a second conductivity type semiconductor clad layer on the double hetero structure and the semiconductor block structure.

[0010]

A method of manufacturing a semiconductor laser according to the first aspect of the invention is shown in FIG. 1, and a method of manufacturing a semiconductor laser according to the second aspect of the invention is shown in FIG. Since the active layer is selectively formed as in the conventional structure, the structure has excellent controllability and yield. Further, since both sides of the active layer 3 have a current blocking structure composed of a cyrisk structure or a high resistance layer, the current flowing through the side of the active layer at the time of high injection is extremely small as compared with the conventional structure, and high output characteristics are obtained. Be improved. The structure of the semiconductor laser manufactured by the method shown in FIGS. 1 and 2 is shown in FIGS. 3 (a) and 4 (a) show a mesa structure with improved high-speed response characteristics, but etching for forming the mesa structure does not require particularly high precision, It does not hinder the uniformity of characteristics. In addition, FIGS. 3B and 4B show a structure in which the double hetero structure outside the active region is left, and not only does the mesa etching become unnecessary, but also the turn-on of the current block structure is prevented, and The structure is designed to improve the output operation.

[0011]

As an embodiment corresponding to the invention described in claim 1, the result of manufacturing the structure shown in FIG. 3B by the manufacturing method of FIG. 1 will be described. First, on the surface of the (100) n-type InP substrate 1, the SiO ₂ film 21 (layer thickness 150 n
m) was formed and patterned into two stripes having a width of 5 μm and an interval of 2 μm (FIG. 1A). The stripe direction was [011]. Next, by the MOVPE method, an n-type InP clad layer (carrier concentration 1 × 10 ¹⁸ cm ⁻³ , layer thickness 0.5 μm), InGaAs well (layer thickness 8 nm, 4
Layer) and an InGaAsP barrier (1.3 μm composition, layer thickness 10 nm), a quantum well active layer 3, a p-type InP clad layer (carrier concentration 7 × 10 ¹⁷ cm ⁻³ , layer thickness 0.5).
μm) was selectively grown (FIG. 1 (b)). Then, SiO
_{After the 2} film 21 was once removed, it was formed again on the entire surface, and this time, patterning was performed so as to leave only the active region of the p-InP clad layer formed previously (FIG. 1C). Then, the p-type InP block layer 7 (carrier concentration 7 × 10
¹⁷ cm ⁻³ , layer thickness 0.8 μm) and n-type InP block layer 8 (carrier concentration 2 × 10 ¹⁸ cm ⁻³ , layer thickness 0.8 μ)
m) was selectively embedded and grown (FIG. 1 (d)). Finally,
After removing the SiO ₂ film 21, the p-type InP block layer 5 (carrier concentration 7 × 10 ¹⁷ cm ⁻³ , layer thickness 1 μm) is formed on the entire surface.
And a p-type InGaAs contact layer 6 (carrier concentration 1 × 10 ¹⁹ cm ⁻³ , layer thickness 0.3 μm) were grown (FIG. 1).
(E)). The crystal growth process was performed using a 2-inch InP substrate.

A p-side electrode 31 and an n-side electrode 32 were formed on the surface of the wafer thus formed by crystal growth three times (FIG. 1 (f)). Resonator length of 300 μm due to cleavage
Semiconductor laser. When the characteristics of the cut out 200 devices were measured, the oscillation threshold current was 18.7 on average.
The deviation was 2.1 mA and the deviation was 2.1 mA, and the oscillation wavelength at the time of 5 mW light output was 1547 nm on average and the deviation was 8.8 nm, showing high uniformity. The maximum output during continuous operation at 25 ° C. was 62 mW on average, and 78 out of 100 recorded an optical output of 50 mW or more. On the other hand, the maximum output of the device manufactured by the conventional structure was 38 mW, and it was confirmed that the high output characteristics were improved by this structure.

Next, the result of manufacturing the semiconductor laser of FIG. 4A using the manufacturing method of FIG. 2 based on the invention described in claim 2 will be described. The difference from the semiconductor laser described above is that in the process of buried growth in FIG. 2D, the current block structure is a high resistance InP block layer 9 (Fe-doped, Fe concentration 1 × 10 ¹⁶ cm ⁻³ , layer thickness 2 μm). ) And n
Type InP layer (carrier concentration 4 × 10 ¹⁸ cm ⁻³ , layer thickness 0.
6 μm). In addition, width 4μm, depth 3μ
Two mesa grooves 22 having a pitch m of 15 μm were formed. This element was also evaluated on 100 pieces cut out from a 2-inch wafer, and the threshold current was 16.2 m on average.
A, the deviation was 2.6 mA, and 85 light outputs of 30 mW or more were obtained. When the frequency response characteristics of 30 of these were measured, the average was 1 as the band at 30 mW or more.
5 GHz was obtained. As described above, since this element has a high resistance block structure, good high frequency characteristics could be obtained with good uniformity.

[0014]

As described above, according to the semiconductor laser manufacturing method of the present invention, a structure in which both sides of the selectively formed active layer are filled with a current block structure can be manufactured, so that high output characteristics and high frequency characteristics can be obtained. It has a feature that an excellent semiconductor laser can be mass-produced with good uniformity.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a method for manufacturing a semiconductor laser according to claim 1.

FIG. 2 is a sectional view showing an embodiment of the method for manufacturing the semiconductor laser according to claim 2;

3 is a sectional view showing the structure of a semiconductor laser manufactured by the method of FIG.

4 is a sectional view showing the structure of a semiconductor laser manufactured by the method of FIG.

FIG. 5 is a cross-sectional view showing a conventional method for manufacturing a semiconductor laser.

[Explanation of symbols]

1 n-InP substrate 2 n-InP clad layer 3 active layer 4 p-InP clad layer 5 p-InP clad layer 6 p-InGaAs contact layer 7 p-InP block layer 8 n-InP block layer 9 high-resistance InP block layer 10 n-InP layer 21 SiO ₂ film 22 Mesa groove 31 p-side electrode 32 n-side electrode

Claims (2)

[Claims] 1. A double-hetero structure in which two stripe-shaped growth blocking masks are formed on a first conductivity type semiconductor substrate and a semiconductor active layer is selectively formed in a waveguide region sandwiched by the growth blocking masks. In the method of manufacturing a semiconductor laser having a step of growing a semiconductor block structure, a growth block mask is formed on the upper surface of the waveguide region, and a semiconductor block structure including at least a second conductive type semiconductor block layer and a first conductive type semiconductor block layer on both sides thereof. And a step of forming at least a second conductivity type semiconductor clad layer on the double hetero structure and the semiconductor block structure. 2. A double heterostructure having two stripe-shaped growth stop masks formed on a first conductivity type semiconductor substrate and having a semiconductor active layer in a waveguide region sandwiched by the growth stop masks selectively. In the method of manufacturing a semiconductor laser having a step of growing a semiconductor block structure on the upper surface of the waveguide region and burying and growing a semiconductor block structure including at least a high resistance semiconductor block layer on both sides of the growth block mask, And a step of forming at least a second conductivity type semiconductor clad layer on the hetero structure and the semiconductor block structure.