JPS6354236B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a semiconductor laser, particularly a distributed feedback semiconductor laser using a compound semiconductor.

[Technical background of the invention and its problems]

In recent years, distributed feedback semiconductor lasers (hereinafter abbreviated as DFB lasers) have been developed as light sources for optical transmission in place of conventional Fabry-Perot semiconductor lasers. To manufacture a DFB laser, it is necessary to grow multiple layers of GaInAsP, InP, etc. on an InP substrate on which a diffraction grating, which is a periodic uneven structure, is formed. Conventionally, to form these layers on a diffraction grating, crystal growth is performed at a temperature of 600 [℃] or higher, but with this method, the diffraction grating is deformed due to dissociation of P before crystal growth begins. Undesirable.

Recently, attempts have been made to grow crystals at temperatures below 600 degrees Celsius. In this method, since the degree of dissociation of P is significantly reduced, crystal growth can be performed on the diffraction grating without substantially deforming it. However, GaInAsP with a bandgap wavelength of around 1.3 [μm] at a growth temperature below 600 [℃]
When attempting to grow an active layer, it may grow in the region where the GaInAsP miscibility gap exists, making it difficult to obtain a film with good crystallinity. For this reason, there has been a problem that the oscillation threshold of the DFB laser tends to become high.

[Purpose of the invention]

An object of the present invention is to provide a method for manufacturing a semiconductor laser that can grow an active layer with good crystallinity without causing deformation of the diffraction grating, and that enables low threshold oscillation of a DFB laser. It is in.

[Summary of the Invention] The gist of the present invention is to grow an optical waveguide layer at a low temperature on a substrate on which a diffraction grating is formed, and to grow an active layer on the optical waveguide layer at a high temperature.

That is, the present invention provides a method for manufacturing an InP/GaInAsP semiconductor laser, in which a diffraction grating with a predetermined period is formed on an InP substrate, and then Ga _x In _1-x As is formed on the substrate at a temperature of 600 [°C] or less. _y P _1-y optical waveguide layer is grown and then Ga _x ′In _1-x ′As _y ′P _1-y ′(x′>x,
y′>y) This is a method in which the active layer is grown and formed.

〔Effect of the invention〕

According to the present invention, since the optical waveguide layer is grown on the diffraction grating at a temperature of 600 [° C.] or lower, the diffraction grating is not deformed during the formation of this grown layer. Furthermore, since the active layer is grown at a temperature exceeding 600 [° C.], the active layer can have good crystallinity. Therefore, the oscillation threshold can be reduced. Furthermore, compared to conventional methods, this method has the advantage that it can be easily implemented by simply changing the growth temperature.

[Embodiments of the invention]

Figures 1a to 1c relate to an embodiment of the present invention.
FIG. 3 is a cross-sectional view showing a DFB laser manufacturing process. first,
As shown in Figure 1a, the period 2000 is
[Å], and a depth of 800 [Å] was formed. Next, as shown in FIG. 1b, n-InP substrate 1 is
-Ga _0.14 In _0.86 As _0.31 P _0.69 layer (optical waveguide layer) 3 to 0.2
[μm] grew and formed. This optical waveguide layer 3 is formed using a liquid phase growth method, and as shown in FIG.
After soaking the substrate 1 at 600 [°C], crystal growth was started at time t ₁ (temperature 588°C). At this time,
Since the growth temperature is 600 [° C.] or lower, almost no deformation of the diffraction grating 2 occurs.

Immediately after the optical waveguide layer 3 was grown and formed, the temperature of the substrate 1 was raised and maintained at 670 [°C] to make the melt uniform.
Crystal growth started again at time t ₂ (temperature 646°C). That is, as shown in FIG. 1c, an n-InP layer (buffer layer) 4 and a Ga _0.26 In _0.74
An As _0.56 P _0.44 layer (active layer) 5, a P--InP layer (cladding layer) 6, and a P--Ga _0.16 In _0.84 As _0.36 FP _0.64 layer (cap layer) 7 were successively grown. At this time,
Since the active layer 5 is grown at a temperature exceeding 600[° C.], it has good crystallinity. Also, 600
Even if the temperature exceeds [° C.], the top of the diffraction grating 2 is covered with the optical waveguide layer 3 due to the previous growth process, so there is no risk that the diffraction grating 2 will be deformed during this growth process.

When the wafer thus produced was evaluated,
There is a depth at the interface between the n-InP substrate 1 and the optical waveguide layer 3.
A diffraction grating 2 of 800 [Å] was observed. Further, the buffer layer 4 is 0.1 [μm], the active layer 5 is 0.2 [μm], the cladding layer 6 is 2 [μm], and the cap layer 7 is 1 [μm], and the photoluminescence intensity of the active layer 5 is 600
It was several times stronger than those grown at temperatures below [°C]. Striped electrodes were attached to this wafer, devices were made by cleavage, and their characteristics were investigated.
DFB oscillation was obtained. This will convert all layers to 600
This value is 1/2 of the threshold value of 200 [mA] obtained when manufacturing at a low temperature below [℃].

As described above, according to the method of this embodiment, the optical waveguide layer 3 is grown and formed at a low temperature of 600 [°C] or lower (588°C),
Since the active layer 5 is grown and formed at a temperature exceeding 600 [°C] (646°C), the active layer 5 of good quality can be formed without causing deformation of the diffraction grating 2.
Therefore, both diffraction efficiency and luminous efficiency are improved,
Low threshold DFB oscillation can be achieved.

Note that the present invention is not limited to the embodiments described above. For example, the growth temperature of the optical waveguide layer is not limited to 588 [°C], but may be 600 [°C].
It may be determined as appropriate within the following range. Similarly, the growth temperature of the active layer may be appropriately set within a range exceeding 600 [°C]. Further, the compositions of the active layer and the optical waveguide layer are not limited to those in the embodiments, and can be changed as appropriate. However, the present invention is most effective when the band gap wavelength λ _B ′ is 1.20 [μm]≦λ _B ′≦1.35.
[μm] luminescent layer (GaInAsP active layer)
This is the case when growing. Therefore, the composition of the Ga _x ′In _1-x ′As _y ′P _1-y ′ layer forming the active layer is (0.20
≦x′≦0.29, 0.43≦y′≦0.63). Furthermore, the bandgap wavelength λ _B of the optical waveguide layer is set so that the laser oscillation light is not absorbed.
The appropriate range is 1.05 [μm]≦λ _B ≦1.25 [μm],
Therefore, the optical waveguide layer Ga _x In _1-x As _y
The composition of the P _1-y layer is (0.10≦x≦0.23, 0.21≦y≦
0.50, x<x', y<y'). Furthermore, the conductivity types of the substrate and each layer can be reversed. In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of the drawing]

Figures 1a to 1c relate to an embodiment of the present invention.
A cross-sectional view showing the DFB laser manufacturing process, and FIG. 2 are schematic diagrams showing processing temperature changes in the above example process. 1...n-InP substrate, 2...diffraction grating, 3...n-
GaInAsP layer (optical waveguide layer), 4...n-InP layer (buffer layer), 5...GaInAsP layer (active layer), 6...P
-InP layer (cladding layer), 7...P-GaInAsP layer (cap layer).

Claims (1)

[Claims] 1. A step of forming a diffraction grating with a predetermined period on an InP substrate, and then forming a Ga _x In _1-x As _y P _1-y optical waveguide layer on the substrate at a temperature of 600 [°C] or less. Ga _x ′In _1-x ′As _y ′P _1-y ′ (x′>x, y′>y
)
1. A method for manufacturing a semiconductor laser, comprising the step of growing an active layer directly or via a buffer layer. 2. The method of manufacturing a semiconductor laser according to claim 1, wherein the compositions of the optical waveguide layer and the active layer are set as follows. (0.10≦x≦0.23, 0.21≦y≦0.50 0.20≦x′≦0.29, 0.43≦y′≦0.63)