JPH02174180A - Manufacture of distributed reflection type semiconductor laser - Google Patents

Abstract

PURPOSE:To prevent optical reflection and scattering in the junction part by a method wherein a mask area is minimized, and an active waveguide path layer and an non-active waveguide layer, whereon a grating having the uniform pitch and depth is formed, are connected by a vapor phase epitaxial method while being optically matched and collated. CONSTITUTION:An active waveguide path layer 2 and a protective layer 3A having the thickness, wherein the thickness of the layer 2 is deducted from the thickness of a non-active waveguide path layer 3 being optically matched and connected with the layer 2, are in order laminated on an n-type semiconductor substrate 1 and thereon an insular prescribed region 3B, whose area is as much as possible minimized, is formed, while forming a non-active waveguide path layer 3 whose thickness is equal to that of a laminated construction and which has an almost flat top side is formed by a vapor epitaxial growth method only on the region, where the laminated construction except the region 3B is removed, next, a grating 10 is formed on the top of the protective layer 3A and the layer 3, further on their top side, a p-type clad layer 4 is formed of the same material with the protective layer 3A. Thereby, the thickness of the non-active waveguide path layer 3 becomes uniform in the connection part while having good crystallization so as to prevent reflection and scattering in the junction part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a monodistribution reflection type semiconductor laser.

[Prior art]

Traditionally, this type of distributed reflection semiconductor laser has demonstrated stable single-mode operation even during ultra-high-speed modulation at the gigabit/second level, making it suitable for long distances.

It is seen as a promising light source for large-capacity optical fiber communications.

In addition, among this type of distributed reflection semiconductor lasers, in manufacturing high-performance distributed reflection semiconductor lasers with added wavelength control functions, it is necessary to form a diffraction grating in the crystal and provide a control electrode. It is necessary to match and bond a low loss non-active waveguide layer with an active waveguide layer.

As shown in FIG. 6, Tomori et al. formed an active waveguide layer in a predetermined stripe-shaped region 32 on a semiconductor substrate 31 with an inactive waveguide whose thickness optically matches that of the active waveguide layer. A layered structure is formed by sequentially layering a protective layer that is approximately equal to the thickness of the layer minus the thickness of the active waveguide layer,
An inactive waveguide layer having a thickness substantially equal to that of the layered structure and having a substantially flat top surface is formed by vapor phase epitaxial growth only in regions other than the region where the layered structure is formed on the semiconductor substrate.

An attempt was made to solve this problem by forming a diffraction grating on the upper surface of the protective layer and the inactive waveguide layer, and further forming a cladding layer made of the same material as the protective layer on the upper surface of the diffraction grating. (Sho 62-178978).

[Problem to be solved by the invention]

However, in the above-mentioned conventional technology, the thickness of the non-active waveguide layer gradually changes at the coupling portion, making it impossible to form a uniform diffraction grating when attempting to form a diffraction grating on the top surface. There was a problem in that it was difficult to obtain a non-active waveguide layer with good crystallinity.

In other words, since the thickness of the non-active waveguide layer is not uniform in the coupling part and the crystallinity is poor, reflection and scattering occurs in the coupling part, which not only causes loss but also decreases the optical output and increases the laser threshold. There was a problem in that the value increased.

Furthermore, there is a possibility that a problem may arise in the reliability of the device.

The present invention has been made to solve the above problems.

An object of the present invention is to provide a technique that can eliminate as much as possible the non-uniformity of the thickness of the non-active waveguide in the coupling portion.

Another object of the present invention is to provide a technique that can enhance the coupling between different types of waveguides by improving crystallinity and achieve higher performance.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means to solve the problem]

To achieve the above object, the present invention provides a method for manufacturing a distributed reflection semiconductor laser, including an active waveguide layer on a semiconductor substrate having a first conductivity type, and an active waveguide layer optically aligned with the active waveguide layer. A laminated structure is formed by sequentially laminating an inactive waveguide layer that is coupled to the inactive waveguide layer, and a protective layer having a thickness substantially equal to the thickness of the inactive waveguide layer minus the thickness of the active waveguide layer. forming a predetermined island-like region on the laminated structure on the semiconductor substrate, removing the laminated structure other than the predetermined island-like region, and adding the laminated structure only to the predetermined island-like region; a second step of forming a non-active waveguide layer having a thickness substantially equal to that of the multilayer structure on the semiconductor substrate other than the region where the multilayer structure is formed, and forming an inactive waveguide layer having a substantially flat upper surface by vapor phase epitaxial growth. a fourth step of forming a diffraction grating on the upper surface of the protective layer and the inactive waveguide layer; and a second conductive layer made of the same material as the protective layer on the upper surface of the diffraction grating. The most important feature is that it includes a fifth step of forming a cladding layer having a mold.

[Effect]

According to the above-mentioned means, in vapor phase epitaxial growth, migration of growth species on the surface of the semiconductor substrate is rapid and flatness is good. Sun
Even in selective growth using a mask such as , etc., the growing species that arrive on the mask quickly move onto the semiconductor substrate (area not covered by the mask), and then move to the vicinity of the edge of the mask and away from the mask. The effect of suppressing the concentration gradient of growing species at a point is remarkable.

Therefore, a selectively grown layer with a flat top surface can be obtained. However, if the mask area occupied on the semiconductor substrate is large, it becomes difficult to obtain these effects, so by making the mask area as small as possible, the effects become even more remarkable.

[Embodiments of the invention]

An embodiment of the present invention will be specifically described below with reference to the drawings.

Note that throughout the description of the embodiments, parts having the same functions are given the same reference numerals, and repeated explanations thereof will be omitted.

[Example ■]

FIG. 1 is a perspective view showing a schematic configuration of Example I of a distributed reflection semiconductor laser manufactured by applying the present invention.

In FIG. 1, 1 is an n-type InP substrate, 2 is an InGaAsp active waveguide layer with a wavelength λ0 of 1.55 μm, and 3 is a wavelength λ. is a 163 μm n-type InGaAsP non-active waveguide layer, 4 is a p-type InP cladding layer, and 5 is a p''''-type InGa layer.
AsP cap layer, 6 p-type InP current blocking layer, 7
is an n-type InP current confinement layer, 8 is an n-type electrode, 9 is a p-type electrode, 10 is a diffraction grating with a pitch layer of about 2,400 layers and a depth of about 500 layers, and 11 is the active waveguide layer 2 and the inactive waveguide. This is the joint part with layer 3.

Note that the wavelength λ. indicates the bandgap wavelength of the medium.

An active region 101 including an active waveguide layer 2 and a diffraction grating 10
A distributed reflection (DBR) region 102, 103 with a non-active waveguide layer 3 and a phase adjustment region 104 with a non-active waveguide layer 3 are electrically separated.

FIGS. 2A to 2F show an example of fabricating the distributed reflection semiconductor laser shown in FIG. 1 by applying the manufacturing method of the present invention.
FIG.

As shown in FIG. 2A, the method for manufacturing the distributed reflection type semiconductor laser of Example 2 is as follows: First, as shown in FIG. 2A, an active waveguide layer (0.15 μm thick, band Gap wavelength λ: 1.55μ
m) 2, protective layer made of InP (thickness 0.1 μm) 3A
are successively formed in contact with each other using a metal organic vapor phase epitaxial growth (MOVPE) method.

Next, as shown in FIG. 2B, this n-type InP substrate 1
A SiO□ mask 3B is placed on the protective layer 3A as a predetermined area.
1 using, for example, a sputtering method and a photolithography method, and unnecessary portions of the active waveguide layer 2 and the protective layer 3A are removed using this SiO□ mask 3B and, for example, a chemical etching method. An island region (3B) having a length of about 200 μm and a width of about 40 μm is formed in the (011) direction as shown in FIG. 2B.

Next, as shown in FIG. 2C, the 5in2 mask 3B
As a selective growth mask, an inactive waveguide layer (thickness 0.25 μm, band gap wavelength 1.3 μm) 3 made of non-doped 1nGaAsP is grown only in regions other than the island-like region.
is formed using the MOVPE method.

In this case, the pressure inside the reactor is set to about 50 T as a forming condition.
Since the orr is extremely low compared to atmospheric pressure, the raw material gas moves quickly on one surface of the n-type InP substrate.

The effect of obtaining a flat growth surface is further promoted.

Therefore, no growth occurs on the SiO□ mask 3B,
A flat growth surface as shown in FIG. 2C is obtained.

Next, after removing the SiO□ mask 3B with HF or the like, the second
As shown in Figure D, a diffraction grating 10 with a pitch of about 2,400 gratings and a depth of about 500 gratings is formed over the entire surface of the protective layer 3A and the inactive waveguide layer 3 using a two-beam interference exposure method and a chemical etching method. . In this case, the upper surfaces of the protective layer 3A and the inactive waveguide layer 3 can be made flat by the MOVPE method.

Next, as shown in FIG. 2E, p-type I is placed on the diffraction grating 10.
MOV the cladding layer (thickness 2.0 μm) 4 made of nP
Formed by PE method or the like. In this case, the cladding layer 4
Since the same InP as the protective layer 3A is used,
The diffraction grating 10 formed on the protective layer SA is essentially the same as that which has disappeared, as shown in FIG. 2F.

Finally, a buried structure for transverse mode control is formed by dry etching and MOVPE, and as shown in FIG. Distributed reflection (D
BR) area 102.103.

The phase adjustment region 104 having the inactive waveguide layer 3 is electrically separated, and a p-type electrode and an n-type electrode are respectively formed to complete a distributed reflection type laser device.

In a distributed reflection type semiconductor laser device manufactured by such a method, Fig. 3 (distributed reflection type laser current -
As shown in FIG. 2), an optical output of 30 mW and a differential quantum efficiency of 0.29 W/A were obtained during continuous oscillation at room temperature. In addition, the suppression ratio of adjacent modes is about 40 dB,
Stable single mode oscillation with a spectral linewidth of about 2 MHz was obtained.

[Example ■]

FIG. 4 is a cross-sectional view showing a schematic configuration of a main part of Example 2 of an anti-distribution type semiconductor laser manufactured by applying the present invention.

The difference between the distributed reflection type semiconductor laser of this embodiment (2) and the fabric reflection type semiconductor laser of this embodiment (2) is that, as shown in FIG.
and a distributed reflection region 103 having the same laminated structure as the distributed reflection region 102 having the inactive waveguide layer 3.

In an element having this structure, a narrow spectral linewidth can be achieved.

5A to 5F show an example of manufacturing the distributed reflection semiconductor laser shown in FIG. 4 by applying the manufacturing method of the present invention.
FIG.

The method for manufacturing the distributed reflection type semiconductor laser of this embodiment (2) is similar to the method of manufacturing the distributed reflection type semiconductor laser of this example (2), in which first, as shown in FIG. 5A, an n-type InP substrate is
An active waveguide layer made of InGaAsP (thickness 0.15 μm, bandgap wavelength 1.5
5 μm) 2. Protective layer made of InP (thickness 0.1 μm)
3A by metal organic vapor phase epitaxial growth (MOVPE)
They are sequentially laminated using a method.

Next, as shown in FIG. 5B, this n-type InP substrate 1
A 5in2 mask 3 is placed on the protective layer 3A as a predetermined area.
B is formed using, for example, a sputtering method and a photolithography method, and the active waveguide layer 2 and the protective layer 3 are formed using this 5in2 mask 3B and, for example, a chemical etching method.
Remove the unnecessary part of A and make it as shown in Figure 5B.
An island region (3B) having a length of about 200 μm and a width of about 40 μm is formed in the 1> direction.

Next, as shown in FIG. 5C, the SiO□ mask 3B
As a selective growth mask, an inactive waveguide layer (thickness 0.25 μm, band gap wavelength 1.3 μm) 3 made of non-doped InGaAsP is formed only in regions other than the island-like region.
is formed using the MOVPE method.

In this case, the pressure inside the reactor is set to about 50 T as a forming condition.
Because it is extremely low compared to orr and atmospheric pressure.

The raw material gas moves quickly on the surface of the n-type InP substrate, further promoting the effect of obtaining a flat growth surface.

Therefore, no growth occurs on the SiO□ mask 3B,
A flat growth surface as shown in FIG. 5C is obtained.

Next, after removing the 5un2 mask 3B with HF or the like, as shown in FIG. 5D, the protective layer 3A and the inactive waveguide layer 3 are removed.
A diffraction grating 10 with a pitch of about 2,400 and a depth of about 500 is formed over the entire surface using a two-bundle interference exposure method and a chemical etching method. in this case.

MOVP the upper surfaces of the protective layer 3A and the inactive waveguide layer 3.
It can be made flat by the E method.

Next, as shown in FIG. 5E, a cladding layer (thickness 2.0 μm) 4 made of p-type nP is formed on the diffraction grating 10.
Formed by VPE method or the like. In this case, since the cladding layer 4 uses the same InP as the protective layer 3A, the diffraction grating 10 formed on the protective layer 3A has virtually disappeared, as shown in FIG. 5F. It is the same as.

In the distributed reflection type semiconductor laser device manufactured in this way, as shown in Fig. 3 (a diagram showing the current-light output characteristics of the distributed reflection type laser), the optical output is 3 when continuous oscillation is performed at room temperature.
0 mW and a differential quantum efficiency of 0°29 W/A were obtained. Further, the suppression ratio of adjacent modes was about 40 dB, and stable single mode oscillation with a spectral line width of about 2 MH2 was obtained.

The present invention has been specifically explained above based on examples, but
It goes without saying that the present invention is not limited to the embodiments described above, and can be modified in various ways without departing from the spirit thereof.

〔Effect of the invention〕

As described above, according to the present invention, the active waveguide layer and the upper part can be formed with a uniform pitch by vapor phase epitaxial method by minimizing the mask area.

By optically matching and butt-coupling the inactive waveguide layer with a deep diffraction grating formed thereon, optical reflection scattering and electrical leakage at the coupling part are eliminated, resulting in high performance. A distributed reflection type semiconductor laser can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the schematic structure of Example 2 of a distributed reflection semiconductor laser manufactured by applying the present invention, and FIGS. 2A to 2F are distributed reflection semiconductor lasers shown in FIG. 1. Example I of manufacturing a laser by applying the manufacturing method of the present invention
FIG. 3 is a cross-sectional view of a main part of the manufacturing process showing the current-optical output characteristics of a distributed reflection laser manufactured by the method for manufacturing a distributed reflection semiconductor laser according to the present invention. FIG. 4 is an outline of the main part of Example H of a distributed reflection type semiconductor laser manufactured by applying the present invention. 8. FIGS. 5A to 5F are cross-sectional views showing the structure of FIG.
FIG. FIG. 6 is a diagram showing a mask pattern when manufacturing a conventional distributed reflection laser. In the figure, 1... n-type InP substrate, 2... InGaAg
P active waveguide layer, 3... n-type InGaAsP inactive waveguide layer, 3A... InP protective layer, 3B... Sun,
Mask, 4... p-type InP crat layer, 5... P-type InGaAsP cap layer, 6... p-type nP current blocking layer, 7... n-type InP current confinement layer, 8...
... n-type electrode, 9 ... P-type electrode, 10 ... diffraction grating, 11 ... coupling part between active waveguide layer and inactive waveguide layer,
101... Active region, 102.103... Distributed reflection region, 104... Phase adjustment region.

Claims (1)

[Claims] (1) An active waveguide layer on a semiconductor substrate having a first conductivity type, an inactive waveguide layer optically aligned and coupled to the active waveguide layer, and a thickness of the inactive waveguide layer. a first step of forming a laminated structure by sequentially laminating a protective layer having a thickness substantially equal to that of the active waveguide layer with a reduced thickness;
A second step of forming a predetermined island-like region on the laminated structure on the semiconductor substrate, removing the laminated structure other than the predetermined island-like region, and forming the laminated structure only in the predetermined island-like region. and a third step of forming an inactive waveguide layer having a thickness substantially equal to that of the layered structure and a substantially flat top surface only in a region other than the region where the layered structure is formed on the semiconductor substrate by vapor phase epitaxial growth. a fourth step of forming a diffraction grating on the upper surface of the protective layer and the inactive waveguide layer; and forming a cladding layer of a second conductivity type made of the same material as the protective layer on the upper surface of the diffraction grating. A method of manufacturing a distributed reflection semiconductor laser, comprising a fifth step of: