JPH02237189A - Manufacture of single wavelength laser - Google Patents

Abstract

PURPOSE:To improve the yield by forming an active layer periodically in the direction of a laser resonator and then forming crystals having approximately the same equivalent refractive index as the active layer and no gain in the parts other than the active layer by crystal growth after then. CONSTITUTION:A first clad layer 2 of n-type InP, an InGaAsP active layer 3, and a second clad layer 4 of P-type InP are formed in that order on an n-type InP substrate 1. A dielectric thin film is formed and dielectric masks 5 of a corresponding cycle to the excitation wavelength of a laser are formed by photoengraving and etched to form periodic etching grooves 6 reaching the clad layer 2. Semi-insulating InGaAsP layers 7 having approximately the same equivalent refractive index as the InGaAsP active layer 3 are formed in the etching grooves 6, the dielectric masks 5 are removed, and p-type InP third clad layer 8 and then a p-type InGaAsP contact layer 9 are grown. Thereby failures in forming diffraction gratings are decreased to obtain a high yield.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a manufacturing method for improving the manufacturing yield of single wavelength lasers.

[Conventional technology]

FIG. 2 shows a cross-sectional view of a conventional single wavelength laser in the cavity direction. In the figure, (1) is an n-type rnP substrate, cgi
+ indicates the diffraction grating formed on the InP substrate (1), (31
) is the one-wavelength phase shift part of the diffraction grating +21) formed in the center of the resonator, αυ is the n-type rnGaAsP waveguide layer (bandgap Eg) s (8) is the rnGaAsP active layer (bandgap, vertical <"gL (4) is p-type In
The P cladding layer (6) is a p-type InGaAsP contact layer. FIG. 3 shows a cross-sectional view of the process of forming a one-wavelength phase shift type diffraction grating. In the figure, %■ indicates negative resist;
(2) is the intermediate layer ObC, U is the first positive resist, (G) is the second positive resist, and (G) is PVAp.

Next, a conventional laser manufacturing process will be explained. First, a diffraction grating having a one-wavelength position shift part (31) at the center of the laser is formed on an n-type 1nP substrate (1) by using an interference exposure method. The process for forming this diffraction grating (21l) is complicated. The method for forming this diffraction grating will be explained with reference to FIG.

FIG. 3 (first positive resist of intermediate 1@oba film of negative resist on Al-N type RNP substrate (1)) t241 is formed.

FIG. 3 (bl) A part of the first positive resist 24J is removed using a normal photolithography.

Figure 3 (01-1st positive resist} Negative resist of oF:3c film in nitric acid solution using C!41 pattern}
Etch E.

Fig. 3 fdl-first positive register} (After removing 241,
Second positive resist ■, PVA! Form I (261).

Figure 3 (, 3) - After performing interference exposure, development and rinsing are performed, and the pattern formed by the negative resist and the second positive resist of the PVA film and the intermediate layer OHO film is used on the substrate (1). - Etching.

Thereafter, the second positive resist track of the negative resist is removed to form a diffraction grating c2υ having a one-wavelength phase shift portion (31) in the center.

Next, n is placed on the diffraction grating +211 formed in this way.
InGaAsP waveguide layer αl, rnGaAsP active layer (81), p-type InP cladding layer (4), p-type I
A laser structure is formed by sequentially growing nGaAsP contact layers (6).

A one-wavelength phase-shift distributed feedback laser manufactured through such a process is theoretically capable of single-wavelength oscillation with a yield of 100%.

[Problem to be solved by the invention]

The conventional manufacturing method for single wavelength lasers is configured as described above, so in order to form a distributed feedback laser that oscillates at a single wavelength with 100% yield, it is necessary to shift the phase by one wavelength in the center of the laser cavity. It is necessary to form a diffraction grating on the substrate, which requires the above-mentioned complicated process, resulting in a poor yield for forming the diffraction grating or a non-uniform diffraction grating. There was a problem that the manufacturing yield was low.

The present invention has been made to solve the above-mentioned problems, and aims to provide a manufacturing method that improves the manufacturing yield υ of single wavelength lasers.

[Means to solve the problem]

The method for manufacturing a single wavelength laser according to the present invention is to form an active layer periodically in the direction of the laser cavity, and through subsequent crystal growth, the portions other than the active layer have an equivalent refractive index that is approximately equal to that of the active layer, and a gain can be achieved. It is a crystal that does not have .

[Effect]

In the method for manufacturing a single wavelength laser according to the present invention, the formation of a periodic active layer in the direction of the cavity that plays the role of a diffraction grating can be performed by ordinary interference exposure and etching, so the process of forming the diffraction grating is not complicated. First, the manufacturing yield of single wavelength lasers is improved.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a cross-sectional view in the direction of the laser cavity, showing the steps of the method for manufacturing a single wavelength laser according to the present invention. In the figure, (1) is the n-type rnP first cladding layer, (8) is the In
GaAsP active layer, (4) is P-type InP second cladding layer, (6) is a dielectric mask, (6) is a periodic etching groove, (γ) is an equivalent refraction that is almost equal to that of the InGaAsP active layer (8) Semi-insulating [nGaAsP i@
, (8) is a p-type fnP third cladding layer, and (9) is a p-type InGaAsP contact layer.

First, as shown in Figure 1 (al), an n-type 1nP substrate (1)
As the first crystal growth, an n-type TnP first cladding layer f2), l:nGaAsP active layer 181*P is formed on top.
A second cladding layer (4) of InP type is sequentially formed. Here, the n-type 1oP first cladding layer (2) is an InP substrate (
It also serves as a buffer layer to reduce the effects of 1). This layer may be omitted in some cases. The crystal lengthening here is done in order to improve the controllability of the periodic active layer (8) formation in the next step! It is more effective to use a method with good layer thickness controllability, such as ,IIOcV]).

Next, SiOz is deposited on the wafer that has undergone the first crystal growth.
Alternatively, a dielectric thin film such as SiN is formed, photolithography is performed using normal interference exposure, and the dielectric thin film is etched.
6) Form. Next, as shown in Figure 1, etching is performed using a dielectric mask (6) to
Periodic etching grooves (6) are formed that bend down to the first cladding layer (2). Next, as shown in Figure 1 tc), 2
Perform the second crystal growth and create periodic etched grooves (6)
InOaAsP active layer (8) and #1! 'Z, semi-absolute, permissive InGaA, SP layer with equal equivalent refractive index (7)
form. This semi-insulating TnGaASP III (
7) is thicker than active layer (8), so active layer < s
) is composed of a crystal with a wider dogap than . The p-type InP third cladding layer (8) is formed by crystal growth of
A p-type [nGaAsP contact layer (9) is sequentially grown to form a laser structure. After that, an electrode stripe structure or buried structure is formed, and the p-side, ! An electrode is formed on the first side.

When a voltage is applied in the forward direction and a current is caused to flow in the laser manufactured by such a process, the current flows through the periodically formed InGaAsP active layer (8) in the direction of the cavity, and the current flow in the direction of the cavity. A periodic distribution is created.

In this laser, the part where the current flows is the gain region, so
It has periodic gain fluctuations in the cavity direction, making it a gain-coupled distributed feedback laser. As a result, single wavelength oscillation is theoretically possible with a yield of 100%.

In the laser manufacturing method of the present invention, the diffraction grating formation process, which is the most important process for distributed feedback lasers, is not complicated, so there are fewer failures in diffraction grating formation than in the conventional manufacturing method K, and the uniformity of the diffraction grating is improved. good.

In the above embodiment, the semi-insulating InGaAsP layer αυ was used as the crystal grown in the periodic etching grooves (6), but this may be n-type or p-type 1nGaAsP.
It can also be a layer. Further, any other material may be used as long as it has a lattice constant that matches that of InP, has an equivalent refractive index substantially equal to that of the active layer (8), and has a wider band gap than the active layer (8).

Furthermore, although the method for manufacturing an InP-based laser has been described in the above embodiment, other material systems such as GaAs may also be used, and the same effects as in the above embodiment can be achieved.

〔Effect of the invention〕

As described above, according to the present invention, a gain-coupled distributed feedback laser is constructed by forming a periodic active layer in the direction of the laser resonator using the ordinary interference exposure method. This has the effect of making it possible to manufacture wavelength lasers.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a laser in the cavity direction showing the manufacturing process according to an embodiment of the present invention, Fig. 2 is a cross-sectional view of a conventional single wavelength laser in the cavity direction, and Fig. 3 is a one-wavelength phase shift diagram. FIG. 3 is a cross-sectional view showing a step of forming a shaped diffraction grating. In the figure, (1) is an n-type InP substrate, (2) is an n-type I
nP first cladding layer, (8) InGaAsP active layer, (4) P-type InP second cladding layer, (5) dielectric mask, (6) periodic etching groove, (γ) A semi-insulating InGaAsP layer, (8) a P-type InP third cladding layer, and (9) a P-type InGaAsP contact layer. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Figure 1

Claims (1)

[Claims] In a distributed feedback semiconductor laser having an active layer periodically formed on a semiconductor substrate in the direction of the laser cavity, there are two steps: forming an active layer and a cladding layer on the semiconductor substrate, and forming the active layer along the direction of the cavity. A process of forming periodic grooves that reach the bottom, a process of forming in the grooves a semiconductor layer that has an equivalent refractive index almost equal to that of the active layer and a wider band gap than the active layer, and after these steps, the entire wafer A method of manufacturing a single wavelength laser, the method comprising: forming a cladding layer;