JPH0265192A - Manufacture of distributed feedback semiconductor laser - Google Patents

Abstract

PURPOSE:To partly vary the ratio of thicknesses of an active layer to a waveguide layer and to obtain a single wavelength oscillation with a low threshold value by employing the selective growth of an optical CVD crystal growing technique in a distributed feedback semiconductor laser. CONSTITUTION:A shielding mask 5 is mounted on a semiconductor substrate 1 formed with a diffraction grating thereby to form an optical guide 2 while radiating the part with a light. Then, a shielding mask 6 is employed to invert the part to be radiated with the light and the part to be shielded thereby to form an active layer 3. Thereafter, a different conductivity type clad layer 4 from the substrate 1 is formed. After these crystal growths are finished, a mesa stripe is formed, buried, grown to form electrodes, and its refractive index is varied on the way of the layer 2 to obtain a similar effect to that of a lambda/4 sift method. A distributed feedback semiconductor laser in which enables a single wavelength oscillation only at the Bragg's wavelength is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a distributed feedback semiconductor laser.

[Conventional technology]

FIG. 2 is a cross-sectional perspective view showing a part of the manufacturing process of a conventional distributed feedback semiconductor laser. In the figure, (1) is a semiconductor substrate on which a diffraction grating has been formed in advance. (2) is an optical waveguide layer, (3) is an active layer, and (4) is a cladding layer having a conductivity type different from that of the semiconductor substrate.

After forming each of the semiconductor layers described above, mesa stripes are formed in the light waveguide direction, but at this time, the stripe width is expanded only in the center of the laser element.

After passing through the above steps, a laser element is formed by forming a buried layer and forming electrodes (not shown).

Next, this DFB-LD (DisLribul, ad
The characteristics of Fe6dback-Laaer piode) will be explained.

In general, a DFB-LD has a diffraction grating formed in the optical waveguide, and uses this as a reflector to oscillate the laser, so the selectivity of the oscillation wavelength is better than that of an FP that uses the element end face as a resonator.
(￥abry Perrot) - Better than LD.

However, in a DFB-LD, simply forming a diffraction grating does not oscillate at the Bragg wavelength determined by the pitch of the diffraction grating, and instead has the same threshold gain at wavelengths equidistant from the Bragg wavelength. Since there are two oscillation modes, bimodal oscillation occurs. Therefore, in order to reduce the number of oscillation modes to one, the following manufacturing method has been considered.

(1) When forming a diffraction grating, the phase of the diffraction grating is shifted in the middle of the optical waveguide (λ/45ift method) (2) The refractive index of the optical waveguide is changed in the middle of the leading waveguide. d A method that has the same effect as the 5ift method.

This conventional example corresponds to the method (2) above.

(References; H, Kogelnik and CJ,
5hank, 'Coupled mode theor
y of distributed feedback
lasers,' J, Appl, Phys, vol.
, 43. pp 2327.1972) [Problems to be Solved by the Invention] Conventional distributed feedback semiconductor lasers were configured as one or more, so the current flowing through the wide part of the mesa stripe became a reactive current that did not contribute to oscillation. However, there was a problem in that it was difficult to reduce the threshold current.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to obtain a distributed feedback semiconductor laser that is capable of oscillating a single wavelength and of reducing the threshold value.

[Means to solve the problem]

The distributed feedback semiconductor laser according to the present invention is one in which the ratio of the thicknesses of the active layer and the waveguide layer is partially changed by using the selective growth property of the optical CVD crystal growth technique.

[Effect]

In the distributed feedback semiconductor laser of the present invention, by partially changing the ratio of the thickness of the active layer and the waveguide layer, the refractive index is partially changed, and an effect similar to that of the λ/45hifL method can be obtained. Single wavelength oscillation with low threshold.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
Figures (a) to (d) are cross-sectional views showing a part of the manufacturing process of a distributed feedback semiconductor laser. In Figure 1 (1)
-(4) are the same as those shown in the conventional example of FIG. 2, so their explanation will be omitted.

t5+ 1. t shielding mask l, +61 is shielding mass 'y 1 (511-shielding mask 2 with reversed brightness and darkness. +71 is irradiation light during crystal growth.

First, the semiconductor substrate (υ) on which the diffraction grating is formed (Fig. 1 (a)
)) One layer of optical waveguide (2) is formed while exposing a part of the semiconductor substrate (1) to light by placing a shielding mask 1 (5) thereon (v, Figure 1 (b)). Next, the active layer (3) is formed by using the shielding mask 2 (6) to invert the light-irradiated part and the shielded part (Fig. 1 (C)).
.

Thereafter, a cladding layer (4) having a conductivity type different from that of the semiconductor substrate (1) is formed (FIG. 1(d)).

After the above crystal growth is completed (not shown below), mesa stripe formation, buried growth, and electrode formation are performed.

Next, the operation will be explained. As shown in the conventional example, by changing the refractive index in the middle of the optical waveguide layer (2), the same effect as the λ/45ift method can be obtained. That is, a distributed feedback semiconductor laser capable of single-wavelength oscillation using only the Bragg wavelength can be obtained.

In addition, in the above embodiment; crystal growth was performed after forming the diffraction grating on the semiconductor substrate (11).
After forming an active layer (31) and an optical waveguide layer (2) thereon, a diffraction grating may be formed, and then a cladding B (4) may be formed.

〔Effect of the invention〕

As described above, according to the present invention, since the optical waveguide is formed using the optical CVD technique, a distributed feedback semiconductor laser with a low threshold value can be obtained.

[Brief explanation of the drawing]

FIGS. 1A to 1D are cross-sectional views showing part of the manufacturing process of a distributed feedback semiconductor laser according to an embodiment of the present invention, and FIG. 2 is a part of the manufacturing process of a conventional distributed feedback semiconductor laser. It is a cross-sectional perspective view showing (υ) a semiconductor substrate;
(3) is the active layer% (4) is the cladding layer, (5) is the shielding mask 1, [61 is the shielding mask 2, and (7) is the irradiation light. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] After forming a first semiconductor layer by optical CVD on a semiconductor substrate on which a diffraction grating is formed, using a mask having stripes perpendicular to the light waveguide direction to block light,
After forming a second semiconductor layer using photo-CVD in the same manner as above using a mask whose brightness and darkness are reversed from the above mask, and forming a third semiconductor layer having a conductivity type different from that of the semiconductor substrate over the entire surface. , for example, a method of manufacturing a distributed feedback semiconductor laser characterized by forming mesa stripes in the light waveguide direction and performing buried growth.