JPS58114476A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain high coupling efficiency of a semiconductor laser by forming a tapered region by varying the width without varying the thickness of an active layer. CONSTITUTION:An n type Ga1-uInuAsvP1-v waveguide 12, non-added GaxIn1-x AsyP1-y active layer 13, a p type InP clad layer 14 and a buried layer 15, and a p type GaInAsP cap layer 16 are superposed on an n type InP substrate 11, x>u, y>v are established, the other surface is formed by the coupling side, and electrodes 16, 17 are attached. A region A is formed of the active layer 13 of the prescribed width and the waveguide 12 with intrinsic light distribution determined by the refractive index distribution, but in case of propagation, since the active layer width is uniformly reduced in the tapered region B, the light distribution is not almost scattered, but is propagated in the region C, and the regions A and C are coupled in high efficiency. On the contrary, in case of reverse propagation, similar operation occurs. When the width of the waveguide 12 is approx. 2mum, the length of the region B is approx. 50mum and the end is less than 0.5mum the advantages are remarkable. This configuration can be formed with good reproducibility in the planar process steps, and a resonator can be made available by forming rugged surface 19 on the region A or C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser, and in particular provides a structure that provides high coupling efficiency between an active layer and a waveguide layer, which are essential for integrated lasers.

In order to integrate multiple optical devices such as semiconductor lasers on the same substrate, it is essential to have a structure in which a low-loss waveguide is coupled to a photoactive device. In order to operate at high performance, it is important that the coupling between the active layer and the waveguide is sufficiently large. Until now, one of the structures aimed at achieving high coupling between the active layer and the waveguide layer is the taper coupling shown in FIG. 1 for the purpose of integrated lasers such as Tono. In the figure, 1 is a semiconductor substrate such as 1nP, 2
3 is a waveguide layer, 3 is an active layer, 4 is a cladding layer, and 6 is a cap layer. Light is generated in region A and coupled into region C, where the light is generated in region A and coupled into region C.

In region B between 6 and 6, there is a tapered region in which the layer thickness of the active layer changes uniformly. Figure 2 shows ■-Ilail in Figure 1.
As shown in the i-plane and light distribution, in order to prevent scattering in the light distribution in region A, the light distribution in the tapered region is uniformly changed gradually to match the light distribution in region C to achieve high coupling. It has the advantage of achieving high coupling efficiency, usually around 90%.
However, the above-mentioned Taper bond groove structure requires gradual changes in the thickness of the active layer 3, and although it is often fabricated by liquid phase growth, special ingenuity is required for the equipment in order to fabricate it, and There was a problem with the reproducibility of the manufactured taper shape. That is, as shown in FIG. 3, the method for manufacturing the tapered region by liquid phase growth is such that when growing the active layer 3 on the waveguide layer 2, the melt 7 in the graphite boat 9 flows out from under the shielding plate 8. It takes advantage of growth. Therefore, melt 7
The set height of the shielding plate 8 must be adjusted according to the temperature and viscosity of the shielding plate 8, and this work is difficult, resulting in problems with the reproducibility of the taper shape. Furthermore, as can be seen from FIG. 3, since the atmospheres for growing the tapered region B and the region A are greatly different, there is a drawback that the respective compositions are different.

The present invention improves the above-mentioned drawbacks of the prior art, and
The object of the present invention is to provide a semiconductor laser having a structure in which a tapered region is formed by changing the width of the active layer instead of changing the thickness of the active layer, and which can obtain high coupling efficiency and can be manufactured by a planar process.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

A perspective view of an embodiment of the present invention using GaInAsP crystal (a) K, 17) PJ-IVa cross-sectional view (b) K, i fc, top view when the stripe portion is exposed are shown in FIG. 4(e). In the figure, 11 is n-type InP Motoya, 12 is n-type Ghu n1-u
A waveguide layer consisting of AsvPl-v, 13 is an undoped G
an active layer consisting of axIn, -XAsyPl-y, 14 a p-type InP layer, 15 a p-type InP buried layer,
16 is a cap layer made of p-type GaInAsP;
The waveguide layer 12 and the active layer 13 have a relationship of x)u and y)y. Although the other end is not clearly shown in the figure, it may have the same configuration as shown or a cleavage plane, and is determined depending on what kind of elements are to be coupled. These semiconductor layers can be formed by liquid phase epitaxial method, vapor phase epitaxial method, bimolecular beam epitaxial method, or the like. 17 and 18 are p-side and n-side electrodes, respectively. Here, region A is a striped active layer 13 with a constant width.
and a waveguide layer 12, region C consists only of the striped waveguide 12, and region B is a tapered region in which the width of the active layer 13 changes continuously, which is a feature of the present invention.

The light generated in region A has a unique light distribution determined by the refractive index distribution of region A, but when the light propagates in two directions, the width of the active layer uniformly decreases in region B. The distribution is uniformly deformed without being scattered all the time, and the area C
At the boundary between region B and region B, the deformed light distribution propagates within region C in accordance with the light distribution specific to region C. That is, since the scattering of light in the tapered region B is extremely small, light can be coupled from the region A to the region C with high efficiency. Although an example in which light propagates in two directions has been described above, the same applies to the case in which light propagates in the -2 direction, that is, from region C to region A.

Figure 5 shows how light propagates. FIG. 5(b) is an enlarged view of the optical coupling part, where V-1, V-n, V-m,
%L-IV.

■-■ indicates the cut plane, and the cross sections (1), (II), (to) l (V) corresponding to each cut plane are shown in Fig. 5(a).
+ (capital) and light distribution are shown. The light confinement effect depends on the refractive index and cross-sectional area of the layer. The refractive index of the active layer 13 is greater than the refractive index of the waveguide layer 12. Therefore, at the position of cross section V-1, light is mainly confined within the active layer 13, but as the cross-sectional area of the active layer 13 becomes smaller, the amount of light confined within the waveguide layer 12 decreases. In many positions of the cross section (V-V), the light distribution is unique to region C.

In addition, as a specific example of the shape and size of the tapered region B in FIG. 4, when the waveguide layer 12 is about 2 μm long and the length of the tapered region B is about 50 μm, the tip of the tapered portion is about 0.5 μm long.
The effect of the present invention is significant below m.

An example of the manufacturing process of the embodiment shown in FIG. 4 is shown in FIG.

The wafer is fabricated by two rounds of crystal growth. First, the first
By the second growth, a waveguide layer 12 is formed on the InP substrate 11,
Active layer 13. The InP cladding layer 14 is sequentially grown [FIG. 6(a)]. Next, the cladding layer 14 and the active layer 13 are removed by etching so that tapered wedge-shaped stripes remain [FIG. 6(b)]. Furthermore, a linear stripe mask is applied again so as to overlap the wedge-shaped stripes, and etching is performed up to the InP substrate 1 [FIG. 6(C)]. Next, the tapered stripes are completely filled with InP by the second moon growth [FIG. 6(d)]. In this way, active layer 1
Compared to tapering the active layer thickness as shown in FIG. ,
Its shape can also be produced with good reproducibility.

Note that the resonator may be a DFB (distributed feedback) type in which periodic unevenness 19 is provided in region A shown in FIG. Unevenness 1
This can be realized by using an I) BR (distributed reflection) type in which 9 is provided.

The above embodiment has been shown using a structure in which the active layer 13 and the waveguide layer 12 are directly bonded, but the active layer 13 and the waveguide layer 12 are
It can also be applied to a structure in which a low refractive index layer such as InP is interposed. Furthermore, the present invention is also applicable to an embodiment using GaInAsP/InP crystals (although this is shown above, it is also applicable to AlGaAs-based mixed crystals, etc.).

As described above in detail, according to the present invention, a tapered coupling structure with a high coupling coefficient can be fabricated with good reproducibility through a simple planar process, and therefore a low threshold and highly efficient integrated laser can be realized. You can expect it.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a conventional tapered coupling structure in which the active layer thickness changes, FIG. 2 is a cross-sectional view taken along line II-11a in FIG. 1 and shows how the light distribution changes. 4(a) is a perspective view showing the embodiment of the present invention, FIG. 4(b) is a cross-sectional view for explaining the method of forming the example, FIG.
V-IVa sectional view, FIG. 4(c) is the ■--V in FIG. 4(a)
5 (a) (b) is a cross-sectional view and a perspective view showing the propagation of light in the device of the present invention, FIG.
(a), (b), (c), and (d) are perspective views showing the manufacturing process of an embodiment of the present invention, and FIG. 7 is an embodiment in which the present invention is applied to a DFB and DBR structure. 1- InP substrate, 2 =-GauInl-uAsvP
l-v waveguide layer, 3...Gax In H-xAs
y P 1-y active layer, 4 =-InP cladding layer,
5... InP buried layer, 6... GaInAsP canog layer, 7, 8... electrode, 9... periodic unevenness,
11...n-type InP substrate, 12-n-type GauIn1-
uAsvPl-, waveguide layer, 13...GaxIn
1-XA5yP 1-y active layer, 14-p-type InP cladding layer, 15... p-type InP buried layer, 16...
p-type GaInAsP cap layer, 17... p-side electrode,
18...n-side electrode. Patent Applicant International Telegraph and Telephone Corporation Agent Oita 1 person from outside the university 1 Seki 2 Sen 3 Kuni 4 1-2 ■6 -A--←BCmonutsu) (0) (b) Figure 6 Figure 7

Claims (1)

[Claims] On a semiconductor substrate, a first semiconductor layer, a second semiconductor layer having a smaller forbidden band width than the first semiconductor layer and serving as a waveguide, and the first semiconductor layer. a third semiconductor layer having a smaller forbidden band width than the second semiconductor layer and serving as an active layer;
A fourth semiconductor layer having a forbidden band width comparable to that of the first semiconductor layer is sequentially stacked, and a portion of the active layer is removed. Second. Third. Region A consisting of a fourth semiconductor layer; Second. In a semiconductor laser configured to oscillate by propagating light across both region C comprising a fourth semiconductor layer, or to oscillate only in region A and transmitting the oscillated light to region C, A semiconductor laser characterized by having a region B between the regions A and C, the width of which is continuously reduced in a direction parallel to the bonding surface of the active layer.