JPS5880888A - Integrated semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain an integrated semiconductor laser which can be operated with a low threshold current and which can be readily manufactured by slowly forming a tapered shape in the thickness of a layer of a laser waveguide. CONSTITUTION:An active layer 1 and an output waveguide layer 2 having refractive index smaller than that of the layer 1 and larger than those of the first and second clad layers 3, 4 has a laser waveguide structure which is interposed between the first and second layers 3 and 4, and further has the first and second output regions 6, 7 removed with the layer 1 and the active region 5 which has the remaining layer 1. The thickness of the layer 2 in the region 4 is not uniform, but is the thinnest at the center, and increases in the thickness gradually toward the regions 6, 7, and increases larger in the thickness than the active layer in the vicinity of the boundary between the region 5 and the regions 6, 7. The light power distributions 8, 9, 10 increases in the distribution rate toward the layer 1, the power distribution of the boundary between the regions 5 and 7 is displaced to the side of the layer 2, approaches in shape to the power distribution in the region 7, the light coupling amount of the region 5 and the regions 6, 7 can be increased, thereby remarkably reducing the oscillating threshold current.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is one of the first optical integrated circuits that is easy to manufacture! Regarding the semiconductor laser that is the element.

Conventionally, there are LOC (Large, Optical, Cavity) II and integrated dual waveguide models as typical examples of medium conductors for optical-optical integrated circuits. 2 above
In both types of lasers, the laser waveguide consists of two layers: an active layer and an equal wave path for output], and further has two regions: an output region where part of the active layer is removed by etching, and an active region where the active layer is left. The layer thicknesses of the active layer and the output and wave path layers are uniform throughout. For this reason, in order to create a structure in which the amount of light coupling between the active region and the output region is reasonable in n,Loc@ semiconductor lasers, the active layer thickness must be made sufficiently thinner than the output waveguide layer thickness. If this is done, the ratio (distribution ratio) of the electric field to the active layer in the active region will be small, resulting in p1 oscillation, and the iI/% value current will increase. vice versa.

The structure greatly increases the distribution ratio of the electric field to the active layer in the active region, and the active layer thickness must be approximately the same or greater than the output waveguide layer thickness.

Is this the light of the nine active areas and output area mentioned earlier? The amount of coupling is reduced, oscillation is made, and the strong cage current is increased.

The details must be based on the electromagnetic field distribution taking into account the refractive index of the active layer and the output waveguide, but to put it simply, it is necessary to simultaneously increase the distribution ratio of the electric field to the active layer and the coupling between the active region and the output region. The inability to do so was a major drawback of the LOC structure. On the other hand, since integrated dual waveguide lasers must be manufactured so that the active layer and the output waveguide layer form a coupling waveguide, a high degree of controllability is required in crystal growth.

SUMMARY OF THE INVENTION An object of the present invention is to provide an integrated conductor laser that operates at a low threshold current and is easy to manufacture.

According to the present invention, the waveguide structure has a waveguide structure in which an active layer and an output waveguide layer having a smaller refractive index than the active layer are further sandwiched between cladding layers having a smaller refractive index, and the active layer is removed therein. In the active region, the output waveguide layer extends from several tens of nanometers to several tens of nanometers from the boundary between the output region and the active region toward the center of the active region.
An integrated semiconductor laser having a structure that becomes gradually thinner over a length of 0.00 cm is obtained.

In the integrated semiconductor laser of the present invention, the electric field in the active region is made to have a high distribution ratio of light to the active layer, and the output waveguide layer thickness is made larger than the active layer thickness in the output region and in the vicinity of the active region. ,
The proportion of the electric field in the output waveguide layer can be increased. This allows low threshold current operation. Furthermore, since the active layer and the output waveguide layer are adjacent to each other, fabrication is easy because high controllability of crystal growth is not required as in the case of an integrated double waveguide.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a cross-sectional view in the laser resonator direction of one embodiment of the present invention. In this embodiment, the active layer l has a smaller refractive index than the active layer l, and The two layers of the output-wave path layer 2 having a higher refractive index than the second cladding layer 3.4 are the first cladding layer 3.4. It has a nine laser waveguide structure sandwiched between the second cladding layers 3 and 4, and the active layer l adjacent to the output waveguide layer 2 has been removed. 2 output regions 6, 7 and the active layer 1 are left with nine active regions 51''.The output waveguide layer 2 in the active region 5
The layer thickness is not uniform, being thinnest in the center and gradually thickening toward the first and second output regions 6, 7, and the active region 5 and the first and second output regions 6, 7. It has a structure that is larger than near the boundary of the 20th output region 6.7. This also includes a case where the output waveguide layer is partially uniform in the center of the active region 5. 9.10.11a [The power distribution of light at each position in] In the power distribution of 9, the distribution ratio to the active layer 1 is high, and the power distribution of the boundary between the active region 5 and the output region 7 of 10 is as follows. Output waveguide layer 2-
, the shape becomes close to the power distribution in output region 7,
The active region 5 and the first. The amount of light coupled to the second output region 6°7 can also be increased, and the oscillating colored line current can be reduced to a large extent.

FIG. 2 is a sectional view for explaining the manufacturing process V& of the semiconductor laser shown in FIG. As shown in Figure 2-), (10
G) A quaternary layer 21t of fllLl made of GaInAsP, which has a band gap larger than that of the active layer composition and smaller than InP, is formed on the laP substrate 20 by normal liquid phase growth.
O, 5-1.0 μm flat growth. The length of the active region is 2 as shown in FIG. 2(b)K.
Etching is carried out by ion etching or reverse sputtering using an etching mask 30 so that the etching thickness is 00 μm" - 400 mK. At this time, an appropriate space is placed between the mask and the wafer so that the etching shape is a gentle chi/<- shape. Create a space.The tapered quench obtained by the above process is etched to remove the serious defects introduced during etching with bromine methanol, and then the second liquid phase growth process is used for output, etc. Ga with the same composition as the wave layer (corresponding to a quaternary layer with 2x < ml)
An InMusP quaternary layer of about 0.1 μm is laminated thereon,
Immediately, an active layer 22 and an InP cladding layer 23 are successively grown to produce the semiconductor laser structure shown in FIG. 2(C). Furthermore, as shown in FIG. 2(d), the upper part of the p-output waveguide layer 21, including the active layer 22, where the layer thickness has increased due to cul-etching, is removed, leaving no trace on the surface. 824
and form an electrode using a normal electrode forming method). The semiconductor fabricated as described above is a laser waveguide.
〇-The thickness is not uniform and the shape is gently tapered) The scattering loss is small, and the electric field strength of the active region to the active region where the current is injected and the electric field strength to the output waveguide in the output region are small. Since the coupling of light can be increased, a low threshold current is possible. Furthermore, since the active layer and the output waveguide layer are adjacent to each other in the LOCfi structure, the formation of the active layer and the waveguide layer does not require high controllability and is easy to manufacture.

The present invention can be modified in various ways in addition to the preferred embodiments described above. The semiconductor material line is not limited to InGaAs1' series (other materials such as GaAJLAs series may also be used).

It is also possible to form a so-called distributed feedback laser by forming periodic irregularities on the output waveguide in the output region. Further, the number of output areas may be one.

[Brief explanation of the drawing]

FIG. 1 shows an implementation of the semiconductor laser of the present invention #if
fi1m, and FIGS. 2(a) to 2(d) are process cross-sectional views showing a method of manufacturing the semiconductor laser shown in FIG. 1. l, 22... Active layer, 2, 21... Output waveguide 111, 3.4... 1st. Second cladding layer, 5...Active region, 6.7...
・Output region, 8, 9.10... Light power distribution % at the position of the pot in the figure 20... InP substrate, 23... InP cladding layer, 24.・・・・・・
- Insulating film, 30... Etching mask. Procedural amendment (voluntary) Showa V “Ki Day 1, Indication of the incident 1986 Fortress permission application No. 1 eg
o number 2, name of m1ll integrated semiconductor laser 3, person making the amendment Relationship with the case Applicant 5-33-1-4 Shiba, Minato-ku, Tokyo, attorney's specification or invention details #I*WRIIJ Column. 6 Contents of amendment

Claims (1)

[Claims] an active layer and the active layer adjacent to the active layer; a waveguide structure including an output waveguide layer with a small refractive index and a rad layer with a refractive index even smaller than the two layers sandwiching both sides of the two layers; and has two regions, an output region from which the active layer is removed and an active region from which the active layer remains, in which the output waveguide layer thickness within the active region is approximately equal to that of the active region. An integrated semiconductor laser characterized by a gradual decrease toward the center.