JPS61137385A - Vertical mode control semiconductor laser - Google Patents

Abstract

PURPOSE:To facilitate the manufacture by holding a zone of polycrystals having different refractive indexes in a resonator to form a vertical mode control semiconductor laser. CONSTITUTION:An SiO2 stripe 12 of the prescribed size is formed by a photolithography at a suitable intermediate position of an end resonator length on a substrate 10. An N type InP buffer layer 11 and a current narrowing reverse junction 4B are grown thereon. A groove is formed by chemical etching in a direction perpendicular to the stripe 12 by a photolithography, buried and grown in the groove to grown an N type InP N type clad layer 2, an undoped InGaAsP active region 1, a P type InP P type cap layer 5 are grown. An end resonator is formed by cleavage, electrodes 6, 7 are attached to obtain a vertical control semiconductor laser of internal reflection interference type.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a light source for optical communication, particularly to a longitudinal mode controlled semiconductor laser for broadband transmission. More specifically, the present invention relates to improvements in internal reflection interference longitudinal mode control type semiconductor lasers.

BACKGROUND OF THE INVENTION In recent years, with the improvement of optical communication technology, efforts have been made to widen the transmission band. However, conventional semiconductor lasers do not necessarily have a single longitudinal mode, and it is difficult to say that they have sufficient performance for this purpose.

For this purpose, various structures have been studied, such as distributed feedback type (DFB), distributed Bragg reflection type (DBR), and cleavage-coupled resonator type (C5). It has been demonstrated that semiconductor lasers using these structures can have extremely good characteristics if carefully manufactured. However, its creation is actually not easy. That is, D.F.
B. In DBH, there are difficulties in creating a fine diffraction grating on a semiconductor wafer using large equipment and in a quiet environment, and then growing crystals on this without damaging it. , C3 also required a sophisticated technique of assembling two semiconductor laser chips with their active regions, each having a cross section only a few μm wide, facing each other. For this reason, various other attempts have been made to obtain single-longitudinal mode oscillation.

Internal reflection interference (IRI) semiconductor laser is a Mod
e InGaAsP/ InP Internal-
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An example of its structural diagram is shown in FIG. 4, and its operating principle will be briefly explained according to the drawing. FIG. 4a is a diagram showing an end face of an IRI semiconductor laser, which is no different from a conventional semiconductor laser. 41 is an active region, 42 is an n-type cladding, 43 is a p-type cladding, 44 is a reverse junction for current confinement, 45
is a cap layer, 410 is a substrate, 411 is a buffer layer, 4θ is a p-type electrode, and 47 is an n-type electrode. The feature of the IRI semiconductor laser is the cross-sectional view including the active region from the lateral direction (Figure b)
is shown. 48 is a dividing portion that divides the active region 41 into two. The section is made of a material with a slightly different refractive index relative to the active region and provides an internally reflective surface 49 to the active region 41 . By energizing the electrodes 46 and 47, an oscillation mode with a larger wavelength period is superimposed on the normal oscillation mode due to end face reflection as a result of internal reflection interference caused by 49. Therefore, the selectivity of the oscillation dominant wavelength is increased,
Oscillation with high longitudinal mode unity can be obtained.

Problems to be Solved by the Invention However, in conventional IRI semiconductor lasers, the divisions are formed by chemical etching, and therefore, although it is relatively easy to create them, it is not necessarily completely easy. Furthermore, it is difficult to make the angle of the internal reflection surface 49 perpendicular to the active region 41 in order to utilize the crystal orientation selectivity of etching.

It is an object of the present invention to solve the above-mentioned problems of the prior art and to provide an IRI type longitudinal mode control semiconductor laser having a structure that is easier to manufacture.

Means for Solving the Problems The present invention provides a longitudinal mode control type semiconductor laser which has sectioned sections with different refractive indexes within a resonator and is characterized in that the sectioned sections are polycrystalline. This aims to achieve the above objectives.

Operation: This makes it possible to more easily obtain an IRI type longitudinal mode control type semiconductor laser having a good segmented portion.

EXAMPLE A first example of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a longitudinal mode controlled semiconductor laser according to an embodiment of the present invention, including a cavity end face and an active region viewed from the lateral direction. Furthermore, FIG. 2 shows the substrate used for growth (inside the growth wafer) in producing the longitudinal mode control type semiconductor laser in the same embodiment.

Only the portion corresponding to one element is shown. 1
0 is a substrate, and 12 is a stripe of an insulating film arranged at an appropriate position on this substrate. Furthermore, in this embodiment, a semiconductor laser is manufactured using a method similar to that used for manufacturing a normal semiconductor laser. However, in this embodiment, the MOCVD method is used as the crystal growth method on the substrate. This is because, unlike the commonly used LPE method, the 1M0CVD method has the characteristic that polycrystals grow on the insulating film.

The method for manufacturing the longitudinal mode controlled semiconductor laser of this example is as follows.

A film with a width of 0.7 μm is formed on the substrate 10 at an appropriate position approximately in the middle of the end facet resonator length using photolithography.

8102 stripes with a thickness of 0.1 μm are formed. On top of this is an n-type InP buffer layer 11. A p-type InP layer 4A and an n-type InP layer 4B for forming a reverse junction 4 for current confinement are grown. At this time, the portions of these layers grown on the S102 stripes 12 are polycrystalline. Now, Ho I-
SiO using IJ lithography. A groove is formed by chemical etching in a direction perpendicular to the stripe 12, and an n-type cladding 2. of n-type InP is grown by filling it in the groove. An active region 1 of undoped InGaAsP and a p-type cladding 3 of p-type InP are grown, and then p-type InGaAsP is grown.
Grow a cap layer 6 of P 2 . At this time, portions 2, 1, and 3.5 corresponding to the portions above the SiO□ stripes 12 inherit the properties of the underlying layer and grow into polycrystals (shown by the hatched area in FIG. 1). An end facet resonator was formed by cleavage, and an electrode 6°7 was attached to obtain the IRT type longitudinal mode controlled semiconductor laser shown in FIG. Here, the polycrystalline portion of the active region is located in the end facet resonator and constitutes a section 8.

In the case of the same crystal, the difference in refractive index between single crystal and polycrystal is minute, and polycrystal has low transmittance.However, the IRI type semiconductor laser obtained by the above method has a threshold current of 1 Stable single-longitudinal mode oscillation of 1.54 μm was exhibited at .2 to 2.3 times.

This is presumed to be due to the fact that the shape of the internal reflection surface 9 in this example is vertical and relatively good, and that the width of the partitioned portion is made as small as possible.

Next, a second embodiment of the present invention will be described.

FIG. 3 is a cross-sectional view of the longitudinal mode control type semiconductor laser in the second embodiment, including the active region, viewed from the lateral direction.

In this embodiment, instead of the insulating film stripes of Embodiment 1, weak scratches 312 are made by scratching at the same position.
We tried a similar manufacturing method using a board with . The IRI type semiconductor laser of this example has a threshold current of 1.5 to 2.
．． It exhibited stable single-longitudinal mode oscillation of 1.46 μm at 1× magnification.

Note that all of the above embodiments are based on semiconductor lasers with a grooved substrate (C3) structure;
Almost the same effect can be obtained in experiments using semiconductor lasers with this structure. Further, any possible growth method other than the MOCVD method may be used. In order to form the polycrystalline section, in addition to the insulating film stripes shown in FIG.
02 or a polycrystalline layer may be used as the base. Needless to say, shapes other than stripes are also acceptable.

Effect of the invention By making the internal reflective surface a polycrystalline structure.

- facilitates its manufacture;

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a longitudinal mode controlled semiconductor laser according to a first embodiment of the present invention, including a cavity end face and an active region viewed from the lateral direction. 3 is a sectional view including the active region seen from the lateral direction in the second embodiment of the present invention; FIG. 4 is a resonator end face of a conventional LRI longitudinal mode control semiconductor laser; and FIG. FIG. 3 is a cross-sectional view including an active region when viewed from the lateral direction. 1... Active region, 2... N-type cladding, 3... P-type cladding, 8... Division section, 9... Internal reflective surface, 10... Substrate, 12... Insulating film stripe, 312...
...Scratch. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure 4

Claims (3)

[Claims] (1) Having sections with different refractive indexes in the resonator, and
A longitudinal mode control type semiconductor laser characterized in that this section is polycrystalline. (2) A longitudinal mode control type semiconductor laser according to claim 1, wherein a segmented portion is formed on the surface of the substrate with an insulating film interposed therebetween. (3) A longitudinal mode control type semiconductor laser according to claim 1, characterized in that a segmented portion is formed on a scratch provided on the surface of the substrate.