JPS6320389B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an InP-based semiconductor laser device that facilitates alignment between a laser oscillation region and an optical fiber that receives light emitted from the laser oscillation region, and a method for manufacturing the same.

When a semiconductor laser is used for optical communication, it must be aligned with an optical fiber with high precision, but alignment when using a single mode fiber requires particularly high precision, with an accuracy of about 1 μm. must be done.

Conventionally, semiconductor lasers were formed as individual elements, and the alignment described above was performed when combining these elements to form a device, so the higher the precision required, the more difficult alignment became, resulting in lower yields. We were in a situation where it was declining. The reason why it has not been possible to form a guide mechanism for positioning integrally with a laser element in a semiconductor laser is as follows.

The first point is that the etching characteristics of compounds used in semiconductor lasers vary significantly depending on the crystal orientation. Therefore, it can be said that mirror etching becomes possible, but as a general tendency of single crystals of such compounds, it is the {111} plane, which is a high index plane, that is easily mirror etched. However, this surface is not orthogonal to the other low index surfaces {100} and {110}, so if you try to form a laser using the {111} surface as a reflective surface, the top or bottom surface will be The {111} reflective surface configuration is a relatively high-order index surface, and therefore it is difficult to control the processes necessary for laser formation, such as epitaxial growth and diffusion, on the relatively high-order index surface. They are in an extremely disadvantageous situation.

Second, the cleavage plane of the ZnS type crystal, which is the crystal type of the compound, is the {110} plane, but by mirror etching, especially selective etching of this plane, the {110}
One point is that it is generally difficult to obtain a mirror surface. {110} is orthogonal to {100}, and <110> are orthogonal to each other on {100}, which is the main surface of the laser, so it is easy to form a laser with the cleavage plane as the reflecting surface. In order to form a guide part for an optical fiber on the same crystal, this part cannot be separated by cleavage for forming a reflective surface, and therefore it must be connected to the guide part for an optical fiber. Reflective surfaces must be formed by means other than cleavage.

The present invention solves the above problems by applying the new knowledge obtained by the present inventors, and makes it possible to form an optical fiber guide groove on an extension of a striped laser region. It is something that

The present inventors have discovered that when an InP-based compound semiconductor is etched with a phosphoric acid (H ₃ PO ₄ )-based etching solution, not only the {111} A-plane but also the {110}-plane mirror surface can be obtained. In particular, when the {100} plane is selectively etched with an H ₃ PO ₄ -based etching solution, the etching holes that occur are composed of the {111} A plane in one direction, but are not formed by the {111} B plane alone in the orthogonal direction. Without,
It is composed of {110} plane and {111}B. That is,
Mask the {100} plane of InP and change the direction of the edges to <110>
If you open a rectangular window that matches the size and perform H ₃ PO ₄ etching, you will get an etched hole like the one shown in Figure 1. This means that both ends of the groove with a V-shaped cross section formed by the {111} A plane are {110} planes, and the vicinity of the bottom is {111}
It can be considered to be the B-side.

Although the above etching is possible with H ₃ PO ₄ alone,
Since the etching speed is slow, hydrochloric acid (HCl) is used for this.
By using an etching solution containing H ₃ PO ₄ /HCl, this V-groove etching can be carried out quickly. The above etching properties are exhibited up to a ratio of H ₃ PO ₄ :HCl of 1:2;
These properties are lost when the HCl fraction increases.

The present invention utilizes the crystal orientation dependence of H ₃ PO ₄ based etching of an InP substrate whose main surface is the {100} plane by such etching to form a V-groove for optical fiber alignment in the extended portion of the striped laser region. , and the {110} appearing at the end thereof is a reflective surface.

FIG. 2 shows a laser device of the present invention.

An active region 2 is formed in an InP single crystal 1, and a V-groove 4 is formed in the direction of light emission. The optical fiber 3 is fitted into this V-groove, and the position and width of the V-groove are determined so that the axes of the active region 2 and the core 3' of the fiber coincide.

Both side surfaces 5 of the V-groove are {111}A planes, but the end surface 6 in the axial direction is a {110} plane, which also serves as one reflective surface of the laser. The other laser reflecting surface 6' may be a cleaved surface as in the conventional case, or may be an etched mirror surface as in the embodiment of the manufacturing method of the present invention to be described later.

The formation of the striped laser oscillation region, except for the formation of both reflective surfaces, is all performed by known techniques, and is not intended to limit the implementation of the present invention.

Next, the configuration of the optical fiber alignment V-groove will be explained.

As shown in Figure 3a, <
An active region 2 extending in the 110> direction is formed by a known technique. Next, after masking the entire surface with an SIO ₂ film or the like, a window 8 is opened above the active region. It is desirable that this positioning be performed accurately, but it is practically sufficient if the degree of accuracy achieved by normal mask alignment is sufficient.

When this substrate crystal is subjected to the aforementioned H ₃ PO ₄ /HCl etching, a V-groove is formed as in the case of FIG. 1 (FIG. 3b). If this is cleaved using a knife edge 9 as shown, an InP laser with a V-groove structure as shown in FIG. 2 can be obtained.

In the above embodiment, the laser reflecting surfaces are formed on both sides by etching, but as described above, only the V-groove side needs to be etched, and the other side may be formed by cleavage. In that case, the positional relationship between the V-groove pattern and the cleavage plane is as shown in FIG.

The width of the V groove determines the depth of the groove,
Therefore, since the position of the core is fixed depending on the thickness of the optical fiber, it is uniquely determined by the outer diameter of the optical fiber used and the depth from the surface of the laser active region. . Since the length of the groove is only used for aligning the optical fiber, there is no need to make it longer than the necessary length for that purpose, for example, 1 mm, and the shorter the length, the more the same length as long as the above-mentioned effect is not lost.
The number of lasers that can be formed in InP crystal increases. Note that the length of the active region of the laser is approximately 200 to 300 μm. If the light output from the back side of the laser is also received by an optical fiber, the above-mentioned V grooves may be formed on both sides of the laser region.

An electrode metal layer is deposited on the upper surface of the laser region, but it is desirable to perform this step before forming the V-groove. Therefore, the electrode layer in this region is removed before opening the V-groove etching window. After coating with SiO _{2 ,} etc., a window is opened in the SiO ₂ layer so as not to expose the electrode layer. The purpose of this is to protect the electrode layer from being etched during V-groove etching.

As explained above, according to the method of the present invention, it is possible to easily form an InP laser having a V-groove for positioning an optical fiber, and in this laser, highly accurate positioning with the optical fiber can be easily performed. You get it.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an etching hole configuration surface in etching according to the method of the present invention, FIG. 2 is a diagram showing a laser device of the present invention, and FIGS. 3 and 4 are diagrams showing the manufacturing method of the present invention. In the figure, 1 is InP
Crystal, 2 is the oscillation region, 3 is the optical fiber, 3' is the same core, 4 is the V groove, and 5 is the side surface of the V groove {111}A
6 is the end surface of the V-groove and is a laser reflecting surface, 6' is the other laser reflecting surface, 7 is the {111} B surface, 8 is the V-groove etching window, and 9 is the knife edge. .

Claims (1)

[Claims] 1. A step of forming a striped laser oscillation region in a partial region of an InP-based compound semiconductor substrate whose main surface is a (100) plane, and aligning one side of a rectangular mask in the <110> direction. ,
Then, by selective etching using a phosphoric acid/hydrochloric acid etching solution, the end of the laser oscillation region has a cleavage plane, and if the optical fiber is held, it is aligned with the central axis of the optical fiber. 1. A method for manufacturing a semiconductor laser device, comprising the step of forming an alignment groove having a V-shaped cross section and aligned with the center axis of a stripe in a laser oscillation region.