JPS62166585A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To suppress the corrugation phase dependency of a reflecting mirror loss characteristic by roughly forming one of the end faces of a distributed feedback semiconductor laser in which a corrugation is formed near an active layer. CONSTITUTION:One 12 of the end faces of a semiconductor laser is formed roughly. That is, one of the two end faces is formed roughly so that the phase condition of a reflected light on the roughed end face is disordered. Thus, defects (which are decrease in an external differentiation efficiency per one end face, a decrease in a photon density in an active layer, a decrease in a high speed responsiveness, etc.) which indispensably occur when both end faces are formed in nonreflection are suppressed, and the corrugation (diffraction grating) phase dependency of the reflecting mirror loss characteristic can be suppressed in its limit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] This is an improvement of a distributed feedback semiconductor laser having a corrugation (diffraction grating) in the vicinity of an active layer.

The reflector loss characteristics of a distributed feedback semiconductor laser that has a corrugation (diffraction grating) near the active layer are highly dependent on the facet phase of this semiconductor laser, and the yield of single wavelength oscillation, external differential efficiency, and threshold value are greatly dependent on the facet phase of this semiconductor laser. This affects the current, etc., but in order to suppress this effect and improve manufacturing yield, one of the end faces of the semiconductor laser is made rough.

[Industrial application field]

The present invention has a corrugation (diffraction grating) near the active layer.
The present invention relates to improvements in distributed feedback semiconductor lasers having the following characteristics. In particular, it relates to improvements in controlling the corrugation (diffraction grating) phase dependence of reflector characteristics.

[Conventional technology]

One type of semiconductor laser is a distributed feedback semiconductor laser in which a corrugation (diffraction grating) is provided near an active layer.

The mirror characteristics of this distributed feedback semiconductor laser largely depend on the end facet phase. Namely.

As shown in Figure 7, the normalized reflector loss difference has a maximum value and a minimum value when the end face is approximately π/2 away from the peak of the corrugation (diffraction grating), and the difference between the maximum value and the minimum value. The difference amounts to approximately 0.5.

In the figure, 0=0 or θ=2π means that the end face corresponds to the peak of the corrugation (diffraction grating), and θ=
π means that the end face corresponds to the valley of the corrugation (diffraction grating).

This fact means that if the position of the end face is selected so that the end face coincides with a specific value of the corrugation phase, the single-reflector characteristics will be the best and most desirable. However, the pitch of a corrugation (diffraction grating) is generally several thousand, which is extremely small, and it is difficult to detect the phase of a corrugation (diffraction grating) (whether a certain surface is a peak or a valley). , it is generally not easy to form an end face at a specific position of the corrugation phase.

Variations also increase, and when mass production is assumed, there are problems with yield.

Therefore, in the prior art, a silicon nitride film or the like is formed on both end faces to a thickness of 1/4 to form a non-reflective coating film to suppress reflection and alleviate the above-mentioned drawbacks.

[Problem that the invention seeks to solve]

However, in the semiconductor laser using the above-mentioned non-reflection coating film, since the non-reflection coating film is provided on both end faces, laser light is also extracted from the rear end face, so the amount of light per end face is Not only does the external differential efficiency become smaller.

There are unavoidable drawbacks such as a decrease in photon density in the active layer and a decrease in high-speed response.Furthermore, bimodal oscillation, which is characteristic of a distributed feedback structure, is likely to occur, resulting in a reduction in single oscillation yield. It has the disadvantage that it also deteriorates.

An object of the present invention is to provide a semiconductor laser in which the corrugation (diffraction grating) phase dependence of the reflector characteristics is suppressed without having these drawbacks.

[Means for solving problems]

The means taken by the present invention to achieve the above object is to roughen one end face of a distributed feedback semiconductor laser in which a corrugated grating (diffraction grating) is formed near the active layer 3. It is in.

A suitable method for producing this rough surface is a sandblasting method, and the degree of unevenness is preferably about the intracrystalline wavelength.

[Effect]

It is well known that regular reflection can be suppressed by roughening the end face.

Therefore, only one of the two end faces is roughened, and the phase condition of the reflected light on this roughened end face is made disordered. This eliminates the above-mentioned drawbacks (decreased external differential efficiency of one end surface, decreased photon density in the active layer, decreased high-speed response, etc.) that would inevitably occur if both end surfaces were made non-reflective. While suppressing the occurrence of
This suppresses the corrugation (diffraction grating) phase dependence of the reflector loss characteristics to its limit.

〔Example〕

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A distributed feedback semiconductor laser according to an embodiment of the present invention having an indium gallium arsenide layer as an active layer will be described below with reference to the drawings.

An n-type indium phosphorus substrate 1 was prepared using the liquid phase growth method (see Figure 2).
On top, an n-type indium gallium arsenide layer (0,
15gm thick) 2 and indium gallium arsenide layer (
0,15, ■ thickness) 3 and p-type indium phosphorus layer (approx. 1
．． 5 pm thick) 4 and a p-type indium gallium arsenide layer 5 (0.5 pm thick) are successively formed. The n-type indium phosphorus substrate l serves as an optical confinement layer, the n-type indium gallium arsenide layer 2 serves as a guide layer, the indium gallium arsenide layer 3 serves as an active layer, and the p-type indium phosphorus substrate 1 serves as an optical confinement layer. The murine layer 4 serves as a light confinement layer.
The p-type indium gallium arsenide layer 5 functions as a cap layer.

Using a lithography method (see FIG. 3), a mask 6 made of silicon dioxide is formed in a stripe region with a width of about 3 gm,
Using this mask 6 and using bromine methanol or the like, p-type indium gallium arsenide layer 5, p-type indium phosphorus layer 4, indium gallium arsenide phosphide M3, and n-type indium Dium gallium phosphorus layer 2
and remove. At this time, the upper layer of the substrate 1 is also inevitably removed.

Refer to Figure 4. Using the liquid phase growth method again, p-type indium phosphorus R
(approximately 1.5 Bm thick) 7 and an n-type indium phosphorus layer (approximately 1IL layer thickness) 8 are formed to form the northern part of the current limit.

Next, silicon dioxide 719 is formed and removed from the stripe area.

Referring to FIG. 5, a titanium/platinum/gold layer lO is formed on the upper surfaces of the silicon dioxide layer 9 and the p-type indium gallium arsenide layer 5 to form a positive electrode, and a gold/platinum layer lO is formed on the lower surface of the substrate l. A germanium/gold layer 11 is formed to form a negative electrode.

The wafer is cut into an array in the direction perpendicular to the optical axis A, see FIG. 6. This array includes a plurality of distributed feedback semiconductor lasers 15.
are formed so that their leading axes A are aligned in parallel, and the end faces 13 and 14 are the cut out faces.

An anti-reflection coating g13 is formed on one end surface I2, and the other end surface 14 is roughened by sandblasting. The degree of unevenness of the rough surface is approximately equal to the intracrystal wavelength.

Refer to FIG. 1. Each element is cut out to complete the distributed feedback semiconductor laser 15. In addition, in the figure, 17 is a stripe.

〔Effect of the invention〕

As explained above, since one of the end faces of the semiconductor laser according to the present invention is roughened, the above-mentioned drawback (the external To provide a distributed feedback semiconductor laser that suppresses the corrugation (diffraction grating) phase dependence of reflector loss characteristics without causing a decrease in differential efficiency, a decrease in photon density in the active region, a decrease in high-speed response, etc. I can do it.

[Brief explanation of drawings]

FIG. 1 is a plan view of a distributed feedback semiconductor laser according to an embodiment of the present invention. 2 to 6 are cross-sectional views of a substrate illustrating the manufacturing process of a distributed feedback semiconductor laser according to an embodiment of the present invention. Figure 7 shows a corrugation (diffraction grating) near the active layer.
3 is a graph showing the relationship between the normalized reflector loss difference and the phase of a distributed feedback semiconductor laser having the following characteristics. 1I111・Indium phosphorus substrate, 2・N-type guide layer made of indium gallium arsenide phosphide,
3. Φ. Active layer made of indium gallium arsenide phosphide, 4... Optical confinement layer made of p-type indium gallium arsenide phosphide, 5. Cap layer made of p-type indium gallium arsenide phosphide, 6・e・mask, 7・map type indium phosphorus layer, 8・・
・N-type indium phosphorus layer, 9...Silicon dioxide layer, 1O...Positive electrode, 11.Φ-Negative electrode, 1
2...One end surface, 13φ/φ anti-reflection coating film, 1
4...Other end surface (rough end surface), 15...
A distributed feedback semiconductor laser according to the present invention. Fig. 2 Fig. 3 Fig. 4 Fig. Process drawing No. 5 Artwork T'4 i'4 No. 6 Invention No. 1121 4 Iriro 12 Koi tV Figure 7

Claims (1)

[Claims] In a distributed feedback semiconductor laser in which a corrugation (diffraction grating) is formed in the vicinity of an active layer (3), one of the end faces (12) of the semiconductor laser is a rough surface. A semiconductor laser characterized by: