JPH01321676A - Semiconductor laser and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a laser resonance surface having no etching nonuniformity and excellent flatness by forming a laser reflecting surface shaping the angle of 90 deg. or 45 deg. to an active layer onto the side face of a broad striped region and forming an electrode onto a narrow striped region. CONSTITUTION:An upper side clad layer 4 is shaped by a narrow striped section 6 as a narrow striped region and a broad striped section 7 as a wide striped region. A 90 deg. mirror 11 is formed to the broad stripe 7 as a laser reflecting surface having the angle of 90 deg. to an active layer 3. A p side electrode 10 is arranged onto the narrow striped section 6 and an n side electrode 15 onto a substrate 1. Consequently, since a laser principal section is composed of narrow ridge stripes, beam spot size on a laser resonance surface is determined by the width of the narrow ridge stripe sections. Accordingly, when the width of the ridge stripes near the laser resonance surface is widened sufficiently, the effect of the etching nonuniformity of the side faces of the ridge stripes can be eliminated approximately, thus easily acquiring the laser resonance surface oscillated at a low threshold.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser used in the fields of optical information processing and optical communication, and more particularly to a ridge stripe type laser.

(Problems with Prior Art) Semiconductor lasers are small and consume low power, and are therefore widely used in optical information processing, optical communications, and the like. Furthermore, optical ICs in which a large number of semiconductor lasers are integrated are also being actively researched. High yield and uniformity are strongly required for semiconductor lasers mounted on optical ICs. On the other hand, ridge stripe lasers are easy to manufacture, have high yield, and have good uniformity, and are important semiconductor lasers as light sources for optical ICs (for example, IEICE technical research report 0QE85- 81). However, light I
When semiconductor lasers are mounted in a matrix in C, it is difficult to obtain a laser resonant surface (laser reflection surface) between the folds, so it is necessary to form the laser resonant surface by etching. The most efficient method for etching a laser resonant surface is a method called active ion beam etching (abbreviated as RIBE method).

This is a method of etching by irradiating a sample with ions in the form of a beam, and because the etching side surface has excellent flatness and linearity, a laser resonant surface can be easily formed. However, when the laser resonant surface of the above-mentioned ridge stripe laser is created by the RIBE method, there is a problem that etching of the side surfaces of the ridge stripe is slow and uneven etching tends to occur. For this reason, the flatness of the laser resonant surface of the manufactured ridge stripe laser is poor, and the mirror loss increases, resulting in a problem that the oscillation threshold current increases.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a ridge stripe type semiconductor laser which is free from the above-mentioned etching unevenness and has a laser resonant surface with good flatness, and a method for manufacturing the same.

(Means for Solving the Problems) In order to solve the above problems, a semiconductor substrate, a lower cladding layer formed on the semiconductor substrate, an active layer formed on the lower cladding layer, In a ridge stripe type semiconductor laser which is formed on this active layer and has an upper cladding layer including a ridge stripe-like structure, the upper cladding layer has two wide stripe-like regions and a width connecting these regions. The narrow stripe-like region has a ridge stripe structure consisting of a narrow stripe-like region, and a laser reflecting surface is provided on the side surface of the wide stripe-like region, which is perpendicular to the active layer or at an angle of 45°. A semiconductor laser characterized in that an electrode is provided on the semiconductor laser. The method for manufacturing this semiconductor laser includes a step of forming a lower cladding layer on a semiconductor substrate, a step of forming an active layer on top of the lower cladding layer, a step of forming an upper cladding layer on top of the active layer, and a step of forming at least a part of the upper cladding layer. A process of removing by etching to form a ridge stripe-like structure consisting of two wide stripe-like regions and a narrow stripe-like region connecting the two wide stripe-like regions, and removing the wide region of the stripe using dry etching. The method is characterized in that it includes a step of etching a part of the surface to form a laser reflecting surface.

(Function) The following reasons are considered to be the cause of the etching unevenness in the conventional semiconductor laser and its manufacturing method described above. That is, in the RIBE method, etching species (for example, Cl ions) fly in the form of a beam and react with the semiconductor. The reaction products produced by the reaction evaporate, but some of them adhere to the semiconductor surface again.

This redeposited reaction product is usually etched and evaporated by a subsequent etching beam. However, the situation is slightly different when etching a semiconductor having stripe-like protrusions such as ridge stripes and large irregularities. That is, since the side surfaces of the ridge stripe are substantially parallel to the etching beam, the etching beam is not directly irradiated onto them. For this reason, the reaction products adhering to the side surfaces of the ridge stripe are not etched and are deposited thickly, resulting in a problem that the etching of the side surfaces of the ridge stripe is extremely slow. Therefore, in conventional manufacturing methods,
As shown in FIG. 1, etching unevenness 13 occurs on the side surface of the ridge stripe, and the laser output light is scattered at this portion, resulting in a problem of increased mirror loss.

Therefore, in the present invention, in order to eliminate the influence of the above-mentioned etching unevenness, the ridge stripe is widened only in the vicinity of the laser resonant surface. In this case, since the main part of the laser is composed of a narrow ridge stripe, the beam spot size on the laser resonant surface is determined by the width of the narrow ridge stripe. Therefore, compared to the width of the beam spot,
By making the width of the ridge stripe near the laser resonant surface sufficiently wide, the influence of uneven etching on the side surfaces of the ridge stripe can be almost eliminated. Therefore, a ridge stripe laser having a laser resonance surface by dry etching that oscillates at a low threshold value can be easily obtained.

(Example) Next, the present invention will be explained in detail using examples.

FIG. 1 is a cross-sectional structural view perpendicular to the resonance plane of a semiconductor laser according to a first embodiment of the present invention. In this figure, the upper cladding layer 4 is formed of a narrow stripe portion 6 as a narrow stripe-like region and a wide stripe portion 7 as a wide stripe-like region. Further, a 90° mirror 11 is formed on the wide stripe 7 as a laser reflecting surface having an angle of 90° with respect to the active layer 3. A P-side electrode 10 is arranged on the narrow stripe portion 6, and an N-side electrode 15 is arranged on the substrate 1. A semiconductor laser with this structure is shown in Figure 2(a).
, (b), (c), and (d).

First, as shown in Figure 2(a), a double heterostructure is formed by n-G
A crystal is grown on the aAs substrate 1. The growth method may be any growth method such as a molecular beam epitaxy (MBE) method or a vapor phase growth method. This double heterostructure is A lGaA
It is made of s/GaAs material and has an n-type cladding layer 2.
(n AlxcGat-xcAss Xc=0.3~
0.7, thickness 1-3μm) active layer 3 (GaAs1 thickness 500-200OA), P-type cladding layer 4 (PA
1xcGa+-x.

AS1 thickness 1-3 μm), cap layer 5 (P”-G
aAss thickness 2000-5000A).

Next, as shown in FIG. 2(b), a ridge stripe 8 consists of a narrow stripe portion 6 as a narrow stripe-like region and a wide stripe portion 7 as a wide stripe-like region.
form. The etching method may be either a chemical etching method or a dry etching method. The width of the narrow stripe portion 6 is 1 to 5 μm. The width of the wide stripe portion 7 is approximately 20 μm, which is 10 to 20 μm wider than the narrow stripe portion. If the width of the wide stripe portion 7 is too narrow (then the RIBE
90° mirror 11 of the laser reflecting surface formed by
Etching unevenness during etching is laser spot 1
If the value is too close to 2, the laser characteristics will be impaired. On the other hand, if the width of the wide stripe section 7 is made too wide, current leakage to both sides of the wide stripe section 7 may increase, which is not preferable. The height of the ridge stripe 8 is such that the thickness of the P-type cladding layer 4 at the bottom of the ridge stripe 8 is 1000~
A value of 3000 A is preferable for controlling the transverse mode of the laser and suppressing leakage current in the transverse direction. Next, Figure 2 (
As shown in C), a SiN film 9 is formed, and then the SiN film is removed only from the narrow stripe portion 6. The removal process involves coating the photoresist and then etching the resist by dry etching at 0°. In this case, since the top of the narrow stripe portion 6 is protruding, the narrow stripe portion 6
It is a good idea to take advantage of the fact that the photoresist on the top of the photoresist is removed. Next, the P-side electrode 10 is formed, and the P-side electrode 9 and the SiN film 10 other than the narrow stripe portion 9 are removed by photoetching. Next, as shown in FIG. 2(d), a 90° mirror 11 is formed by etching using RIBE. In this example, a 90° mirror 11 with good perpendicularity and flatness was obtained by the RIBE technique in which CI ions and CI radicals are generated using ECR plasma. Furthermore, when etching the side surface of the wide stripe section 7, etching unevenness 13 occurs, but since this is separated by light from the laser spot 12, the effect of the etching unevenness 13 is almost negligible, and good optical output characteristics are achieved. Obtained. Furthermore, if the length of the wide stripe portion 7 in the resonator direction is too long, light absorption loss will increase, which is not preferable. This is because no electrode is provided in the wide stripe portion, so it is non-excited and absorbs a large amount of light. However, if the length of the wide stripe portion 7 is too short, alignment in the photo-etching process becomes difficult, which is not preferable. Therefore, in this embodiment, the length of the wide stripe portion in the resonator direction is approximately 3 to 5 μm.

Next, a second embodiment will be described. FIG. 3 shows a semiconductor laser according to a second embodiment and a method for manufacturing the same. The difference from the first embodiment is the step (d) in FIG. In this step, a reflective surface is formed using RIBE technology. In this process, one side is a 90" mirror, and the other side is a 45° mirror tilted at 45°. In this way, the light inside the semiconductor laser is vertically reflected at the 45° mirror, so that the laser output light 22 is n- G
The light is emitted perpendicularly to the aAs substrate. In this case as well, if the 45° mirror 20 is formed on the ridge stripe 8, an etching difference 21 will be produced on the side surface of the ridge. However, according to the manufacturing method of the present invention, the width of the wide stripe portion 7 is 45°, which is sufficiently narrower than the width of the laser internal light reflected by the mirror 20, so that high efficiency laser output can be achieved without being affected by the etching difference 21. It was possible to extract the light 22 in the plane direction.

In the embodiments described above, the active layer has a single layer structure, but it may also have a structure with a light guide layer or a multilayer structure such as a multiple quantum well structure. In addition, in this example, A is used as the material system.
lGaAs/GaAs system was used, but it is not limited to this.
nGaAs P/I nP system, I nAlGaAs/I
It goes without saying that this method can also be applied to other materials such as nP-based materials.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional structural diagram of a semiconductor laser according to a first embodiment of the present invention, FIG. 2 is a diagram showing its manufacturing method, and FIG. 3 is a semiconductor laser according to a second embodiment of the present invention and its manufacturing method. FIG. In the figure, l is an n-GaAs substrate, 2 is an n-type cladding layer, and 3
is an active layer, 4 is a P-type cladding layer, 5 is a cap layer, 6 is a narrow stripe portion, 7 is a wide stripe portion, 8 is a ridge stripe, 9 is a SiN film, 10 is a P-type electrode, 11 is a 90″
12 is a laser spot, 13 is an etching unevenness, 14 is a laser output beam, 15 is an n-side electrode, 20 is a 45
° A mirror, 21 an etching gap, and 22 a laser output beam.

Claims (2)

[Claims] (1) A semiconductor substrate, a lower cladding layer formed on this semiconductor substrate, an active layer formed on this lower cladding layer, and a ridge stripe-shaped structure formed on this active layer. In a ridge-stripe semiconductor laser, the upper cladding layer has a ridge-stripe structure consisting of two wide striped regions and a narrow striped region connecting these regions. A laser reflecting surface is provided perpendicularly to the active layer or at an angle of 45° to the active layer on the side surface of the wide striped region, and an electrode is provided on the narrow striped region. semiconductor laser. (2) Forming a lower cladding layer on the semiconductor substrate, forming an active layer on top of the active layer, forming an upper cladding layer on top of the active layer, and removing at least a portion of the upper cladding layer by etching. A step of forming a ridge stripe-like structure consisting of two wide stripe-like regions and a narrow stripe-like region connecting the middle, and dry etching are used to partially remove the wide stripe-like region. Claim 1, characterized in that it includes a step of etching to form a laser reflective surface.
The method for manufacturing the semiconductor laser described in Section 1.