JPS6016489A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To contrive to increase the output by the radiation of a laser beam of uniform basic lateral modes by a method wherein a reflection plane corresponding to an active layer is provided with a photo absorption film with a hole of the shape of said mode bored. CONSTITUTION:A clad layer 12, the active layer 13, and a clad layer 14 of required thicknesses are epitaxially grown on a crystal substrate 11 successively. Next, a stripe conductive region 16 is formed in the clad layer 14 by means of a mask of a required width. A passivation film SiO2 1 is adhered to the end surface of a stripe structure planar type semiconductor laser thus formed. This element is incorporated in a sub mount system, and then a resist material 2 corresponding to photo distribution is formed by the heat at the end surface under laser generation. Thus, the part of the material 2 is changed into the photo absorption film of the hole of the shape of the mode. Then, the semiconductor laser is increased in the output by the radiation of the laser beam of uniform basic lateral modes.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser device, and more specifically to a double hetero type semiconductor laser device having striped electrodes.

Semiconductor laser devices generally have a double heterostructure with good light confinement in the junction region.

This double heterostructure is formed by forming semiconductor layers with a low refractive index and a large forbidden band energy on both sides of a so-called active region where laser oscillation or optical modulation is performed.

Such a semiconductor laser is expected to be a light source that can be applied to a wide range of fields such as optical communications, optical information terminals, video disks, and measurement.

In these applications, it is desirable to obtain as high an optical output as possible while keeping the transverse mode of the laser in the fundamental mode. On the other hand, typical examples of conventional transverse mode-controlled lasers include Bl (laser) and C8P laser, but all of these require complex processes and equipment for crystal growth, and cannot be mass-produced at low cost. There is a problem in producing such devices.

Among the lasers that oscillate in the transverse fundamental mode, the one with the simplest structure is the so-called narrow fist stripe (Narrate stripe).
row 5tripe) structure, 1 As shown in Fig. 1, the width W of the stripe electrode 16 This type of laser can obtain an optical output of about 5 mW in the transverse fundamental mode, but the practical difficulty is that , since the lateral optical guide +° is a so-called gain guide, the wavefront of the laser beam does not become a plane wave, resulting in astigmatism.In particular, when the laser beam is narrowed down to a spot diameter of 10 μm or less, it is used. A light source with such astigmatism cannot be used in applications.To improve this point, Narrow 5tripe
A known method is to fabricate a mode filter that transmits only the fundamental mode and absorbs or scatters higher-order transverse modes on the laser end face that forms the optical resonator of a type laser, in a self-aligned manner with respect to the stripe electrode. ing. To do this, we first deposited a low melting point thin film such as tellurium (Te), which is used in so-called optical recording video disks, as shown in Figure 2 (a).
) is deposited on the laser end face. Next, when a large current is passed through the laser element, the portion of the Te film that absorbs the laser light is instantaneously evaporated, creating a hole in the Te film in the shape of the laser oscillation mode. This method shown in Figure 2(b) allows the mode filter to be fabricated in self-alignment with respect to the stripe electrode position and light distribution, but the drawback is that it requires a pulsed light output of 20 mW or more to evaporate the Te film. is necessary. In such a high optical output state, the transverse mode of the Narrow Stripe laser generally includes higher-order mode components, and the resulting mode filter does not necessarily pass only the transverse fundamental mode.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a semiconductor laser that oscillates in a transverse fundamental mode and is easy to process and grow crystals.

The structure of the present invention for achieving the above object is to provide a light absorption film having holes in the shape of a fundamental transverse mode on a reflective surface corresponding to an active layer of a laser element. This light absorption film is
Any type of film that absorbs, scatters, or reflects light may be used as long as it has the effect of cutting off laser light that contains higher-order transverse modes other than the fundamental transverse mode, that is, laser light that spreads laterally more than necessary. . In a laser like this, in which the fundamental mode filter is formed on the laser end face to narrow the emission frontage, the astigmatism that was inherent in the conventional Narrow 5tripe type is eliminated, and the laser beam can be transmitted very easily by using an optical lens, etc. It is possible to focus light to a spot diameter of about 1 μm.

The laser device of the present invention emits laser light after a negative photoresist film is once deposited on a mirror surface, and exposes it in the form of an (elliptical) spot.

This exposed area approximately corresponds to the shape of the fundamental transverse mode. Higher-order transverse modes other than the fundamental transverse mode are either absorbed by the resist material or are not strong enough to be exposed until they are exposed, so that they are eventually exposed in the form of the fundamental transverse mode as described above. Leaving this exposed area, the resist material in other areas is removed, and a metal thin film is deposited on the mirror surface. Afterwards, by removing the exposed photoresist using a material solvent or the like, a semiconductor laser device having a light absorption film having holes in the shape of the fundamental transverse mode is obtained. As described above, the laser device of the present invention can be formed extremely easily by using ordinary semiconductor manufacturing technology without using any new process technology. This will be explained in detail below using examples.

FIGS. 3A to 3C are perspective views schematically showing a semiconductor laser device and its manufacturing process as an embodiment of the present invention.

Figure 3(a) shows carrier concentration 2X doped with Si.
1018 cm-3 GaAs (100) TJ crystal substrate 1
1, by a well-known liquid phase epitaxial growth method, a 1.5 μm thick Te (tellurium) doped film with a carrier concentration lX
l0 cm of n-Ga, 7 AJo, 3 As
A cladding layer 12 with a thickness of 0.1 μm is similarly applied on the layer 12.
An active layer 13 of undoped GaAs of m, in the soil of the layer 13,
・Similarly, thickness 1.5 μm 1 carrier concentration I x 101
8 cm"" p-Ga o, 7 Al o, a
A cladding layer 14 of As is formed. Next, a mask made of an SiO2 film having stripe-shaped openings with a width of 3 to 4 μIn is formed on the cladding layer 14, and striped conductive regions 16 are formed. If necessary, an n-GaAs cap layer may be provided on the cladding layer 14, and a p4Iit9i region may be formed by Zn diffusion in the cap layer. In this case, the mask for selective diffusion of Zn is removed and a 5in2 film with a thickness of 5000 mm is formed again.

Openings similar to those of the striped conductive regions described above are formed in this SiO□ film using a normal photolithography technique. Next, Cr and Au are deposited on the entire surface to form an n-side electrode. Note that this n-side electrode portion is not shown. In addition, after shaping the back surface of the semi-grain substrate 11 and lightly etching it, Au −
A Ge alloy is deposited to form an n-side electrode (not shown). The resonator length was 300 μm. As shown in FIG. 3(a), a passivation film 1 is applied to the end face of the conventional striped planar semiconductor laser thus formed.

(For example, a 5io2 film formed by sputtering) λ Here, it is important that the film thickness is 5 x n. However, λ is the wavelength of the laser light in the film (usually 4000 to 8000
person), n is an integer. After that, the laser element is assembled into a submount and a stem, and then placed in a negative photoresist and a current is applied to cause laser oscillation. At this time, it is necessary to confirm that the laser oscillates in the transverse fundamental mode with a low optical output of about 3 mW. Due to the laser light and heat generation at the end face, a photosensitive resist part with a shape corresponding to the light distribution is formed on the end face of the laser, and after cleaning with a resist development wave, the hardened resist 2 as shown in Figure 3 (bl) is formed. remains.

Next, a thin film that slightly changes the reflectance of the laser beam at the end face is applied by vapor deposition or sputtering to the end face. As such a film, a metal film (Au%) that absorbs light is used.
AJ) may be used, or a transparent dielectric film may be attached to the film 21 at or near 7Xm. However, m is an integer. Alternatively, it may be a uniform film in the form of fine particles that scatters light.

After that, the hardened resist part was removed by attaching a chip to J100 using the lift-off method, as shown in Figure 3 (C
), a membrane with a hole in the shape of the fundamental transverse mode remains on the end face. Since this film acts as a mode filter, the transverse mode of the semiconductor laser is limited to the transverse fundamental mode up to an optical output of about 20 m1V.

As described in detail above, the present invention makes it possible to emit laser light with tT+il in the fundamental transverse mode by providing a light absorption film with holes in the fundamental transverse mode at a predetermined location on the mirror surface of the laser element. The fact that it has been made easy is of great industrial benefit.

In the embodiment of the present invention, the semiconductor material is GaAs-G
Although the aA/As-based laser has been described, those skilled in the art will understand that the present invention is applicable not only to this material but also to double-hetero type lasers using general semiconductor materials such as GaAsP and InGaAsP. It will be easily understood.

[Brief explanation of drawings]

1 and 2 are a schematic cross-sectional view and a perspective view of a conventional semiconductor laser device, and FIG. 3 is a schematic perspective view of a semiconductor laser device as an embodiment of the present invention. 1... Passivation film (Si02) Th2...
V cyst material, 3... light absorption film (metal thin film). Figure 1 Day 2 Figure 3

Claims (1)

[Claims] A semiconductor substrate, an active layer formed on the substrate, a striped electrode formed to supply a forward operating current to the active layer, and an optical resonator formed to oscillate laser light. A semiconductor laser device having two mutually parallel reflecting surfaces, characterized in that the reflecting surface corresponding to the active layer is provided with a light absorption film having a hole in the shape of a fundamental transverse mode. .