JP2564343B2 - Semiconductor laser device - Google Patents

Description

The present invention relates to a structure of a semiconductor laser having low aberration and low noise and a method for manufacturing the same, and more particularly to a laser structure having a small change in luminous efficiency.

[Conventional technology]

In a so-called refractive index guided device in which the laser light distribution (transverse mode) of the semiconductor laser is confined by the refractive index difference between the inside of the stripe and the outer edge portion, the oscillation spectrum line (longitudinal mode) is single. When such an element is applied to an optical disc, return light noise occurs due to reflected light from the disc. On the other hand, in an element with a small difference in refractive index, the longitudinal modes are multi-stated and return optical noise does not occur, but the position of the beam waist in the direction perpendicular to the active layer is different, and so-called astigmatism is closed. The drawback is that the beam cannot be narrowed down. Therefore, it is desired to use an element having a multimode longitudinal mode and no astigmatism. To this end, the above object can be achieved by changing the stripe structure in the optical axis direction of the semiconductor laser so that the refractive index difference is small inside the element and the refractive index difference is large near at least one end face. There are already reports about such devices,
With the introduction of the strong waveguiding region for the correction of astigmatism, the emission efficiency was decreased. It is considered that this is due to the difference in spot size between the gain guide region and the strong guide region. That is, it is considered that when the stripe width is designed to be the same, the spot size of the strong guide region becomes smaller than the spot size of the gain guide region, so that the laser light is strongly lost in the strong guide region.

Regarding the rib optical waveguide mode filter type laser, the 31st meeting on conformity lecture 4-2 (Sho 57.3.29), Japanese Patent Laid-Open No. Sho 60
-Published in 198795.

[Problems to be solved by the invention]

An object of the present invention is to provide a semiconductor laser having good noise characteristics and no astigmatism, and particularly to optimize the stripe width of this semiconductor laser for each region to obtain a semiconductor laser with higher efficiency. To aim.

[Means for solving problems]

To achieve the above object, in the present invention, the stripe width in the vicinity of the end face of the semiconductor laser, which is the gain guide in the central part of the semiconductor laser and is the refractive index guide in the vicinity of the end face, is larger than that in the central part, for example, 0.5 μm or more. I devised to be thick.

 That is, the present invention has the following configurations.

At least to give the semiconductor medium optical gain,
It has a junction of semiconductors of different conductivity types and a stripe-shaped optical waveguide mechanism provided on this junction surface, and the optical waveguide mechanism mainly uses the gain difference between the inside and outside of the stripe at the center of the laser. The difference in refractive index between the inside and outside of the stripe is mainly used near the end face, and the stripe width of the laser end face region is widened so that the light spot size in the laser end face region is larger than the light spot size in the laser central region. A semiconductor laser device characterized by the above.

[Action]

According to the present invention, a laser having a lower threshold and a higher efficiency can be obtained by using a refractive index waveguide type waveguide and a semiconductor laser only near the end face.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

Example 1 A semiconductor laser structure of Example 1 of the present invention will be described.
A recess (2) as shown in FIG. 1 is formed on the p-type GaAs substrate (1).
The n-GaAs layer (3) was formed by chemical etching using a SiO ₂ mask formed by a normal photolithographic technique, and by MOCVD. Next, a groove (4) serving as a waveguide as shown in FIG. 1 was formed. The groove is formed to have a width of 5 to 7 μm in the portion sandwiched by the recesses of the substrate, and is formed to have a width of 3 to 5 μm in the other regions. The depth of the groove and the depth of the recess were 2 and 4 μm, respectively. After that, as shown in FIG. 2, a p-Ga _0.5 Al _0.5 As cladding layer (5), an undoped Ga _0.86 Al _0.14 As active layer (6), an n-Ga _0.5 Al _0.5 As cladding layer (7), n -GaAs
The cap layer (8) is grown sequentially. Next, AuGeNi / Cr / Au
The electrode (9) and the Cr / Au electrode (10) are deposited. After this,
FIG. 2 Cleaves at the alternate long and short dash line portion (aa) to form an anti-slope. FIG. 2 (a) is a sectional view near the end face,
Due to the influence of the recess, the n-GaAlAs cladding layer and the active layer formed on the groove are thinner than the central portion of the element as shown in FIG. 2 (b). FIG. 2 (a) is a perspective view, and FIG. 2 (b) is a sectional view taken along the plane aa. Therefore, a large difference in refractive index occurs in the horizontal direction, and the laser light is confined by this, so that the astigmatism is small. In order to increase the difference in refractive index, it is necessary to increase the influence of the n-GaAs substrate. Therefore, the thickness of the outer edge of the groove of the p-type cladding layer is 0.4 μm or less, and the thickness of the active layer 6 is 0.7 μm or less. There is a need to.
On the other hand, in the central portion of the element shown in FIG.
Since the As cladding layer and the active layer are both thick, the difference in the refractive index is small, so that the mode becomes multi-mode and no optical feedback noise occurs. In order to reduce the difference in refractive index, it is necessary to reduce the influence of the p-GaAs substrate. Therefore, the thickness of the outer edge of the groove of the p-type cladding layer should be 0.4 μm or more, and the thickness of the active layer 6 should be 0.07 μm or more. There is a need to. The former is 0.7μm or less and the latter is 0.1μm.
Below m, the mode becomes multi-mode with pulsation, and noise is further reduced. The thickness of other layers is 0.8-2.0μm for n-type cladding layer and 0.5-5.0μm for n-type capping layer.
m. The AlAs composition of each layer is such that layers 5 and 7 are 0.35-0.55 layer 6
Is 0.05-0.20. In this device, the longitudinal mode is multi-mode and the relative noise intensity is 1 × 10 regardless of the amount of returned light.
^-13 Hz ^-1 or less. The astigmatism was 5 μm or less.

[Second Embodiment] As a second embodiment of the present invention, the same effect as that of the first embodiment is obtained by MO.
A prototype as shown in Fig. 3 was realized by using the CVD method. FIG. 3 (a) is a perspective view, and FIG. 3 (b) is an aa plane sectional view. Embodiments of the present invention will be described below with reference to the drawings. n
N-Ga _0.5 Al _0.5 As on -GaAs substrate (11) by MOCVD
Cladding layer (7), undoped Ga _0.86 Al _0.14 As active layer (6), p-Ga _0.5 Al _0.5 As cladding layer (5), p-Ga
_{A 0.7} Al _0.3 As layer (12) was sequentially grown. Then, usually using photolithographic techniques, first the Si ₃ N ₄ mask (13)
Was formed in a stripe shape having a width of 100 μm in the direction orthogonal to the stripe. Further, after forming a SiO ₂ film by the thermal CVD method, the photoresist process was used again to provide a two-layer mask of a SiO ₂ mask (14) and a photoresist. Etching of SiO ₂ was performed by using an HF-based etching solution, and etching of Si ₃ N ₄ , which has a slower etching rate than SiO _2, was performed by plasma etching with CF ₄ . Using a phosphoric acid-based etching solution, the p-type cladding layer outside the stripe is 0.1 to
Etching was performed with 0.3 μm left, and side etching of the mask was performed with an HF-based etching solution.
A mask having a shape as shown in the figure is obtained. This SiO ₂ / Si ₃
Selective crystal growth of n-GaAs (3) is performed using the N ₄ composite film as a selective growth mask, and after removing the SiO ₂ / Si ₃ N ₄ composite film with an HF-based etching solution, a shear etch for improving the surface condition is performed. Then, again by the MOCVD method, a p ⁺ -Ga _0.5 Al _0.5 As layer {p> 10 ¹⁹ cm ^-3 } (17), a p-Ga _0.5 Al _0.5 As layer (15),
It was filled with a p-GaAs cap layer (16). In this structure, Cr / Au (10) is used as the p electrode and AuGeNi / Cr / Au is used as the n electrode.
(9) was vapor-deposited and cut into a 300 μm square to make a laser chip. According to this structure, since the current narrowing width is narrow in the center of the laser, a gain waveguide type waveguide is formed. Is the main waveguiding mechanism and corrects the beam shape and astigmatism of the multimode laser.
Moreover, since the width of the waveguide in the laser end face portion of this structure is wider than in the laser central portion, the effect of improving the light emission efficiency is obtained as in the first embodiment.

[Third Embodiment] As a third embodiment of the present invention, an example in which an element having the same performance as that of the first and second embodiments is manufactured by double growth by the MOCVD method will be described. This will be described with reference to FIG. FIG. 5 (a) is a perspective view,
FIG. 5 (b) is a sectional view of the aa plane. An n-Ga _0.5 Al _0.5 As cladding layer (7), an undoped Ga _0.86 Al _0.14 As active layer (6), and a p- layer were formed on the n-GaAs substrate (11) by MOCVD.
Ga _0.5 Al _0.5 As cladding layer (5), first p-Ga _0.7 Al _0.3
As layer (12), first p-Ga _0.5 Al _0.5 As layer (12), second p-Ga _0.7 Al _0.3 As layer (12), second p-Ga _0.5 Al _0.5 As layer (15) , P-GaAs cap layer (16) was successively grown, and then a stripe-shaped SiO ₂ mask (14) was provided by using a normal photolithographic technique. Next, a p-GaAs layer was removed by chemical etching after again providing a mask so as to protect the region to be the laser end face by using the photograph technique. Further, SiO ₂ used for the etching mask was used as it was to etch to the p-type selective etching layer which was subjected to Ar ion etching, and the remaining selective etching layer was removed by boiling hydrochloric acid. Boiled hydrochloric acid is p-Ga
_Since only the _0.5 Al _0.5 As layer is etched and the p-Ga _0.7 Al _0.3 As layer is not etched, etching can be accurately stopped at the surface of the p-Ga _0.7 Al _0.3 As layer. This structure
After performing shallow etching to improve the surface condition, MOCV again
It was filled with n-GaAs (3) by the D method. In the central part of the laser, the GaAs layer subjected to side etching serves as a mask for selective etching, so the sectional structure is as shown in Fig. 5 (a), and the current narrowing width is the laser end face shown in Fig. 5 (b). It becomes thinner than the area. Therefore, the gain guiding is the main guiding mechanism in the laser central region, but the refractive index guiding is the main guiding mechanism in the laser end face region. For this reason, the semiconductor laser of the present example has a similar optical output current characteristic with low aberration up to a high optical output and good linearity as in Examples 1 and 2, and also has good noise characteristics because it performs multimode oscillation. .

[Brief description of drawings]

FIG. 1 is a perspective view showing the basic shape of the structure of the first embodiment of the present invention, FIG. 2 is a view showing the sectional structure of a semiconductor laser of the first embodiment of the present invention, and FIG. 2 is a diagram showing a sectional structure of a semiconductor laser of Example 2, FIG. 4 is a diagram showing a mask shape of a second example of the present invention, and FIG. 5 is a sectional structure diagram of a semiconductor laser of a third example of the present invention. Is. FIG. 6 is a sectional structure of a conventional semiconductor laser. (1) ... p-GaAs substrate, (2) ... dent of GaAs substrate,
(3) ... n-GaAs layer, (4) ... stripe layer,
(5) ... p-Ga _0.5 Al _0.5 As cladding layer, (6) ... undoped Ga _0.86 Al _0.14 As active layer, (7) ... n-Ga _0.5 A
l _0.5 As cladding layer, (8) ... n-GaAs capping layer,
(9) …… AuGeNi / Cr / Au electrode, (10) …… Cr / Au electrode,
(11) …… n-GaAs substrate, (12) …… p-Ga _0.a Al _0.3 A
s, (13) …… Si ₃ N ₄ , (14) …… SiO ₂ , (15) …… p−
Ga _0.5 Al _0.5 As layer, (16) …… p-GaAs, (17) …… p ⁺ −
Ga _0.5 Al _0.5 As layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Satoshi Kajimura 1-280, Higashi Koikekubo, Kokubunji, Tokyo (56) References: Hitachi, Ltd. Central Research Laboratory (56)

Claims (1)

(57) [Claims] 1. At least a junction of semiconductors of different conductivity types for imparting an optical gain to a semiconductor medium and a stripe-shaped optical waveguide mechanism provided on the junction surface, the optical waveguide mechanism being a laser. In the central part, the gain difference between the inside and outside of the stripe is mainly used, in the vicinity of the laser end face, the difference in refractive index between the inside and outside of the stripe is mainly used, and the optical spot size in the laser end face region is A semiconductor laser device characterized in that a stripe width of a laser end face region is widened so as to be larger than an optical spot size.