JPS603181A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To reduce an adverse effect by the noise of returning beams, and to obtain a laser suitable for a light source for an optical disk by making the distribution width of the effective refractive index of a current stopping layer constituting a semiconductor laser device wider than that of gains. CONSTITUTION:An n type Ga0.55Al0.45 clad layer 12, an un-doped Ga0.85Al0.15As active layer 13 and a p type Ga0.55Al0.45As clad layer 14 are laminated on an n type GaAs substrate 11 and grown in a liquid phase in an epitaxial manner, and an n type Ga0.55Al0.45As current stopping layer 15 and an n type GaAs light absorption layer 16 from which striped sections are removed are laminated and formed on the layer 14. In the constitution, the band gap of the current stopping layer 15 positioned on the clad layer 14 is made larger than that of the active layer 13, and the refractive index of the light absorption layer 16 on the layer 15 is made larger than that of the current stopping layer 15. The refractive index of a p type Ga0.55Al0.45As coating layer 21 formed on the light absorption layer 16 is made smaller than that of the active layer 13.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a semiconductor laser device having both a gain waveguide structure and a refractive index≠wavepath structure.

[Technical background of the invention and its problems]

In recent years, semi-unit lasers using m-v group compound semiconductor materials such as GaAl and As-based semiconductor materials have been used for information processing of optical disk files such as DAI) and (digital audio disks). Application to four devices is currently underway. In semiconductor lasers for optical disks, it is necessary to narrow down the laser beam to a small size, so the optical system is
(2) From the point of view of simplicity, it is required that the astigmatism be small in the transverse mode oscillation. Furthermore, the following problems have been found when applied to optical discs. That is, in optical disc files, etc., information is read out by detecting the intensity of the reflected light that hits the disc.

It is inevitable that some of the reflected light will return to the semiconductor laser. Therefore, in addition to the resonator formed by both end faces of the laser, the semiconductor laser also has a resonator formed by the laser end face and the disk surface, making it a laser having a double resonator. And when the disk surface vibrates while rotating.

The latter resonator length changes, causing fluctuations in the spectrum, optical output, etc., and causing so-called return light noise.

Here, we will review the waveguide structure of a semiconductor laser from the perspective of suppressing return light noise.

Waveguide structures of semiconductor lasers are generally classified into two types: gain waveguide structures and refractive index waveguide structures. In these structures, there is a trade-off between reducing astigmatism and reducing sharpness noise. In other words, in the refractive index waveguide structure, astigmatism is 5 [
The longitudinal mode also oscillates in a single mode because the transverse mode is small (less than 1 µm) and stable, but the output fluctuation µ due to return light noise is larger than 7 % (1OC%) because the horizontal mode is narrow. On the other hand, in the gain waveguide structure, K ”- becomes larger. Therefore,
In order to simultaneously improve the characteristics of astigmatism and return light noise, the refractive index waveguide (^Y structure) and the gain waveguide structure must have the characteristics (a) of both structures.

By the way, a laser with a structure in which a current narrow Y drawing related to gain distribution and a refractive index waveguide structure are automatically formed is called a self-aligned laser.
A laser in which the groove structure does not appear on the crystal surface is called an internal stripe self-aligning laser. This type of laser is expected to have an easy manufacturing process and high commercial yield and productivity.
Because the active layer can be brought inside the crystal, it is less susceptible to defects from the electrode surface, the shadow of deterioration caused by the mount can be reduced9, and the contact resistance is reduced as a total electrode. It has the advantage that processes such as zinc diffusion can be omitted and that the surface can be made flat, which is advantageous for mounting.

As a conventional internal stripe self-aligned laser, VSIS (V -cl+ann
eled 8ubstrate InnerStrip
e) A laser is known, and it is known that this laser is mode-limited and has good return light characteristics. However, the V8I8 laser has a problem that it cannot be manufactured using the MO-CV method, which can be converted into the LPE method to grow crystals with good uniformity over a large area. Optical Disc Laser - This is a drawback for several semiconductor laser manufacturers, which have entered the era of production.

Therefore, we developed the 11th one-stripe self-aligned laser, which can be achieved by using the maximum aj1Mu-CVI) method.
゛As shown in <1, the active layer'' has an internal strave structure in the second part! 7. A closed laser was proposed. In the figure, I is an N-GaAs substrate, 2 is an N-GaAs substrate, /
, As clad layer, 3 is Ga AZ A 8 active layer, 4 is P-Ga As clad layer, 5 is N U
aA s'rfT, flow prevention layer, 6 is a striped groove, 7 is P-(J a AA A '' coating layer, 8
is a P-(jaAs coytact layer, and 9 and 1θ are metal electrodes. In this structure, the striped groove 6
The current blocking layer 5 in which the current blocking layer 5 is formed limits the current injection into the active layer 3 into a stripe pattern, and also causes the light guided in the active layer 3 to penetrate into the cladding layer 4 and the current blocking layer 5. As a result, a guided mode is formed directly below the stripe.

Therefore, a gain waveguide structure and a refractive index waveguide structure are simultaneously realized.

However, this divine laser had the following problems. That is, the widths of the gain distribution and the refractive index distribution are temporarily determined by the width of the striped grooves 6 of the current blocking layer 5, and the widths of each distribution are equal. In this case, the refractive index difference is sufficient. It becomes large and the characteristics of the gain waveguide cannot be seen. Therefore, the mode control effect is sufficient as a laser for optical disks.

Regarding the return light characteristics, it was not possible to obtain satisfactory results.

[Purpose of the invention]

An object of the present invention is to provide a semiconductor single-node laser which is extremely useful as a light source for optical disks and which can sufficiently reduce the adverse effects of return light noise without losing the characteristics of fundamental transverse mode oscillation and small astigmatism. The purpose is to provide 1111- equipment.

[Summary of the invention]

The structure of the present invention is as follows: in the structure shown in FIG.
(The aim is to further improve β1111 and make the width of the effective refractive index distribution wider than the width of the gain distribution.

That is, the present invention provides a semiconductor laser device made of compound semiconductor 1A material and having a double heterojunction structure,
A current 1 ([J, A stripe-shaped groove extending to the cladding layer is provided, and a groove is provided for light absorption having a higher refractive index than the cladding layer and the current blocking layer, and the above-mentioned groove of the absorption layer is provided with ME. (7: Provide a striped groove wider than 'f j'31Δ, and furthermore -
This is the same conductive type as Radova 4, and is provided with a coating 11 having a lower refractive index than the upper fl[2 active layer. - Due to the absorption ++V caused by 1, there is an effective refractive index difference between the stripe section and the BIS 3) of 1, and mode control is performed by the refractive index waveguide structure. In addition, the current limit tt-+v" due to q"
Current narrowing °Y (=Therefore, the injection of 75 current into the active layer is limited to a stripe shape, and in this case, the width of the light absorption stripe due to the absorption layer is larger than the current stripe width due to the current blocking layer) Since it is wide, the width of the gain distribution becomes narrower than the width of the effective refractive index distribution. Therefore, the features of the gain dedicated waveguide structure and the graded index waveguide structure are simultaneously achieved, and the adverse effects of return light noise can be sufficiently reduced without losing the feature of small astigmatism. .

According to experiments conducted by the present inventors, the laser with the structure of the present invention exhibits a refractive index waveguide structural characteristic of fundamental transverse mode oscillation at astigmatism of 110 (μtn 1 or less), while multimode oscillation occurs in the longitudinal mode. Output fluctuation meter due to return light noise is 1 [chi]
The gain waveguide structural characteristics are also shown below. The effect of this is that it has excellent transverse mode control and return light characteristics.

When considering the application to lasers for optical disks, etc., it becomes extremely large.

[Embodiments of the invention]

FIGS. 2(a) to 2(a) (the crests are j-plane views showing one culm of manufacturing a semiconductor laser device according to an embodiment of the present invention).

First, as shown in FIG. 2(a), <N-GaAR substrate IJ (
Si doped, n = 1~2 X l (1” c
m-3) (n = l x l U cm, + thickness 1.
5 ttm), 7y F-Ga AA As active layer 13 (1% 1 0.080, 85 0.14 I Itm), P-Ga Ae As cladding layer 14 (P
= l[)"~l O"cm, -', )jimiU
, 2 μm).

N −(-+ n A A A ” Current blocking h□j
J s (n ~ 0゜56 0,411 10 ~ 10 cm,, l?, mi 0.3 tt m)
and N'-QaA8 optical absorption IMJin=lO'8~I
O” cm-”.

0.5 μm thick) were successively grown. The MO-CV 1) method was used for the first crystal growth of this fabric, and the growth conditions were: temperature 750 [°C], V/ll-20, gear! J 7cas(H,)ノ3ij:;t ~i 0 [tb/mir+
], the raw material is trimethyl gallium (T MO: (CH
), ()a).

Trimethylaluminum ('rMA: ((',83)
, Ag).

Arsine (Asl-L, ), p dopant: diethylzinc (DEZ: (C,H5), Zn), n)'-panto: hydrogen selenide (11□Se), and the growth rate is 0.
25 (μnl/min).Although it is not necessarily necessary to use the I<, 10- CVD method in the first crystal growth, MO-, which allows crystal growth with good uniformity over a large area, Using the CVD method.

It is advantageous compared to the jyj combination L J) E method considering the mechanism.

Next, as shown in FIG. 2(b), a sootresin 77 is applied to the light absorption layer x6k, and the resist 17 is coated with a width of 3 [μm].
, a resin mask was formed by punching in stripes with a pitch of 3 (10 Cμm). Subsequently, a phosphoric acid-based etchant (warm temperature 20° C.) was applied once a month, and the light absorption layer 16 and i'i, flow 1 11 stop layer I
5 for about 40 seconds until reaching the crat layer 14.1. Ta. Next.

Only the light absorbing layer I6 was etched using L' ty etch-Vant.
As shown in Figure 2 FC+, 0.5 on both sides (p Ill
) for about 1 () seconds. At this time, the crossroad fl'17'r varnish drive width is Ii! ,
7Af, l! 11 Stop layer 15 W+-2C in 13 minutes
rt Ill), vv in the portion of the light absorbing layer 16 for 5 minutes.

= 4C71m] Next, the resist 17 was removed, and after t4 cleaning and HCA treatment to remove surface oxides, the sample was immediately placed in a furnace and the second crystal growth was performed. O-CV I)
I went by law. That is, the 21'<((as shown in 11, P-()aAAA80-5 0.48 applied layer 27 (t)=lOcm+thickness 1.2 μm on the entire surface).

P-UaAs coytact layer, l'2 (p=lOcrn
.

A thickness of 211 Ill) was sequentially grown. At this time, is the crud I fogging out? This is because both J J 4 and the current blocking layer 15 have an A 4 concentration of 0.45.

It cannot be grown using the LPE method, and the MO-CVI method or M
BE method (molecular beam epitaxial method) is required.

Next, a Cr-Au layer 23 was formed as a P-side electrode, and an Au-Oc layer 24 was formed as an IN-side electrode. By cleaving this sample, a resonator with a length of 250 [μm] and a width of 3
(A semiconductor laser was completed with a chip of 10 (μrn:).

When the characteristics of the thus produced laser were measured, the following first-order results were obtained. t, that is, the oscillation threshold is 7
0(InA), lower, non-aperture, aberration is 1(BμITI
'3 or less, I will start the Itogi horizontal mode, 5Cm W:]
Until now, the output fluctuation due to the acid multimode oscillation C1 return light noise was less than 1 [ch]. This characteristic is sufficient for use as a laser for optical disks! This is within the range of 1llfj.

As described above, according to this embodiment, astigmatism can be sufficiently reduced by Isamoto transverse mode oscillation.

In addition, the force due to the return light noise can be made sufficiently small. Therefore, it is extremely difficult to use as a light source for optical disks. Also.

Since it can be formed by the MO-CV L) method, it is extremely effective in producing human eyes. Furthermore, since the light absorption layer 16 is of the same conductivity type (N type) as the current blocking layer 15, there are advantages such as more reliable narrowing of the current.

Note that the present invention is not limited to the embodiments described above. For example, the growth method for each layer is M (J −CV
The method is not limited to the D method, and may be the Ivi BE method. Further, the composition ratio of each layer is not limited to the embodiment, and can be changed as appropriate depending on the specifications. For example, it is also possible to set the A1 composition of the cladding layer to 0.35 to obtain a high-output laser that has the effect of functioning as a light guide layer.

Furthermore, instead of GaA/4As-based materials, C1aln
It is also possible to use a P-jGaAAA8P-based compound semiconductor material. Further, the conductivity type of the light absorption layer is not limited to N type, and may be P type without any problem. Furthermore, it is also possible to use a P-type substrate instead of an N-type substrate 7 and reverse the conductivity type of each layer.In addition, various modifications may be made without departing from the gist of the present invention. It can be implemented by

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a sectional view showing the schematic structure of a conventional internal stripe self-aligned laser, and FIG. It is a sectional view showing a process. 11-N- (JaAs substrate. Jx-=N-Gaie As cladding layer, O40
0,45 13...Undoped tJ a A -1=A s active layer, 0.85 0. is 14---P-Ga A, #As cladding layer, (1,
5! I O,4B 15-N-(la A,I!-As current blocking layer. 0, Sfi O,4!1 16-N-GaAs light absorption layer, z Z-P-Oa Ae As coating layer, 22.・・P-
GaA8 contact layer. Applicant's representative Patent attorney Takehiko Suzue Figure 1] 0 Figure 2 (a) 6 Figure 2

Claims (2)

[Claims] (1) In a semiconductor single-input laser device that is made of a compound semiconductor material and has a double heterojunction, a cladding layer with a refractive index smaller than that of the active layer is grown on the side of the active layer opposite to the substrate. The cladding layer is grown on this cladding layer, and has a stripe-shaped groove portion having a length opposite to that of the cladding layer in which the striped 11h portion is formed, and is wider than the groove portion on one groove portion. The formed cladding layer and / 1. A semiconductor laser device comprising: a coating layer having a refractive index smaller than active 1·η. (2) The semiconductor laser device according to claim 1, wherein the light absorption layer has the same conductivity type as the 11J current blocking layer.