JPS60245189A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To generate a laser light having no astigmatism by setting the refractive indexes of inside and outside of narrow groove of a double hetero junction, refractive ratio to the prescribed values and oscillating in stable basic mode to high output. CONSTITUTION:An N type GaAs current blocking layer 12 is laminated on a P type GaAs substrate 11, 2-stage channel 21 of wide width groove 19 and V- shaped narrow width groove 20 are formed by etching, and a P type GaAlAs clad layer 13, a P type GaAlAs active layer 14, an N type GaAlAs clad layer 15, and N type GaAs gap layer in a double hetero configuration are laminated. The real number section of the double refractive index difference of the inside and outside of the groove 20 is 4X10<-3> or larger, and the conjugate section is 4X10<-3> or lower. Then, the mode is stabilized without influence of the variation in the carrier distribution, and when the ratio of the real number section and the conjugate section is set to 1.5 or higher, a beam waist falls without the ultafine distance from the end. As a result, stable basic mode oscillation occurs to high output, and a laser light having no astigmatism that the beam waists coincide at the end is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a semiconductor laser device whose oscillation transverse mode is controlled and which is free from astigmatism.

Conventional technology> Conventional semiconductor laser devices can be classified based on the optical waveguide mechanism.
It is divided into gain waveguide type and refractive index waveguide type.

In the former gain waveform, the transverse mode is unstable, and the astigmatism is large within 30 μm from the beam waist position where the optical beam width is minimum in the direction parallel and perpendicular to the junction. Therefore, there are some inconveniences in terms of application.

The latter refractive index waveform has the advantage of stable transverse mode and small astigmatism. Typical examples of index-guided semiconductor lasers include buried lasers and VST
S (V-channel led Sul) 5
There is a trateTnner Stripe) laser.

A buried laser has an active layer buried in a low refractive index material, so it exhibits perfect refractive index waveguide and has a threshold current of 1 t.
It has the advantage of having a small h, oscillating in the fundamental transverse mode, and having no astigmatism. On the other hand, it is unsuitable for Takabatake lasers because it has the drawbacks that high-order transverse modes occur at relatively low optical output and the end faces are easily destroyed.

GaAs-(,1aA(9As VS
In the IS laser, light is guided by the effective refractive index difference ΔN and the loss difference Δα of the active layer 4 between the inside and outside of the \l-channel 9. Therefore, even if the threshold current Ith is higher than that of a buried laser, or the effective refractive index difference ΔN is sufficiently large, the current blocking layer 2 absorbs light in higher-order modes outside the channel. , it has the advantage of maintaining the basic transverse mode up to high output. When the effective refractive index difference ΔN is increased, the loss difference Δα also increases at the same time.

For example, Δα of a conventional VSIS laser is ] ('l (l
r) ~ 2 (100cm''''.) - If the loss outside the channel is large, the phase of the light there will be delayed, and the beam waist will easily penetrate deeper than the end face.For this reason, the conventional VSIS laser had the disadvantage that the beam waist in the direction parallel to the joint went 5 to 15 microns deep from the end face.

<Objective of the Invention> An object of the present invention is to provide a semiconductor laser which oscillates in a stable fundamental transverse mode up to high output and whose beam waist coincides with the end facet, that is, there is no astigmatism.

<Structure and operation of the invention> The semiconductor laser device of the invention will be described with reference to FIG.

After depositing an n-GaAs current blocking layer 12 on the p-GaAs substrate 11'' to provide a current blocking function to the +1-GaAs substrate 11, a current 3f1. A wide groove 19 having a width II+1 and a depth D is formed from the surface of the first layer 12 by etching. Next, in the center of the groove 19, the maximum width -\7
The groove 20 is formed by etching. In this way, a p-GaA7As cladding layer 13, a p-GaA(7
As active layer 14, n-GaApAs cladding layer 15, n
A double heterostructure consisting of a GaAs cap layer 16 is laminated.

Here, the real part Re (ΔTakara) and the imaginary part L+ (ΔRyo) of the complex refractive index difference Δ1 between the inside and outside of the \1-shaped groove 20 are the active layer thickness d2 and the 1)-cladding layer in the groove 19. Figure 2 shows the results of calculating how the thickness changes depending on the thickness d1f. Further, Re (Δπ) and Im (ΔW) are expressed by the following equations.

Re(Δa)=ΔN (1) 1m(ΔW) =Δcr/2k (2)-3= However, ΔN is the effective refractive index difference, Δα is the loss difference outside the \I-channel, and the wave number (2π /λ). Second
The figure shows the case of wavelength λ near 8 (l nn+. From this figure, Re(Δ1)(ΔN) and Lm(Δ
It can be seen that π)(Δα) decreases as dl, - and d2 become thicker.

The built-in effective refractive index difference ΔN and loss difference Δα described above
In addition, it is necessary to take into account changes in the refractive index due to carriers injected into the active layer 14. When the optical output is increased, carrier distribution changes due to spatial hole burning, etc.
The refractive index distribution also changes, causing disturbance of transverse modes. The variation is about 3×10 −3 .

Therefore, in order to stabilize the transverse mode, it is necessary to make the built-in effective refractive index difference ΔN sufficiently large so that it is not affected by carrier distribution fluctuations. Traditional VSIS
For the laser, the active layer thickness d2 = 0.1μ, the grad thickness d,
Since f=0.15μIII, ΔN=1.5X10
-2, which is sufficiently large, but the absorption outside the ■-channel is Δα
=2000゜m-1=4-, which is too thick.

If this Δα is too large, the phase of the light will be delayed and the beam waist will tend to penetrate deeper than the end face. On top of that,
The differential quantum efficiency also decreases to 15% or less.

For the reasons stated above, ΔN is as large as deviates from Δα
There should be an active layer thickness d2 and a p-cladding layer thickness d, flll that are as small as possible. Therefore,
The ratio of Re(Δ1) to 1m(ΔW) was defined as a parameter R, and how it depended on d2 and dlfu+ was investigated by calculation.

R=Re(ΔN)/rm(Δ1lf) (3) FIG. 3 shows the d2 dependence of the R parameter, and FIG. 40 shows the "fw dependence" of the R parameter.

From these figures, the R parameter largely depends on a2, and d
It was found that there is almost no dependence on 1fu+.

Therefore, the present inventors investigated samples with various active layer thicknesses d2 with a distance of 3 from the end face of the beam waist.
When Re (ΔR) and ■111 (ΔD) were calculated for those located within μm and those located deeper than 3 μm, the results shown in FIG. 5 were obtained.

In Figure 5, the circle mark indicates that the beam waist is 3 μm from the end surface.
The X mark indicates the case where the beam waist is deeper than 3 μIll from the end face.

As is clear from Fig. 5 above, in order for the beam waist to be within 3 μ'0 from the end face, Re
≧4X10-3. Im(at Δ)≦4X1('l-3゜R
It can be seen that it is sufficient if ≧1.5.

It has been found that by satisfying the above conditions, it is possible to realize a semiconductor laser with a stable transverse mode up to high output and no astigmatism. Therefore, it is better for the active layer thickness d2 to be thin as long as Itb does not increase, and 1] - cladding layer thickness d1. If so, it is better to increase the thickness until the above conditions are satisfied.

Another advantage of the semiconductor laser of the present invention is that the conventional
While the SIS laser determines the transverse mode using a single-stage refractive index/loss distribution, the transverse mode is fixed using a two-stage refractive index/loss distribution, so even in high-power operation, it is difficult to detect peak shifts. This is something that cannot be done.

The laser of the present invention is also excellent in terms of layer thickness control of the cladding layer thickness "fiu".Why is the depth of the width groove 19 3D
Since it is formed by etching, it is uniform over the entire surface of the substrate, and the p-cladding layer d11 outside the wide groove 1≦J formed by the liquid phase epitaxial method has a uniform layer thickness within the plane up to about 0.15 μm0. It is. Therefore, d
, fllI=D+d, r is almost uniform within the plane.

If 0.3 μt.

If the thickness of
and tends to become uneven. This laser is B5l5 laser' (
Broad-channeled 5ul)str
at, e Inner Stripe 1aser).

<Example> An example of the semiconductor laser device of the present invention will be described using a GaAs-(-, 1aA(4As-based compound semiconductor).

7- As shown in FIG. 1, (10
0) N-type GaAs current blocking layer 12 with a thickness of 0.8 μm on the surface
Grooves 19 having a width of 6.5 .mu.m and a depth of 0.2 .mu.m were formed from the surface thereof by photolithography and chemical etching. Next, the width u+2=3.5μ is placed in the center of the groove 19.
The m-shaped groove 20 was etched to reach the p-GaAs substrate 11. On the substrate with the two-stage channel formed in this way, p Ga□, 5 A lo,
5As cladding layer 13, '-GaO, 85Aj6.15
As active layer 14, n-(xa□, 5 A16.5As
A double heterostructure consisting of a cladding layer 15 and an n-GaAs cap layer 16 was grown by liquid phase epitaxial growth. The layer thicknesses are: d+r = 0, 1 μm, d+f, = 0.3
μm, a2 = 0.06 μm. At this time, R parameters determined by calculation, ΔN and Δα
are 2°8 x 10-'' and 650 cm', respectively.

Next, after lapping the back surface of the substrate to make the thickness of the semiconductor laser device approximately 100 μm, Au-Ge-Ni was deposited on the surface of the 8-n-Ga As cap layer 16 as an n-side electrode. , A11-Zn is deposited on the back surface of the semiconductor laser element 11 as an n-side electrode,
Alloyed by heating to 450'C. Thereafter, folds were formed so that the resonator length was 250 μIl+.

As described above, the method for manufacturing the B5l5 laser' of the present invention is easy. The B5l5 laser of this example has a threshold current I
th=45+nA, oscillates at oscillation wavelength λ=7'80,
Most of the elements operated in a stable fundamental transverse mode up to a light emission output of 4.0 mW, and no peak shift was observed in either the near-field or far-field images. Furthermore, the beam waist coincided with the end face up to 40 mW both in the direction parallel to and perpendicular to the junction. The differential quantum efficiency was 25% on one side.

FIG. 6 is a cross-sectional view of the embodiment shown in FIG. 1 when grooves are formed by RIE (reactive ion etching). Compared to grooves formed by chemical etching, this type is characterized by the fact that the groove sides do not have a taper. The B5l5 laser manufactured using this RIE also showed almost the same characteristics as the previous example.

<Effects of the Invention> Hereinafter, the semiconductor laser (BSI) of the present invention will be described.
S laser) has a two-stage refractive index/loss distribution with a two-stage channel, and optimization of R parameters, ΔN, and Δα by controlling the active layer thickness and 1)-cladding layer thickness, resulting in stable transverse mode up to high output power. , stigmatism can be achieved.

Note that the semiconductor laser device of the present invention is made of the above-mentioned GaAs
- Not limited to GaAs substrate system, but InF'-InGaA
It can be applied to sP-based and other heterojunction laser elements. In addition, the growth method is liquid phase epitaxial (LP)
E) Not limited to the method, M O-CVD method, VPE method, M
This can be avoided by applying the BE method, etc.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of the B5l5 laser of the present invention. Figure 2 shows the complex refractive index difference Δγ, the real part Re (Qn), and the imaginary part Im (6M) (1) - cladding layer thickness d, fw, d2
A graph showing dependencies. FIG. 3 is a graph showing the dependence of the R parameter on the active layer thickness d. Fig. 1 is a graph showing the dependence of the R parameter on the p-cladding layer thickness fw. Fig. 5 is an explanatory diagram of the optimum ranges of Re (Δ'ii), Tm (Δ'i'i), and R harammeter. Fig. 6 is a sectional view of an embodiment of the pond of the present invention. Fig. 7 is a sectional view of a conventional \7SIS laser. 1] r 21--1l-GaAs substrate. 12, 22-- n- GaAs current stop layer. 13, 23...T-GaA, (JA
s cladding layer. 14,24·=-p-GaA f As active layer. ] 5, 25...-n-GaA, (J, A
s cladding layer. 16.26...-n-GaAs cap layer! 17.27
...11 side electrode. 18.28... side electrode. 19.29...@town, ditch with depth D. 2rl, 30... Ditch with width and width. Patent Applicant Sharp Co., Ltd. Agent Patent Attorney Aoyo 2 people

Claims (1)

[Claims] (1) A channel having two groove widths, wide and narrow, is formed on the substrate, and a double heterojunction structure is formed at least in the channel portion, and the inner and outer sides of the narrow groove of the double heterojunction are formed. The real part R, e (Δy) of the complex refractive index difference Δγ is 4X10-3 or more, and the imaginary part Im (Δ″iV) is 4.
X 1 (1-3 or less, the ratio Re(Δ, n)/
A semiconductor laser device characterized in that T m (6M) is 1.5 or more.