JPS63307793A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser element, which has low threshold currents and no astigmatism and in which no higher transverse mode is generated, by forming a region blocking a diffusion to both sides of a stripe of carriers in an active layer so that its width is the same as or narrower than a that of channel. CONSTITUTION:A region blocking the diffusion of carriers in an active region 3 is formed into an optical guide shaped by absorbing light from the active layer 3 on both shoulders of a striped groove 7 formed onto a substrate 1, and the width Wm of the region is set at a value the same as or narrower than the width Wc of the optical guide approx imately. Accordingly, since the width Wm of the active layer is shaped dn width narrower than or the same as the width Wc of a V channel and both sides of a mesa-shaped region including the active layer 3 are buried with multilayer crystal layers 11, 12, leakage currents are reduced, and currents can be concentrated effectively into the narrow mesa-shaped region, thus acquiring a semiconductor laser oscillating at an extremely low threshold. Characteristics having no astigmatism are obtained with excellent reproducibility.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an element structure of a refractive index waveguide semiconductor laser having an extremely low threshold current and no astigmatism.

<Prior Art> When conventional semiconductor laser devices are classified by optical waveguide mechanism, they are classified into gain waveguide type and refractive index waveguide type.

However, from the point of view of transverse mode stability, which is important for applications, the refractive index guided laser is more advantageous in terms of insulation, and index guided lasers with various structures have been proposed. A typical example of this is
B H (Buried Heterostruc
) laser and VSIS (V-channel
ed 5ubstrateInner 5tripe)
There's a laser.

FIG. 3 is a schematic cross-sectional view showing the element structure of a BH laser. A striped multilayer crystal structure portion having a width Wm is formed on the p-GaAs substrate 1, and this portion becomes an operating portion for laser oscillation. That is, this multilayer crystal structure is p-GaAtA
s cladding layer 2, GaAtAs active layer 3, n-Ga
It constitutes a double heterojunction structure consisting of an AtAs cladding layer 4 and an n-GaAS cap layer 5. ! Since both sides of the active layer 3 are filled with a low refractive index material 15, it exhibits perfect refractive index waveguide, has no astigmatism, and has the advantage of having a relatively small threshold current of about IOmA. However, unless the refractive index of the buried layer 15 and the waveguide width W are appropriately selected m, oscillation is likely to occur in a high-order transverse mode, so there is a drawback that there are many restrictions in terms of manufacturing conditions.

On the other hand, the vsts laser shown in FIG. 4 has a width Wc after depositing an n-GaAs current blocking layer 6 on a p-GaAs substrate l.
After cutting a striped V-shaped groove to open a current path from the substrate 1 with the current blocking layer 6 removed, p GaA
tAs cladding layer 2, GaAtAs active layer 3, n −
A double heterojunction laser operating section is formed by sequentially laminating a GaAtAs cladding layer 4 and an n-GaAs cap layer 5, and even if the waveguide width Wct is as wide as Wct-4 to 7 μm, the waveguide cannot be guided within the active layer 3. Light outside the wave path passes through the current blocking layer (
6) and is absorbed by the substrate 1, which has the advantage that higher-order mode gain is suppressed and higher-order transverse modes do not occur. However, when the threshold current is 40 to 60 mA, fiB
It has drawbacks such as being expensive compared to the H laser and having a relatively large astigmatism of 10 to 20 μm. The reason for the high threshold current is that while the current is confined by the internal stripe structure of the current blocking layer 6, carriers injected into the active layer 3 diffuse to both sides of the active layer 3 in the lateral direction. ,
This is because carriers that are invalid for laser oscillation are generated. These invalid carriers are consumed by unnecessary spontaneous emission and heat generation, which adversely affects the reliability of the laser device. Also, vs.
The large astigmatism of the IS laser occurs because light on both sides of the waveguide is absorbed, and the wavefront of that light lags behind the center.

<Objective of the Invention> The present invention solves the problems of the above-mentioned BH laser and VSIS laser, and provides a semiconductor laser device with a low threshold current, no astigmatism, and no generation of higher-order transverse modes. The purpose is to

In order to achieve the above object, the present invention is characterized in that a VSIS laser is provided in which a region that prevents carriers in the active layer from diffusing to both sides of the stripe is formed to have a width equal to or narrower than the channel width.

<Example> The first recessed hole or FIG. 1(C) is a schematic diagram of a semiconductor laser showing each example of the present invention. Hereinafter, a first embodiment of the present invention will be described with reference to the first recessed hole. p-type G
V channel groove 7 of VSIS laser using aAs substrate 1
Mesa etching is performed from the surface of the chap layer 50 to the n-GaAs current blocking layer 6 on both sides of the channel groove width Wc=
The mesa width at one active layer 3 is set to 4 μm and Wm is 2 μm, and the mesa width is formed so that Wm is smaller than Wc. Next, high-resistivity AtxGa was grown by liquid phase epitaxial (LPE) growth method.
I-XAS (0,5<x, non-doped or Ge-doped) first buried layer l 1 , p-AtxGa+-XAS
(x=0.2) second buried layer I2 and n-At
A third buried layer 13 of xGa+ -XAS (x==0.2) and a fourth buried layer (cap layer) 14 of n-GaAs are sequentially grown. At this time, the first buried layer 11 and the second buried layer 12 are adjusted so that they do not grow on the surface of the cap layer 5 by shortening their growth time. The third buried layer 13 is grown after the second buried layer 12 is grown to improve the flatness of the element surface, and regardless of the thickness of the fourth buried layer 14, the element surface is sufficiently covered. It became flat.

The semiconductor laser device according to the first embodiment shown in FIG. 1(5) is made of AtGa
By forming a Pn reverse bias junction formed by the AS first buried layer 11 or the p-AtGaAs second buried layer I2 and the n2-GaAs current blocking layer 6, the leakage current can be extremely reduced. A value current of around IOmA and an oscillation wavelength of 780 nm were obtained. Furthermore, in CW (continuous wave) operation, it was possible to oscillate in a stable fundamental transverse mode up to an optical output of about 20 mW.

The reason why the fundamental transverse mode is maintained up to such high power is that
The active layer width (Wm=2μm) is the V channel width (Wc='4
Although the width is narrower than .mu.m), it is thought that this is because the light seeping out from the active layer is absorbed by the shoulder of the V channel, and the effect of suppressing the gain of higher-order modes remains. Also, the mesa width Wm is V
Since the channel width is narrower than Wc, the amount of light absorbed by the substrate is reduced compared to the conventional VSIS laser shown in Fig. 4, approaching a perfect index-guided type BH laser shown in Fig. 3. Figure 1(B) shows the mesa etching adjusted to match the channel width (Wc 24 .mu.m) and the active layer width (Wm 24 .mu.m). The buried semiconductor laser in this example also has a threshold current of around 15 mA and an oscillation wavelength of 780 nm.
m was obtained with good reproducibility. It was also confirmed that in the Wc operation, oscillation was performed in the fundamental transverse mode up to an optical output of 20 mW or more. The beam waist of the laser beam coincided with the end surface, and there was no astigmatism.

The third embodiment shown in FIG. 1 (Q) is different from the first embodiment shown in the first recessed hole.
The only difference is that the base substrate for growth is a GaAs substrate 1 on which an n-GaAS current blocking layer 6 is formed. By using such a substrate, the channel groove 7
Since the current blocking layer 6 can be sufficiently thick outside, it is possible to prevent the current blocking layer 6 from being etched and become too thin during mesa etching, and this has the effect of suppressing the generation of leakage current. There is. Therefore, the yield of devices can be further improved.

In the third embodiment shown in FIG. 1(C), the oscillation threshold π current 1th and the mesa width when the mesa width (active layer width) Wm is set below the V channel width (Wo=4 μm) Wm
The relationship is shown within the rectangle 0ABC in FIG. Also, for comparison, the relationship between Ith and wm of the conventional buried-VSIS (B-VSIS) V-za shown in FIG. 5, where the mesa width Wm is wider than the V channel width Wc, is also outside the rectangle 0ABC in FIG. It is shown in The smaller Wm is, the smaller 1th becomes, especially when Wm≦WC (within rectangle 0ABC) 1th is 15
It can be seen that by making the mesa width Wm smaller than the V channel width WC, an even lower threshold value can be achieved compared to the conventional B-VSIS laser. Also, even if Wm is reduced to 2 μm or less, it will decrease from 2 μm to 4 μm.
It was confirmed that it oscillated in the fundamental transverse mode up to 20 mW or more even in the range of μm, and that there was no astigmatism.

When Wm is 2 μm, the refractive index optical waveguide itself satisfies the fundamental transverse mode oscillation condition even if there is no light absorption effect on the GaAS substrate.

<Effects of the Invention> As described above, according to the present invention, the active layer width is formed to be narrower than or equal to the V channel width, and both sides of the mesa-shaped region including the active layer are coated with high resistance AtxGal-XAS(0 ，
By embedding it with a multilayer crystal layer including a Pn reverse bias junction of Azxca 1-XAS (5< Therefore, a semiconductor laser that oscillates at an extremely low threshold value can be obtained. In addition, in the semiconductor laser formed in this way, although the mesa-shaped region exists inside the V channel, the effect that light seeping out from the active layer into the buried layer is absorbed by the shoulder part of the V channel is maintained. Maybe because there is, 2
It fired in the horizontal fundamental mode up to a high output of 0m1V or more, and showed characteristics with no astigmatism with good reproducibility.

Note that the semiconductor laser device of the present invention has the above-mentioned G a A
Without being limited to the s -A&;aAs system,
It can also be applied to npInGaAsP-based and other heterojunction laser elements. In addition to the LPE (liquid crystal epitaxial growth) method, the growth methods include MO (organic) -CVD method, V
PE (vapor phase epitaxy) method and MBE (molecular beam epitaxial)
You may also use the law.

[Brief explanation of the drawing]

FIGS. 1A, 1B, and 1C are schematic diagrams showing each embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a conventional BH laser. 3 to 5 are schematic cross-sectional views of conventional VSIS lasers. 1: p-GaAs substrate, 2: p-AtGaA
s cladding layer 3: AjGaAs active layer, 4:
n-AtGaAs cladding layer 5: n-GaAs cap layer, 6: n-GaAsT flow blocking layer, 7: v-channel groove, 8, 9: electrode 1! = high resistance A
tGaAs first buried layer, +2: p-AtGaAs
2nd buried layer, +3: n-AtGaAs third buried layer, +4 2n-GaAs cap layer, 15: Kajikomi layer

Claims (1)

[Claims] 1. Inside the optical waveguide, which is created by absorbing light from the active layer on both shoulders of a striped groove formed on the substrate, a region is formed to prevent diffusion of carriers in the active layer. A semiconductor laser device characterized in that the width of the region is set to be approximately the same as or narrower than the width of the optical waveguide. 2. The region for preventing carrier diffusion is embedded in a multilayer crystal layer including at least one of a high resistance compound semiconductor layer or a multilayer including a Pn reverse bias junction of a semiconductor layer. The semiconductor laser device described above.