JPS59227177A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain stabilized transverse mode oscillations by a method wherein, when a clad layer, an active layer, an optical guide layer and a clad layer are laminatedly grown on a semiconductor substrate, these layers are formed into a mesa form and a semiconductor laser is constituted by surrounding these layers with a layer having a forbidden band width wider than that of the active layer and having a smaller refractive index than that, the thickness of the clad layer adjacent to the optical guide layer is set at 0.1mum or less and at the same time, a layer, which has a light absorption function, is provided thereon. CONSTITUTION:An N type Ga0.70Al0.30As clad layer 2, an undoped Ga0.86Al0.14As active layer 3, an N type Ga0.74Al0.26As optical guide layer 4, a P type Ga0.55Al0.45 clad layer 5 of a thickness of 0.1mum or less and a P type Ga0.88Al0.20As layer 6 having a function of light absorption are laminatedly grown on an N type GaAs substrate 1. Then, these layers are processed in a mesa form and surrounded with a P type Ga0.55Al0.45As buried layer 7 provided in the surface layer part of the substrate 1 and an N type Ga0.55Al0.45As buried layer 8, which is located on the buried layer 7 and has a forbidden band width wider than that of the layer 3, and at the same time, has a smaller refractive index.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to the structure of a semiconductor laser with high output and stable transverse mode.

[Background of the invention]

In LOC type lasers such as the conventional BH type laser with a light guide layer (the structure shown in Figure 1) and the 8BH type laser (the structure shown in Figure 2), the cladding layer adjacent to the light guide layer is thick ( 1 μm or more), the higher-order mode in the direction perpendicular to the junction suffered only the same level of loss as the fundamental mode, and there was a problem in mode selectivity.

[Purpose of the invention]

An object of the present invention is to provide a high-power semiconductor laser whose transverse mode is stable.

[Summary of the invention]

In order to achieve the above object, the semiconductor laser device of the present invention has an optical guide layer adjacent to an active layer, and at least one optical guide layer having a larger forbidden band width and a lower refractive index than the active layer on the side of the mesa stripe. In a layer-embedded semiconductor laser device, if the thickness of the cladding layer adjacent to the optical guide layer is less than 1.0 μm, it is acceptable to have a semiconductor layer adjacent to the cladding layer with a narrower band gap than the active layer. Features.

Conventional BH type laser with optical guide layer (@Figure 1) [N, C
hinone et, al, Appl, phys,]
[, ett, 35(7).

No. 513], the thickness of the cladding layer adjacent to the optical guide layer was 1 μm, and the proportion of transverse higher-order modes perpendicular to the junction leaking into the substrate was small. Also, the 18BH type laser (Fig. 2) ()i, Blauvelt et.

al, , , 4ppl, phys, Lett, 41 (
51,485), the thickness of the cladding layer adjacent to the optical guide layer is also 1 μm, and since there is no semiconductor layer with high optical absorption adjacent to the cladding, the above-mentioned optical absorption loss in the higher-order mode can be fully expected. could not. Therefore, in a laser with such a LOC structure, the refractive index of the cladding layer adjacent to the active layer is made larger than that of the cladding layer adjacent to the light guide layer, and the cladding layer adjacent to the cladding layer with the smaller refractive index is Then, a light absorbing semiconductor layer is provided. At this time, the thickness of the cladding layer sandwiched between the light guide layer and the light absorption semiconductor layer is controlled in order to increase the light absorption loss by the same absorption semiconductor layer in the higher mode and increase the loss difference from the fundamental mode. It is necessary. Figure 3 shows, from the left of the figure, A
tA3 cladding layer with mixed crystal ratio U = 0.45, active layer (thickness 0.084 m) with X = 014, light guide layer (thickness 0.8 μm) with Y = 0.26, Z = 0.30 This figure shows the relative light intensity distribution of the TE mode and the T E t mode calculated by the equivalent refractive index near-polarization for the four-layer slab waveguide which is the cladding layer. Also, in FIG. 4, the active layer thickness is 0.15μ in FIG. 3! It is a figure when it changes to n. From Figures 3 and 4, it can be seen that if the thickness of the cladding layer adjacent to the optical guide layer is less than 1.0 μm, the loss in high modes due to the light absorption semiconductor layer adjacent to the cladding layer increases. .

FIG. 5 is a diagram in which a light-absorbing semiconductor layer is added as a cap layer to the conventional 18BH structure (FIG. 2).

Further, FIG. 6 is a cross-sectional view of an SBH type laser in which the conductivity type of the light guide layer is n type, and a substrate is used as a light absorption semiconductor layer. In both FIGS. 5 and 6, the thickness of the cladding layer between the light guide layer and the light absorption semiconductor layer is less than 1.0 μm.

Note that by making the difference in refractive index of the cladding layer large and less than the value te, de, which is the thickness t of the optical guide layer and the thickness di-I of the active layer, higher-order modes in the vertical direction can be cut off. However, according to the present invention, the spot size (
This refers to the spread of light within the layer.The larger the value, the higher the optical output can be obtained. This means that it is possible to simultaneously improve device characteristics and suppress higher-order modes.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 7, 8, and 9.

Example 1 FIG. 7 shows the GRAtAS system S B I- according to the present invention.
1 is a cross-sectional view showing a method for manufacturing a type 1 laser.

As shown in FIG. 2(a), n-GaAs is grown on an n-GaAs substrate 1 by a liquid phase epitaxial growth method.
o A4. mA8 clad #2,” Gao, y4
Ato, ts A S Light guide layer 3. Undoped G'
o, ssAm, 14 AS active layer 4. P(3”o,ss
Ato, 4s As cladding layer 5. Workmanship P-G
ao, so At6. ! @A S The cap layer 6 is grown sequentially. Next, mesa stripes are formed by etching as shown in Φ) in the same figure. In this mesa formation,
The depth of the mesa is set at QaA to facilitate subsequent buried growth.
It is necessary to reach the s-substrate.

In an SBH type laser, the width of the optical guide layer must be wider than the width of the active layer in the direction perpendicular to the stripe, and in this example, the p-cladding layer is etched by selective etching as shown in FIG. Gap, □A/4.4 SAS only was etched by about 1 to 3 μm from both sides.

Here, HF was used as the selective etching solution.

Thereafter, the active layer exposed on the side surface of the assist live by this selective etching was removed using an ISPO4 etchant to form a cross-sectional structure as shown in FIG. 4(d). Next, as shown in the figure (e), mesa stripes were formed by liquid phase epitaxial growth. p, 1s
A8 layer 7 and "G ao, ss Ato, as
Filled with As layer 8. Since the bias is reversed outside the stripe region, the current flows only in the stripe region. This buried layer is Gao, ss Ato, is
An As high resistance layer may also be used. FIG. 5(f) is a final cross-sectional view of the device, in which ohmic electrodes 10 and 11 are formed after selective diffusion 9 or full-surface diffusion of ZN.

According to this example, it was possible to obtain an element that oscillates in the fundamental transverse mode up to an optical output of 30 to 50 mWcW at an oscillation wavelength of 0.78 μm and a stripe width of 3 to 5 with good reproducibility.

In addition, as shown in Table 1, as a result of fabricating devices in which the n-cladding layer thickness was varied from 0.8 μm to 1.5 μm, the results were 1.0 μm.
In the device smaller than μm, the transverse mode in the vertical direction was a stable fundamental mode.

Example 2 FIG. 8 shows the semiconductor laser device of Example 1 manufactured by MO-CVD or MBE instead of liquid phase growth, and the active layer is made into a quantum well type. As shown in the figure, the features of this embodiment include the structure of the active layer 4;
Thickness ~120 GaoeoA M-1OA8 quantum wells in 3 layers, thickness ~30A Ga5-o5 Ato, 3@A
A multilayer quantum well type (Mu
l tiple Quantum we J l ;M
QW) active layer. In this example, the oscillation wavelength is 0.7
A device with a thickness of 6 to 0.80 μm, a fundamental transverse mode up to an optical output of 100 mW, and a low threshold current (30 mA or less) was obtained.

Embodiment 3 FIG. 9 shows a cross-sectional structure in the laser optical axis direction of the semiconductor laser device of Embodiment 1 or Embodiment fII2, in which the end face is made transparent to laser light. The light guide layer 3 exists up to the laser beam reflecting end face, and the end face of the active layer 4 is arranged inside the reflecting end face. After forming the mesa stripes shown in FIG. 7(d),
Only the p-Gao, so, Ato4o As cap M 6 , p()ao, 5sA-/a, n5A8 cladding layer 5 and active layer 4 at the end face portion are removed by selective etching. Thereafter, the outside of the stripe was buried with a GaA3 substrate layer in the same way as the buried growth in Example 1.

In this example, in the structure of Example 1 with transparent end faces, a visible semiconductor laser with an oscillation wavelength of 0.78 μm, an optical output of 30 to 50 mW in a fundamental transverse mode, and a maximum optical output IW was obtained. In addition, the structure of Example 2 with transparent end faces has an oscillation wavelength of 0.76 to 0.80 μm and an optical output of 10
A semiconductor laser with a fundamental transverse mode down to 0 mW and a maximum optical output of 2 W was obtained.

The present invention is not limited to the wavelength of around 0.78 μm as shown in the example, but the C
Similar results were obtained over the entire range in which W oscillation was possible. Also,
The present invention is applicable to laser materials other than GaAtAS, such as I
The same can be applied to nGa As P and InGaP systems.

〔Effect of the invention〕

According to the present invention, the refractive index of the n-type cladding layer and the n-type cladding layer are made asymmetric, and the thickness of the cladding layer adjacent to the light guide layer is less than 1.0 μm, thereby achieving transverse mode stabilization and high output. It has the effect of achieving both As a result of device fabrication, it has become possible to obtain devices with a fundamental transverse mode up to an oscillation wavelength of 0.78 μm and an optical output of 50 mWCW at a high yield. Also,
If the active layer is made into a quantum well type, the optical output i oomwcwt
The fundamental transverse mode is maintained, and the threshold current value is 30 nlW.
It was below. By making the end face transparent, the maximum light output was IW when the active layer was a single layer with a thickness of about 0.06 μm, and was 2W when the active layer was a double-well type. From the above, it has become clear that this ξ light is quite effective in achieving both transverse mode stabilization and high output.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional BH type laser with a light guide layer.
Figure 2 is a cross-sectional view of the 15BH type laser, Figures 3 and 4.
The figure shows the calculation results of the light intensity distribution of TEo and TEs modes.
Fig. 5 is a cross-sectional view of a 15BH type laser made of a light-absorbing semiconductor cap scrap material according to the present invention, and Fig. 6 is a sectional view of an 8B type laser according to the present invention.
) A cross-sectional view of a T-type laser, FIG. 7 is a method for manufacturing an SBH-type laser according to the present invention, and a cross-sectional view thereof, FIG. 8 is a cross-sectional view of a device having a quantum well type active layer, and FIG. 9 is a cross-sectional view of a transparent end face. FIG. 3 is a cross-sectional view of the device in the laser optical axis direction in the case of the above. Figure 1 1...n-(1aAs substrate, 2-n-GaA
tA3 cladding layer, 3... n-GaAtAS optical guide layer, 4... undoped GaAtA3 active layer, 5.
I)-GaAtAS cladding layer, 6...p-aaAt
As buried layer, 7... n-GaA3 substrate buried layer, 8... Zn diffusion layer, 9... n-electrode, 10...
p-electrode' Fig. 2 1...-n-QAAs substrate, 2,...n
-G ao, so At64 (I A S cladding layer, 3... undoped Ga o, os Ato, as
AS active layer, 4...I) -Gan, ysA-
10, As light guide layer, 5... pG ao, ss
Ato, sy As cladding layer, 6''' GaO,
4OA 16.66 A S buried layer, 7...n
oat-, AtyA8 buried layer, 8-8jO* insulating film, 9... Zn diffusion layer, 10... n- electrode, 11...
・P-electrode Figure 5 1-n-GaA3 substrate, 2-n-GaAtA
S cladding layer, 3... undoped GaAtA3 active layer, 4. P-QaAtA8 optical guide layer, 5. I)-
GaAtAS cladding layer, 6...I)-GaAS cap layer, 7...p-GaAtAs buried layer, 8-n
-Ga AtAS buried layer s 9-sro*insulating film, 1O-Zn diffusion layer, 11...n-electrode, 12...
p-electrode Fig. 6, Fig. 7, Fig. 9 1-n-QaAs substrate, 2...n-Ga@, 7OAto, so As
Cladding layer, 3-nGao, 74Alo,
241 AS optical guide layer, 4... undoped Gao
, ss Ato, +n As active layer, 5 ・9-Gao
, 5sAt0. uAs cladding layer, 6-p-Gao,s
o Ato, iAsAs character, 'y・-p Gao
-5sAto, n5As buried layer, 8"'"G
ao-ss A/! o, 46 A S embedded layer, 9
...Zn diffusion layer, 10...n-electrode, 11...p
- Electrodes. Figure 4 ↑ Figure 1 = il? Distance in the vertical direction χ [[inertia]] 5th
Mouth 0 Figure B η R Figure δ Figure YJ 9 Old

Claims (1)

[Claims] 1. A semiconductor laser device that has an optical guide layer adjacent to an active layer, and in which the sides of the mesa stripe are embedded with at least one layer that has a larger forbidden band width and a lower refractive index than the active layer. In the semiconductor laser, the thickness of the cladding layer adjacent to the optical guide layer is less than 1.0 μm, and the semiconductor laser has a semiconductor layer adjacent to the cladding layer and having a narrower band gap than the active layer. Device. 2. In the semiconductor laser device according to claim 1, the refractive index difference between the n-type cladding layer and the p-type cladding layer is 0.
A semiconductor laser device characterized in that the difference is in the range of 0.01 to 0.20. 3. A semiconductor laser device according to claims 1 and 2, characterized in that the width of the optical guide layer is 1 μm or more larger than the width of the active layer. 4. A semiconductor laser device according to any one of claims 1 to 3, wherein the light guide layer has an n-type conductivity. 5. In the semiconductor laser device according to claim 3, the conductivity type of the light guide layer is n type, the width of the light guide layer on the active layer side is wider than the width of the cap layer on the substrate side, and A semiconductor laser device characterized in that a width of a guide layer on a substrate side is wider than a width on an active layer side. 6. A semiconductor laser device according to any one of claims 1 to 5, characterized in that the buried layer reaches the substrate. 7. In the semiconductor laser device according to any one of claims 1 to 6, the active layer has a thickness of one or more layers.
A semiconductor laser device characterized by having a quantum well layer of 300 to 300 people. 8. In the semiconductor laser device according to any one of claims 1 to 7, the optical guide layer exists up to the reflective end face of the laser resonator, and the active layer end face is located inside the reflective end face. A semiconductor laser device characterized by: