JPS60226191A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser element which has an advantage of having no low Ith, height no and astigmatism, by a method wherein effective refractive index difference DELTAn and loss difference DELTAalpha at the inside and outside of a base plate groove are controlled independently. CONSTITUTION:At the outside of V type groove 19, the light strength distribution becomes non-contrastive vertically as if pushed in the direction of an n-clad layer 15 by the presence of a layer 20 (low refraction ratio) having larger AlAs molar ratio than a p-clad layer 13, and the effective refraction ratio is lowered. As a result, a refraction ratio guide wave route is formed on a groove 19. The light absorbing condition to an electric current inhibition layer 12 at the outside of the groove 19 can be changed by the width of the layer 20 and AlAs molar ratio (z). Accordingly, DELTAn and DELTAalpha can be controlled independently, and it will be possible to make large DELTAn and small DELTAalpha.

Description

Detailed Description of the Invention Technical Field The present invention relates to a semiconductor laser device with a controlled transverse mode of oscillation, and in particular to the device structure and manufacturing of a semiconductor laser in which an intermediate layer with a controlled refractive index is interposed on a substrate. It is about the method.

<Prior art> As an example of an index-guided semiconductor laser, an internal stripe-type vSIS (V-channel
ed 3ubstrate Inner 5tripe
) laser is known. Details of this semiconductor laser can be found in IEICE technical report ED81-42.31 (1981).
(July, 2013). An example of a VSIS semiconductor laser device is shown in cross-section in FIG.

Also, the refractive index (n) distribution and loss (ri) in the direction parallel to the active layer.
The distribution is also shown at the same time. 1 is a p-GaAs substrate, 2 is an n-GaAs current blocking layer, 3 is a p-GaAnA
s cladding layer, 4 is GaAnAs active layer, 5 is n
-GaAs substrate cladding layer, 6 is an n-GaAs cap layer, 7 is an n-side electrode, and 8 is a p-side electrode.

Note that the cross-sectional view of FIG. 1 shows the light intensity distribution in the direction perpendicular to the active layer. The light generated in the active layer is absorbed by the n-GaAs current blocking layer 2, producing an effective refractive index difference Δn and a loss difference Δα between the inside and outside of the 7-shaped groove of the substrate 1. Δn contributes to light confinement, and Δα suppresses the generation of higher-order modes. Δn and Δα can be controlled by changing the thickness of the active layer 4 and the thickness of the p-cladding layer 3 outside the groove.

However, when trying to thicken Δn, at the same time Δα
They are also thick (and cannot be controlled independently.

Therefore, in the conventional VSIS semiconductor laser, Δα is 500
1' or less, the threshold current Ith increases, and the differential quantum efficiency η. In this case, the lens was forced to suffer from a decrease in image quality and the presence of astigmatism.

<Object of the Invention> The present invention achieves low 1th,
High η. It is an object of the present invention to provide a semiconductor laser device having the advantages of having no astigmatism and no astigmatism.

<Example> An example of the semiconductor laser device of the present invention will be described with reference to FIG. The laser element structure of this example is G
This is a VSIS laser with a double heterojunction structure based on an aAs-GaAs substrate. 11 is a p GaAs substrate, 1
2 is an n' GaAs current blocking layer.

13 is p'-Ga,, A[, As cladding layer, 14 is pG a 1. , AI! xAs active layer, 15 an n-Ga11A%As cladding layer, and 16 an nGaAs cap layer.

17 is an n-side electrode, 18 is a p-side electrode, and 19 is a ■-shaped groove having a width W. Also, 20 is p or n-Ga, □Aj? 2A
This is the middle layer of s. Aj of each layer? A s molar ratio is 0≦x
Set <y<z<1. On the outside of the V-shaped groove 19, due to the presence of the layer 20 having a higher A4As molar ratio (lower refractive index) than the p-cladding layer 13, the light intensity distribution becomes vertically asymmetrical as if pushed in the direction of the n-cladding layer 15. , the effective refractive index decreases. As a result, a refractive index waveguide is formed on the groove 19. In addition, the current blocking layer 1 outside the groove 19
The state of light absorption into the layer 20 can be changed by the thickness of the layer 20 and the AβAs molar ratio zlc. Therefore Δn and Δ
α can be controlled independently, making it possible to create a size Δn and a small Δα. It is sufficient that the magnitude of Δα is about 100 to 3001, which is necessary to suppress the generation of higher-order modes.

Generally, when liquid phase epitaxial (LPE) growth is used, G a A 13 A s once exposed to air
It is difficult to continuously grow an epitaxial layer thereon due to oxidation formed on the surface. However, this is the case when the underlying GaAA'As has a large area, and G
aAJ? When the As layer is grown by liquid phase epitaxial growth, the above-mentioned problem does not arise (it can be grown continuously).

Therefore, the width of the layer 20 inserted between the current blocking layer I2 and the p-cladding layer 13 is set to 10 μm or less to enable continuous growth.

Furthermore, the layer 20 also serves as a meltback prevention layer to prevent the grooves 19 from deforming due to meltback.

Generally, if the groove shoulders are made of GaAs, meltback is likely to occur (and if the shoulders are made of GaAnAs, meltback is difficult to occur).

Next, the method for manufacturing the semiconductor laser device shown in FIG.
This will be explained using the process diagram shown in the figure. Figure 3 (Al
As shown in tlcP-GaAs substrate (Zn-doped IO-1 row-1 to 1.-+, stop layer (Te doped, 3 1018ff”) 20 are superimposed and each is 0.5
Liquid phase epitaxial growth is performed to a thickness of 0.3 μm.

Next, as shown in FIG. 3(B), the intermediate layer 20 is processed by photolithography technology and chemical etching.
It is left in a stripe shape with a width W=8 μm. Next, the third
As shown in FIG. By forming the V-shaped groove 19, a current path is opened in this part where the current blocking layer 12 is removed, and a stripe structure is obtained.A stripe structure is obtained by forming the V-shaped groove 19 again by liquid phase epitaxial growth on this substrate 11, as shown in FIG. pcaO,7A4o,3As cladding layer 13
゜p Ga□, g5A%o5AS active layer 14 + n
Gao, 7 A go3As cladding layer 15, n
- GaAs cap layer 16 upper layer 6 each 0.2 μm, 0
．． Thicknesses of 0.8 μm, 1 μm, and 2 μm form the laser oscillation operating portion of the thickness of 0.08 μm, 1 μm, and 2 μm.

In this case, the molar ratio of Ajl'As in each layer is X20.05
, , Y = 0.3, z = 0.4.

n-Gao6 A6o4 As exposed before growth
Since the area of the layer 20 is small, the G coated on it during growth is
There is no problem in wetting the a solution, and a good epitaxial growth layer without defects such as pinholes can be obtained.

After ramping the back surface of the substrate to a thickness of about 100 μm, Au-Ge-N i was applied as an n-side electrode 17 on the surface of the n-GaAs cap layer 16, and a p-side electrode was applied on the back surface of the p-GaAs substrate 11. A as electrode 18
Deposit u-Zn and heat to 450°C for rationalization. Thereafter, the device is completed by opening it so that the resonator length becomes 250 μm. This element is mounted on a copper heat sink with indium metal interposed therebetween so that the n-side electrode 17 is in contact with the heat sink to form a semiconductor laser.

Zn of the semiconductor laser thus obtained.

According to the calculation, Δα is Δn=6XIo−3゜Δα, respectively.
-150ff'. In addition, this semiconductor laser has a threshold current I th = 25 mA + a wavelength of 820 nm.
The external differential quantum efficiency is ηゎ-3 on one side of the resonator.
It exhibits a high value of 0%. In addition, the beam oscillated in a stable fundamental transverse mode up to an optical output of 30 mW, and the beam waist coincided with the end face.

FIG. 4 is a sectional view of a high optical output semiconductor laser showing another embodiment of the present invention. The difference from the previous embodiment is that the substrate 21
A trapezoidal mesa 31 having a height H of 3 μm and a width of 10 μm is formed on the top by etching in advance.

On this substrate 21, n-GaAs is deposited by MO-CVD method.
A current blocking layer 22゜p-G"l-z Aj?□As intermediate layer 30 is laminated. The feature of the MO-CVD method is that the Ebitaki soyal layer grows to a uniform thickness according to the shape of the mesa 31 on the substrate 21. The subsequent steps are similar to those in the previous embodiment, but this embodiment has an advantage in that the thickness of the active layer 24 in the flat region can be easily made thin.

In order to increase the optical output of a semiconductor laser, the active layer thickness should be reduced to 0.
It is more effective to reduce the thickness to about 0.05 μm.

However, in the past, it has been difficult to grow such thin layers uniformly. Therefore, in this embodiment, many EAs atoms on both sides of the mesa 31 on the substrate 21 are attracted during active layer growth by liquid phase epitaxial (LPE) method.
The thickness of the flat active layer on the mesa 31 can be easily reduced to about 0.05 μm.

The semiconductor laser of this example oscillated in a stable fundamental transverse mode up to 50 mW. Further, other characteristics were the same as those of the previous example.

Note that if the conductivity type of the intermediate layer 20.80 is p-type, Ith will increase by several mA due to current waves, or the carrier distribution in the active layer will become uniform, resulting in poor coherence of laser light. It has the advantage of being good.

The semiconductor laser of the present invention has the above-mentioned GaAs-G
aAj? Not limited to As-based, but also InP-InGaAsP
It can be applied to other heterojunction lasers such as In this case, it is necessary to select the intermediate layer so that its refractive index is smaller than that of the cladding layer.

<Effects of the Invention> As described above, the semiconductor laser of the present invention has a built-in refractive index distribution Δn and a loss distribution Δα of -1-1++, respectively.
,,y41#,-L l/,VQ Todoroki+y a+ 佽-Ae candy 2 days n<r++41'1 layer A#As
By changing the molar ratio 2 and its thickness, it is possible to achieve large Zn and small Δα at the same time.
, high η. , a semiconductor laser with astigmatism and a stable fundamental transverse mode is fabricated.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a conventional VSIS laser. FIG. 2 is a sectional view of a semiconductor laser device showing one embodiment of the present invention. FIG. 3R) (13+fc) is a process diagram showing the manufacturing process of the semiconductor laser device shown in FIG. FIG. 4 is a sectional view of a semiconductor laser also showing another embodiment of the present invention. 1,11,21・-P GaAs substrate, 2,12゜22-n-GaAs current blocking layer, 3,13.23-P
-Ga AlAs cladding layer, 4, 14.24...-G
a AI As active layer, 5,1.5.25・=n-Ga
AA'As cladding layer, 6,16.26-n-G・a
A,'s key layer, 7, 17.27-n side electrode, 8.18.28...P side electrode, 9, 19.29...
・7-shaped groove, 20.30-n or p-Ga A6 As
Middle class, 31...Mesa.

Claims (1)

[Claims] 1. In a semiconductor laser device in which a multilayer crystal layer for laser oscillation is laminated using a stripe groove formed on a substrate as a current path, there is a refraction layer adjacent to the substrate side of the multilayer crystal layer and refracted at positions on both sides of the stripe groove. 1. A semiconductor laser device characterized in that an intermediate layer having a low index is inserted to impart an effective refractive index distribution to an active layer within the multilayer crystal layer.