JPH0474876B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new structure of a semiconductor laser device having a window region that absorbs little laser light.

One of the factors that controls the lifespan of semiconductor lasers is
It is well known that the resonator end face, which serves as the light exit face, deteriorates. Further, when the semiconductor laser device is operated at high output, this cavity end face may be destroyed. The end face breaking output at this time (hereinafter referred to as
Pmax) is
It was about 10 ⁶ W/cm ² . For example, the WS laser (Appl-Phys. Lett.15 May1979
P.637) has been proposed. Alternatively, a structure in which the vicinity of the end face is filled with a material having a wider band gap than the active layer is also known.

However, in these window-type semiconductor lasers, no optical waveguide is formed in the window region in a direction parallel to the junction. Therefore, as the laser light spreads and propagates in the window region, the amount of light that is reflected by the resonator reflection surface and returns to the laser oscillation region is reduced, resulting in a decrease in oscillation efficiency and a high oscillation threshold current. It has some drawbacks. FIG. 1 shows how light propagates in a conventional window-type semiconductor laser device when viewed from the top of the laser device. That is, window regions 2 and 2' are formed in the direction of both resonant ends of the striped laser oscillation operating region 1, and the resonator end faces 3 and
Laser beams 4, 4' are output from 3'. still,
The laser oscillation region end faces 5, 5' are the resonator end faces 3,
3', and from this position the laser light travels as shown by a propagation wavefront 6.

The focal point (beam waist) of the laser beam is located at the end faces 5, 5' of the laser oscillation region in the direction parallel to the bonding.
, and in the direction perpendicular to the junction, the resonator end face 3,
3'. This astigmatism is inconvenient when optical coupling is performed using a lens or the like.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor laser device having a novel structure that overcomes the drawbacks of the conventional window type semiconductor laser.

That is, by forming an optical waveguide also in the window region, the beam waist exists on the resonator end face both horizontally and vertically to the junction. Furthermore, it is possible for the window region of the semiconductor laser to suppress the higher-order transverse modes generated in the laser oscillation region and guide only the fundamental transverse mode, which is an extraordinary feature not found in conventional window-type semiconductor lasers. This is an effect that has improved significantly.

In addition, in order to prevent current from flowing near the resonator, conventional methods have been used such as forming an insulating film on the surface, but the current spreads large in the cladding layer and cap layer above the active layer, making the resonator inefficient. There was no proper current blocking. However, according to the present invention, the current blocking layer can effectively block current flow in the vicinity of the resonator. Furthermore, the formation method does not require the conventional zinc diffusion process, and is very simple and practical.

Hereinafter, the present invention will be explained in detail according to embodiments with reference to the drawings.

FIG. 2 is a diagram showing how light propagates within a semiconductor laser device according to an embodiment of the present invention, viewed from the top of the laser device.

Window regions 22 and 22' having a waveguide width W _g2 and respective lengths L _w and L _w ' are disposed at both ends of a laser oscillation operating region 21 having a waveguide width W _g1 and a length L _e , Laser beams 24, 24' are emitted from the resonator end faces 23, 23'. The length of the laser oscillation operating region 21 is limited by the laser oscillation region end faces 25, 25'. Laser light has its propagation wavefront 2
6 as shown in the figure.

Figure 3 A and B are X-X and Y in Figure 2.
-Y sectional view. That is, FIG. 3A is a cross-sectional view of the laser oscillation operating region 21, and FIG. 3B is a cross-sectional view of the window region 2.
2, 22' is a sectional view.

An n-GaAs current blocking layer 32 for blocking current is deposited on the p-GaAs substrate 31, and this current blocking layer 32 covers the window regions 22,
22' is formed to be thicker than the laser oscillation region 21. In addition, the current blocking layer 3
2 and the GaAs substrate 31 are provided with striped grooves. On top of this is a p-GaAlAs cladding layer 3.
3. GaAs or GaAlAs active layer 34, n-
A GaAlAs cladding layer 35 and an n-GaAs cap layer 36 are sequentially laminated.

The structure shown in Figure 3A is the so-called active layer curved VSIS.
The laser shown in FIG. 3B is also a VSIS laser with a flat active layer. VSIS (V-channeled Substrate)
Regarding Inner Stripe) lasers, see the Technical Report of the Institute of Electrical Communication Engineers (ED81-42, 1981, P.31) and Appl.
As described in detail in Phys. Lett. (1 March 1982, P. 372), it is an internal stripe type laser that has a light and carrier confinement structure in which current paths are formed by cutting grooves in the substrate. That is, the current for laser oscillation is blocked by the n-GaAs layer 32 and flows only in the channel portions having widths W _c1 and W _c2 , respectively. These channel widths are formed so that W _c1 >W _c2 , and under the same growth conditions, the active layer can be curved in the former case, and the active layer can be flattened in the latter case. When the active layer is curved, a refractive index optical waveguide is formed, the width W _g1 of which is narrower than the channel width W _c . In addition, when the active layer 34 is flat, an optical waveguide is formed using the principle that the effective refractive index decreases due to light absorption into the n-GaAs layer 32 at both ends of the channel, and its width W _g2 is approximately equal to the channel width W _c2 . equal.

The important event that led to the creation of the present invention is that when a curved active layer VVSIS laser and a flat active layer VSIS laser are individually fabricated under the same growth conditions, the former always has a longer wavelength by 100 to 200 Å. This means that the band gap narrows by 21 to 42 meV. Furthermore, when the active layer is curved, the oscillation threshold current becomes smaller, but the transverse mode tends to become unstable, and when the active layer is made flat, the oscillation threshold current increases slightly, but the transverse mode becomes very stable. be. Therefore, if an optical waveguide having these two types of active layers is formed at the same time, laser oscillation will occur in the curved portion, and the laser light will simply pass through the flat portion. Therefore,
By arranging the flat portions of the active layer near both end faces, the oscillation threshold current I _th can be reduced and the transverse mode can also be stabilized. Moreover, the output Pmax with little end face deterioration or end face breakdown durability
It is possible to fabricate a semiconductor laser with a large size.
In other words, it is possible to utilize only the advantages of the two types of VSIS lasers mentioned above and compensate for their disadvantages.
Moreover, a window-shaped laser can be easily manufactured. However, if the same current flows through the window regions 22, 22' as in the laser oscillation region 25, the laser oscillation conditions will be satisfied in the window regions 22, 22' with a laser output of about 20 mW, and the transverse mode will be easily disturbed. This results in some disadvantages. In the window type laser of the present invention, since the current blocking layer 32 is present even at the center of the channel in the window regions 22, 22', laser oscillation does not occur, and the active layer only functions as a window for laser light. Therefore, the transverse mode is not disturbed and is stable up to about 100 mW.

An example of the manufacturing method of the present invention will be described below. 4A, B, C, D, and E are manufacturing process diagrams illustrating one embodiment of the manufacturing method.

First, a P-type GaAs substrate (Zn doped, 1×10 ¹⁹ cm
^-3 ) On 41, the width W _c0 = as shown in Figure 4A
Rectangular groove 40 of 10 μm, length L ₂ = 100 μm, depth 1 μm
are formed by photolithography at intervals of L ₁ =150 μm. The resist used was from Shitsuplay.
The GaAs substrate 41 is etched using a sulfuric acid-based etching solution through this window.

Next, an n-type GaAs layer (Te doped, 6×10 ¹⁸ cm ⁻³ ) 42 is grown on the substrate 41 to a thickness of about 0.8 μm by liquid phase epitaxial growth. At this time, the rectangular groove 40
is completely buried, and the n-type GaAs layer 42 has a thickness of 1.8 μm.

Thereafter, a striped pattern of varying width as shown in FIG. 4B is again formed on the surface of the n-type GaAs layer by photolithography. Dimensions of each part are L ₁ = 150μm, L ₂ = 100μm, W _c1 = 6μm, W _c2 =
It is 3μm.

Through this window, GaAs was etched using a sulfuric acid-based etching solution.
Etch layer 42. The cross-sectional shapes in the Z ₁ -Z ₁ and Z ₂ -Z ₂ directions are shown in FIGS. 4C and D, respectively.

Then, using liquid phase epitaxial technology again,
As shown in FIG. 3, p-Ga _0.5 Al _0.5 As cladding layer 33, p-Ga _0.85 Al _0.15 As active layer 34, n-Ga _0.5
Al _0.5 As clad layer 34, n-GaAs cap layer 3
6 is 0.15μm, 0.1μm, 1.0μm at the flat part, respectively.
It was grown to 2 μm. However, the active layer thickness at the center of the curved part of the active layer was 0.2 μm. After the back surface of the substrate is lapped to make the wafer thickness approximately 100 μm, the surface of the n-GaAs cap layer 36 is coated with Au-
Ge-Ni and Au-Ni on the back side of the p-GaAs substrate 31.
Zn is deposited and heated to 450°C to form an electrode layer. Next, Al is deposited on the back surface of the p-GaAs substrate 31, and a pattern matching the pitch of the internal channels is formed as shown in FIG. 4E. It is then cleaved at the center of the window region with length L ₁ to form a resonator. The window regions will therefore have a length of 50 μm at each end of the element.
This window laser oscillated at I _th =30 mA, and the wavelength at that time was 7800 Å. Also, end face destruction output
Pmax was approximately 100mW. Moreover, it oscillated in a stable transverse fundamental mode up to 100mW. Next, the active layer was cleaved in the curved laser oscillation region to form a resonator, which oscillated in a higher-order transverse mode and broke at the end face at approximately 10 mW. Therefore, with the window laser of the present invention,
This means that Pmax has improved approximately 10 times.

Furthermore, when the end face was coated with Al ₂ O ₃ , Pmax improved to approximately 200 mW.

In addition, when we fabricated a window laser with an oscillation wavelength of 8300 Å, Pmax = 200 mW without end face coating, and Pmax = 400 mW with end face coating.

Window lasers with oscillation wavelengths of 7,800 Å and 8,300 Å were operated continuously at 50°C with an output of 30 mW, with no deterioration after 2,500 hours.

The semiconductor laser of the present invention is as described in the above embodiment.
It is clear that the present invention is applicable not only to GaAlAs-based lasers but also to InP-InGaAsP-based and all other heterojunction lasers.

[Brief explanation of the drawing]

FIG. 1 is a plan view illustrating the propagation of light in a conventional window laser. FIG. 2 is a plan view illustrating light propagation of a window laser according to an embodiment of the present invention. Figures 3A and B are X-X in Figure 2, respectively.
It is a YY cross-sectional view. Figure 4 A, B, C, D, E
FIG. 2 is a manufacturing process diagram illustrating an embodiment of the manufacturing method of the present invention. 21... Laser oscillation operating area, 22, 22'... Window area, 23, 23'... Resonator end face, 25, 25'...
Laser oscillation region end face, 31... p-GaAs substrate, 3
2...n-GaAs current blocking layer, 33...p-
Clad layer, 34...active layer, 35...n-clad layer, 36...n-cap layer.

Claims (1)

[Scope of Claims] 1. A substrate, a current blocking layer formed on the substrate, a striped groove formed to reach the substrate from the current blocking layer, and a striped groove corresponding to the striped groove. a laser oscillation region provided with a curved active layer having a width narrower than the width of the striped groove; and a region located near the cavity surface on both sides of the laser oscillation region, the substrate being covered with the current blocking layer; Further, a current blocking layer covering the substrate is provided with a striped groove having a width narrower than the striped groove width of the laser oscillation region, and a flat active layer corresponding to the striped groove, so that oscillation is caused. A semiconductor laser device comprising: a laser light window region in which the laser light is absorbed by the current blocking layer.