JPH047113B2 - - Google Patents

Description

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

<Prior art> One of the factors that limits 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. At this time, the end face destruction output (hereinafter referred to as
Pmax) is
It was ^about 106W/cm2. For example, the WS laser (Appl.Phys. .Lett.15May 1979
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, 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 laser oscillation region end faces 5, 5' in the direction parallel to the junction, and at the cavity end faces 3, 5' in the direction perpendicular to the junction.
3'. This astigmatism is inconvenient when optical coupling is performed using a lens or the like.

<Object 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 device. That is, an optical waveguide is also formed in the window region, and a tapered coupling region is provided between the excitation region (laser oscillation operating region) inside the cavity and the window region to couple the excitation region and the window region. , to cause laser oscillation. With such a configuration, the laser oscillation mode can be controlled in the window region, and the beam waist can be made to coincide with the end face.
Furthermore, it is also possible to stabilize the mode of a semiconductor laser which is easily disturbed at high output. The present invention establishes such a semiconductor laser device.

<Example> FIG. 2 is a diagram showing how light propagates within a semiconductor laser device according to an example 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 arranged at both ends of a laser oscillation operating region 21 having a waveguide width W _g1 and a length L _e , Tapered joints 23, 23' having lengths L _T and L _T ' are connected between both window areas 22, 22' and the operating area 21. The length of the laser oscillation operating region 21 is limited by the laser oscillation region end faces 25, 25'. The propagation wavefront 26 of the laser beam is as shown in the figure, and the laser beam is emitted from the resonator end faces 24, 24'. 3A and 3B are cross-sectional views taken along line X-X and line Y-Y in FIG. 2. 3A is a sectional view of the laser oscillation operating region 21, and FIG. 3B is a sectional view of the window regions 22, 22'.

An n-GaAs current blocking layer 32 for blocking current is deposited on the p-GaAs substrate 31;
Striped grooves are formed in the current blocking layer 32 and the GaAs substrate 31. On top of this p-
GaAlAs cladding layer 33, GaAs or GaAlAs active layer 34, n-GaAlAs cladding layer 35, n-
GaAs cap layers 36 are sequentially laminated.

The structure shown in Figure 3A is the so-called active layer curved VSIS.
The laser shown in FIG. 3B has the same structure as the active layer flat type VSIS laser. VSIS (V-
Regarding the channeled Substrate Inner Stripe) laser, see the Institute of Electrical Communication Engineers Technical Report (ED-81-42).
(1981, p. 31), etc., but the V
This is an internal stripe type laser with a light and carrier confinement structure in which a current path is formed by processing grooves. In other words, the current for laser oscillation is n-GaAs
are blocked by layers 32 and have widths W _c1 and W _c2 , respectively.
Flows only through the channel. These channel widths are formed so that W _c1 >W _c2 , and under the same growth conditions, the active layer can be formed curved in the former case, and flat in the latter case. When the active layer is curved, a refractive index optical waveguide is formed, and its width
W _g1 is narrower than the channel width W _c . Furthermore, if the active layer 34 is flat, n-
An optical waveguide is formed using the principle that the effective refractive index decreases due to light absorption into the GaAs layer 32, and its width
W _g2 is approximately equal to the channel width W _c2 .

The important event that led to the creation of the present invention is that when a curved active layer VSIS laser and a flat active layer VSIS laser are manufactured separately under the same growth conditions,
The former always oscillates at a longer wavelength by 100~200〓, that is, the bandgap is narrower by 21~42 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 optical waveguides having these two types of active layers are formed at the same time and effectively coupled, laser oscillation will occur in the curved portion, and the laser light will simply pass through the flat portion. Therefore, by arranging the active layer so that the flat portions are located near both end faces, the oscillation threshold current I _th can be reduced and the transverse mode can also be stabilized. Furthermore, it is possible to fabricate a semiconductor laser with less end face deterioration or a large end face breakdown durability output Pmax. In other words, the two types mentioned above
It is possible to use only the advantages of the VSIS laser and compensate for its disadvantages, and moreover, it is possible to easily manufacture a window type laser.

An example of the manufacturing method of the present invention will be described below.

4A, B, C, and D are manufacturing process diagrams illustrating one embodiment of the manufacturing method.

First, an n-type GaAs layer (Te-doped, carrier concentration 6×10 ¹⁸ cm ^-3 ) 42 of approximately 0.6 μm is deposited on a p-type GaAs substrate (Zn doped, carrier concentration 1×10 ¹⁹ cm ^-3 ) 41.
Liquid phase epitaxial growth to a thickness of . Thereafter, a striped pattern of varying width as shown in FIG. 4A is formed on the surface of the n-type GaAs layer 42 by conventional photolithography. The resist used was AZ1350 manufactured by Shipprey, and the dimensions of each part were L ₁ = 150 μm, L ₂ = 100 μm, L ₃ = 20 μm,
A window is formed such that W _c1 =6 μm and W _c2 =3 μm. Through this window, use a sulfuric acid-based etching solution.
Etch the GaAs layer 42. Furthermore, Z ₁ −Z ₁ , Z ₂
-Z cross-sectional shapes in _{the two} directions are shown in Figures 4B and C, 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. The thickness of the wafer is reduced to approximately 100μ by wrapping the backside of the substrate.
After m, the surface of the n-GaAs cap layer 36 is
Au-Ge-Ni and p-GaAs substrate 31 on the back side.
Au-Zn is deposited and heated to 450°C to form an alloy to form an electrode layer. Next, p-GaAs substrate 3
After Al is deposited on the back surface of 1, a pattern matching the pitch of the internal channels is formed as shown in FIG. 4D. 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 type laser oscillates at 1 _th = 30mA,
The wavelength at that time was 7800〓. Further, the end face breaking power Pmax was approximately 100 mW. Moreover, 100mW
It oscillated in a stable transverse fundamental mode until

Next, when the active layer was cleaved at the curved laser oscillation region to form a resonator, it oscillated in a higher-order transverse mode and the end face was destroyed at approximately 10 mW. Therefore, the window laser of the present invention improves Pmax by about 10 times. Furthermore, when the end face was coated with Al ₂ O ₃ , Pmax improved to about 200 mW. Furthermore, when a window type laser with an oscillation wavelength of 8300㎜ was manufactured, Pmax = 200 mW without end face coating, and Pmax = 400 mW with end face coating.

Here, if the coupling regions 23 and 23' are not provided, coupling will not be performed effectively, resulting in a decrease in differential efficiency (about 1/2 that of a normal VSIS laser), and coupling efficiency will vary depending on the ambient temperature. There were inconveniences such as the oscillation mode changing. When the coupling area was increased to 20 μm or more, the differential efficiency was improved to 90% of normal VSIS, and stable oscillation was obtained even at ambient temperatures.

When window lasers with oscillation wavelengths of 7,800 Å and 8,300 Å were operated continuously at an output of 30 mW and 50°C, no deterioration was observed 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. Furthermore, the present invention is applicable not only to semiconductor lasers but also to mode converters for optical integrated circuits.

<Effects of the Invention> As detailed above, according to the present invention, the excitation region that performs the laser oscillation operation and the window regions provided at both ends of the excitation region are connected by the tapered coupling region, and the width of the waveguide is reduced. Since the coupling between the narrow excitation region and the wide window region of the waveguide is performed continuously in the coupling region where the waveguide width changes in a tapered manner, the oscillation mode can be stabilized even during high-power operation.
Furthermore, it becomes possible to improve the differential efficiency and to stabilize it against ambient temperature, and a highly reliable semiconductor laser device with good device characteristics can be obtained.

[Brief explanation of drawings]

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. 4A, B, C, and D are manufacturing process diagrams illustrating an embodiment of the manufacturing method of the present invention. 21... Laser oscillation operating area, 22, 22'...
... Window area, 23, 23'... Connection area, 25, 2
5'...Laser oscillation region end face, 31...p-
GaAs substrate, 32... n-GaAs current blocking layer, 33... p-clad layer, 34... active layer, 35... n-clad layer, 36... n-cap layer.

Claims (1)

[Claims] 1 An excitation region having a curved active layer and a window region having a flat active layer at both ends of the resonator are provided in response to changes in the stripe width of the current confinement groove formed on the substrate, and a gap between the excitation region and the window region is provided. A semiconductor laser device characterized in that the two waveguides are connected by a coupling region whose waveguide width changes in a tapered manner determined by the width of both waveguides.