JP2889628B2 - Broad area laser - Google Patents

Description

The present invention relates to a broad area laser used for optical information processing, laser processing, and the like.

(B) Conventional technology In recent years, as semiconductor lasers have become widespread and their application fields have expanded, high-power semiconductor lasers used for optical information processing, laser processing, and the like have been required.

At present, high-power semiconductor lasers include broad-area lasers and semiconductor laser arrays. Among them, the broad area laser is described, for example, in the magazine “Electronic Materials”, June 1987, 103
As shown on pages 106 to 106, the current path width, which is usually limited to a width of several μm by the current constriction layer, is increased to several tens to several hundred μm, thereby distributing the laser light over a wide range. In addition, the end face of the active layer is prevented from being destroyed due to light concentration, and high output is enabled.

However, in such a broad-area laser, since the laser light is widely distributed in a direction parallel to the bonding surface in the laser resonator, a higher-order mode is easily generated in the transverse mode of the laser light, and the laser is multi-moded. Filament oscillation occurs in which the light distribution of the laser light suddenly rises. Therefore, there is a problem that the laser light cannot be focused on a small spot.

Therefore, as a method of controlling the transverse mode in such a broad area laser, as disclosed in, for example, RTM-88-25, a report of the Laser Society of Japan (1988), the current path central portion of the laser resonator end face is used. There is a method of providing a high reflection portion.

However, in such a method, since a reflective film must be formed partially on the end face of the laser resonator of a small chip, there is a problem that manufacturing is difficult and the process becomes complicated.

(C) Problems to be Solved by the Invention Accordingly, the present invention provides a broad area laser that is easy to manufacture and can control the transverse mode.

(D) Means for Solving the Problems The present invention is a broad area laser in which the width of a stripe-shaped current path extending along a laser resonator permits oscillation in a higher-order transverse mode. To solve,
On the current path, a first electrode portion that contacts a semiconductor layer in the current path at an end of the current path, and a second electrode portion that contacts the semiconductor layer at a center portion of the current path, A contact resistance between the first electrode portion and the semiconductor layer in the current path is higher than a contact resistance between the second electrode portion and the semiconductor layer.

(E) Function According to the present invention, the first electrode portion contacts the semiconductor layer in the current path at the end of the current path on the current path, and contacts the semiconductor layer at the center of the current path. A second electrode portion, wherein a contact resistance between the first electrode portion and the semiconductor layer is made higher than a contact resistance between the second electrode portion and the semiconductor layer, so that a width of the second electrode portion in the current path is reduced. A current intensity distribution that is high at the center in the direction and low at the ends is formed.

(F) Embodiment First, the principle of the present invention will be described.

In general, multimode oscillation in a broad area laser having a wide current path is caused by giving a gain to a higher-order mode that can exist in the current path. Therefore,
By forming a high gain distribution for the fundamental mode and a low gain distribution for the higher-order mode in such a current path, it is possible to selectively oscillate only the fundamental mode.

Here, the gain g is g, where β is the gain constant, J is the injection current density, and J ₀ is the injection current density when the gain becomes 0.
= Β (J−J ₀ ). That is, the gain distribution can be controlled by controlling the current distribution. Also, such a current distribution can be controlled by changing the resistance value in the current path. According to the present invention, the current distribution is controlled by changing the contact resistance between the semiconductor layer and the electrode among various resistances in the current path.

Next, a method for changing the contact resistance between the semiconductor layer and the electrode will be described. First, an Sn layer, a Zn layer, and an Au layer are sequentially deposited on a semiconductor layer as a p-side electrode of a GaAlAs-based semiconductor laser, and this is heat-treated at 400 ° C. for about 10 to 15 minutes. At this time, various semiconductor laser devices were manufactured by changing the thickness of the Zn layer, and the device resistances were measured. FIG. 3 shows the results. The thicknesses of the Sn layer and the Au layer were constant at 150 ° and 2500 °, respectively. As is clear from the figure, the element resistance changes with the thickness of the Zn layer in the electrode, and takes the lowest value at 1850 °. Next, a current flowing through the element was measured for each element resistance value. The result is shown in FIG. In the figure, relative values with respect to the current flowing through the element when the thickness of the Zn layer is 1850 ° are shown.

From the above, it is possible to change the contact resistance between the electrode and the semiconductor layer by changing the layer thickness of the Zn layer by changing the p-side electrode to the three-layer structure of the Sn layer, the Zn layer, and the Au layer. Can be controlled.

Next, the device of the present invention utilizing the above principle will be described. First
The figure shows one embodiment of the device of the present invention, wherein (1) is a substrate made of n-type GaAs, (2) is an n-type cladding layer made of n-type Al _0.42 Ga _0.58 As and having a layer thickness of 1.5 μm, (3) ) Is undoped Al
An active layer made of _0.06 Ga _0.94 As and having a thickness of 0.07 μm,
(4) is a p-type cladding layer of p-type Al _0.42 Ga _0.58 A with a thickness of 1.2 μm, and (5) is a p-type GaAs with a layer thickness of 0.1 μm.
With a 6 μm cap layer, these layers are sequentially laminated on one main surface of the substrate (1). (6) is an insulating layer made of SiO ₂ deposited on the cap layer (5), and has a stripe-shaped opening (30 μm wide) in the center along the laser cavity direction (perpendicular to the paper). (W) in the figure is provided.
(7) is on the insulating layer (6) and the exposed cap layer (5)
On top, a Sn layer with a thickness of 150 mm, a Zn layer with a thickness of 1550 mm, and a layer thickness of 2500
The Au layer is a p-side first electrode on which a Au layer is deposited in this order. At the center thereof, a stripe-shaped opening (B in the figure) having a width of 14 μm is provided along the laser resonator direction by using a well-known photolithography technique. ing. (8) shows a Sn layer having a thickness of 150 ° and a layer thickness of 185 on the p-side first electrode (7) and the exposed cap layer (5).
The p-side second electrode is formed by depositing a Zn layer of 0 ° and an Au layer of 2500 ° in thickness in this order. Further, the p-side first electrode (7) and the p-side second electrode (8) are 400 ° C. after the deposition of the p-side second electrode (8).
For about 10 to 15 minutes. Reference numeral (9) denotes an n-side electrode formed on the other main surface of the substrate (1).

Thus, in the device of the present embodiment, the region W formed by the stripe-shaped openings of the insulating film (6) serves as a current path. Further, in the device of the present embodiment, in the width direction of the stripe-shaped opening, that is, in the region W, the region (A in the drawing) where the p-side first electrode (7) is in contact with the cap layer (5) and the p-side second electrode (8)
As described above, the contact resistance is different between the contact region (B in the drawing) and the region where B contacts. Further, in the device of this embodiment, the p-side second electrode (8) exists on the p-side first electrode (7). However, the p-side first electrode (7) has a sufficiently large thickness. The p-side second electrode (8) on the first electrode (7) does not affect the contact resistance with the cap layer (5). As a result, the region W of the device of this embodiment is
As shown in FIG. 2 (a), the gain is distributed at the center of the region W and low at the end.

Meanwhile, as shown in FIG. 2 (b), many higher-order modes can exist in addition to the basic mode in the region W which is the current path of the device of the present embodiment. However, since the device of this embodiment has a high gain distribution at the center of the region W as shown in FIG. 2A, the contribution of the gain to the higher-order mode showing a high light intensity distribution at the end of the region W Also, the contribution of the gain to the fundamental mode showing a high light intensity distribution at the center of the region W increases. As a result, oscillation in the higher-order mode is suppressed, and oscillation in only the fundamental mode is performed.

(G) Effects of the Invention According to the present invention, a first electrode portion that contacts a semiconductor layer in a current path at an end of the current path on the current path, and a central portion of the current path that contacts the semiconductor layer. A second electrode portion that is in contact with the first electrode portion, and a contact resistance between the first electrode portion and the semiconductor layer in the current path is higher than a contact resistance between the second electrode portion and the semiconductor layer. In a broad area laser in which the width of a passage permits oscillation in a higher-order transverse mode, oscillation in only the fundamental mode can be performed. Such an electrode can be easily formed by a well-known photolithography technique and two electrode deposition steps.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG.
FIG. 2B is a gain distribution diagram of the present embodiment device, FIG. 2B is a light intensity distribution diagram of a mode that can exist in the current path of the present embodiment device,
3 and 4 are characteristic diagrams for explaining the principle of the present invention.

Continuation of the front page (72) Nobuhiko Hayashi 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-55-91189 (JP, A) JP-A-59-67684 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01S 3/18

Claims (1)

(57) [Claims] 1. A broad area laser in which the width of a stripe-shaped current path extending along a laser resonator permits oscillation in a higher-order transverse mode, wherein the current path is formed on a semiconductor layer in the current path. A first contact at the end of the current path
An electrode portion, and a second electrode portion that is in contact with the semiconductor layer at a central portion of the current path, wherein a contact resistance between the first electrode portion and the semiconductor layer in the current path is reduced by the second electrode portion. A broad area laser characterized by having a contact resistance higher than the contact resistance with the semiconductor layer.