JPH0632337B2 - Method for manufacturing semiconductor laser - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor laser.

(B) Conventional Technology In recent years, many semiconductor lasers having a stripe structure have been developed. A typical one is a laser having an inner stripe structure shown in FIG. 2 (for example, Appl.phys.Lett.40 (5), 1 March 1982. 372).
Pages to page 374). In the figure, (1) is a P-type substrate, (2) is an inverted mesa stripe formed on the surface of the substrate, (3) is an N-type block layer formed on both sides of the stripe, and (4) to (7) ) Are the P-type first clad layer, the active layer, the N-type second clad layer and the cap layer, which are sequentially laminated on the stripe (2) and the block layer (3) respectively, and (8) and (9) are the P side, respectively. An electrode and an N-side electrode.

The block layer (3) acts as a current constriction layer, for which purpose it occurs in the active layer (5) and the block layer (3)
It is necessary to ensure that the minority carriers generated in the block layer due to the photons incident on the recombination disappear in the block layer (3). Therefore, the blocking layer (3) must have a thickness that is at least greater than the diffusion length of minority carriers.

In the above structure, it is not easy to increase the thickness of the block layer (3). Because in this case, the inverted mesa stripe (2) created by etching after forming the block layer
However, in such a deep etching process, the amount of side etching becomes large. As a result, the aperture width of the stripe (2) undesirably increases, and a laser beam in a predetermined mode cannot be obtained.

On the other hand, the diffusion distance of a few carriers can be shortened by increasing the impurity concentration of the block layer, but when such a high impurity concentration layer is formed by liquid phase epitaxial growth,
There is a problem with the flatness of the grown layer.

Therefore, in the above conventional structure, the thickness of the block layer is 0.
The carrier concentration is set to 6 to 1.0 μm and the carrier concentration is set to 2 to 6 × 10 ¹⁸ cm ⁻³ , respectively. However, it is difficult to uniformly grow such a thin block layer on the entire surface of the wafer-substrate. ,
Further, such a high density includes the above-mentioned problem of flatness.

(C) Problems to be Solved by the Invention The present invention provides a method for easily manufacturing a semiconductor laser having a block layer having a sufficiently large thickness.

(D) Means for Solving the Problems The method of the present invention comprises a step of forming a mesa stripe on the surface of a first conductive type semiconductor substrate, and a thin mesa stripe on the surface of the substrate on which the mesa stripe is formed. And forming a second conductive type block layer thick on the surface of the substrate other than on the mesa stripe by a liquid phase epitaxial growth method,
A step of forming a groove reaching the mesa stripe by removing only a central portion of the thin block layer formed on the mesa stripe by etching; and a first clad layer, an active layer, and a second layer on the block layer and the groove. Forming a clad layer in this order.

(E) Operation According to the present invention, the block layer to be deposited is thin on the mesa stripes and thicker in other areas. Therefore, by appropriately determining the height of the mesa stripes, it is possible to obtain a sufficient thickness. A block layer for current confinement can be obtained, and a groove having a sufficiently narrow opening width can be easily formed on the mesa stripe.

(F) Example FIGS. 1A to 1E show the method of this example in the order of steps. Although only one chip is shown in the same drawing, in reality, many chips are simultaneously formed on a single wafer-substrate.

In the first step shown in FIG. 1A, Zn-doped 1
A P-type GaAs substrate (10) having a carrier concentration of × 10 ¹⁹ cm ^-3 is prepared. In the second step shown in FIG. 1B, the mesa stripes (11) are formed on the surface of the substrate (10) by selective etching. The height h of this mesa stripe is 1.7μ
m, the lower width w ₁ is 10 μm, and the upper width w ₂ is 5 μm.

In the third step shown in FIG. 1C, an N-type GaAs block layer (12) is formed on the surface of the substrate (10) by a liquid phase epitaxial growth method. At this time, the dopant is Te and its concentration is 1
It is × 10 ¹⁷ to 1 × 10 ¹⁸ cm ^-3 . Block layer formed (1
The thickness of 2) is thin on the mesa stripe 11 and thick on the other substrate surface (2 μm in this embodiment).

In the fourth step shown in FIG. 1D, the mesa stripe (11)
Only the central portion of the block layer deposited above is removed to form a groove (13) reaching the mesa stripe (11). Groove (13)
Has an inverted mesa shape and its upper opening width w ₃ is ₃ to 4μ.
m, and the groove depth is 0.8 μm. The groove 13 may have a V-shaped cross section. Although the groove (13) is formed by etching, since the thickness of the block layer on the mesa stripe (11) is thin, there is no influence of side etching and a groove having an accurate opening width can be obtained.

In the final step shown in FIG. 1E, the P-type clad layer (14), the active layer (15), the N-type second clad layer (16) and the N-type cap are formed on the block layer (12) and the groove (13). The layers (17) are sequentially formed by the liquid phase epitaxial growth method, and finally, the P-side electrode (1
8) and the N-side electrode (19) are formed respectively. This final step itself is carried out by a well-known method, but the first cladding layer (14) is 1 × 10 ¹⁷ to 1 × 10 ¹⁸ cm ⁻³ Zn-doped Ga.
It is made of 0.5Al0.5As and is 1.0-1.
3 μm, 0.2 to 0.5 μm in other flat parts
The thickness of the active layer (15) is undoped Ga0.85Al0.
The second cladding layer (16) is composed of 15 As and has a thickness of 0.1 μm, and the second cladding layer (16) is 1 × 10 ¹⁷ to 1 × 10 ¹⁸ cm ⁻³ Te-doped Ga0.5Al0.5.
Cap layer consisting of As and having a thickness of 1-2 μm (17)
Is made of 1 × 10 ¹⁸ cm ⁻³ Te-doped GaAs and has a thickness of 1 to ³ μm.

According to the method of the embodiment described above, the thickness of the block layer (12) can be made sufficiently large, so that the current constricting action of the block layer can be uniformly and surely obtained. Specifically, the laser produced by the method of the above embodiment has a threshold current of 2
At 0 to 30 mA, 92% of the total number of chips produced from a single wafer was in this range, and the yield was increased by 22% compared to 70% of the conventional method shown in FIG. Also, groove (13)
Since the aperture width of is also accurately set, a desired laser beam mode can be obtained with high yield.

The method of the present invention can be applied to materials other than the materials of the above embodiment, and the conductivity types of the substrate (10) and other layers of the embodiment can be reversed.

(G) Effect of the Invention According to the present invention, a step of forming a mesa stripe on the surface of a first conductive type semiconductor substrate, and a thin mesa stripe on the surface of the substrate on which the mesa stripe is formed and the mesa stripe And a step of forming a thick second conductive type block layer on the surface of the substrate other than by a liquid phase epitaxial growth method,
A step of forming a groove reaching the mesa stripe by removing only a central portion of the thin block layer formed on the mesa stripe by etching; and a first clad layer, an active layer, and a second layer on the block layer and the groove. Since the step of forming the clad layer in this order is included, a semiconductor laser having a block layer having a sufficiently large thickness can be easily manufactured without any trouble, and the manufacturing yield is significantly improved. . In addition, the opening width of the groove can be set to a desired value with which a laser beam in a predetermined mode can be obtained with high accuracy, and
The width of the current path is the groove width on the top surface of the mesa stripe, and the current can be sufficiently narrowed.

[Brief description of drawings]

1A to 1E are side views by process showing an embodiment of the present invention.
FIG. 2 is a side view showing a conventional example. (10) …… Substrate, (11) …… Mesa stripe, (12) …… Block layer, (13) …… Groove.

Claims (1)

[Claims] 1. A step of forming a mesa stripe on the surface of a first conductive type semiconductor substrate, and a step of forming thin on the mesa stripe on the surface of the substrate on which the mesa stripe is formed and thick on the surface of the substrate other than the mesa stripe. A step of forming a second conductive type block layer by a liquid phase epitaxial growth method, and a step of removing only a central portion of the thin block layer formed on the mesa stripe by etching to form a groove reaching the mesa stripe. And a step of forming a first clad layer, an active layer, and a second clad layer on the block layer and the groove in this order, a method of manufacturing a semiconductor laser.