JPH0656911B2 - Semiconductor laser manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor laser, and more particularly to a method for manufacturing a semiconductor laser having a low forward voltage.

(B) Conventional Technology As a conventional method for manufacturing a semiconductor laser, for example, the following method is known. This manufacturing method includes the following steps i to iv.

i: A lower clad layer, an active layer, a first upper clad layer, a light absorption layer and an evaporation prevention layer are laminated on the surface of a GaAs substrate introduced into a growth chamber of an MBE (Molecular Beam Epitaxy) apparatus. First growth step ii: The stacked GaAs substrate is taken out of the growth chamber, and a photo-etching step is performed to form a stripe groove having a depth reaching the light absorption layer. Iii: The GaAs substrate having the stripe groove is heated. Re-evaporation step of selectively evaporating the light absorption layer by means of iv: a second growth step of laminating a second upper cladding layer and a cap layer on the GaAs substrate in which the impurities are evaporated.

(C) Problem to be Solved by the Invention In the semiconductor laser manufactured by the above-described conventional manufacturing method, the first upper clad layer and the second upper clad layer are in contact with each other at the stripe groove, but the interface (current There is a problem in that the interface order occurs in the narrowed portion) and the forward voltage V _F becomes high.

It seems that this problem can be solved by increasing the carrier concentration of the first upper cladding layer. However, if the carrier concentration of the first upper cladding layer is increased,
There is a problem that other characteristics such as the oscillation start current I _th are deteriorated.

This invention has been made in view of the above, without impairing the other properties, has an object to provide a method of manufacturing a low semiconductor laser forward voltage V _F.

(D) Means for Solving the Problems In order to solve the above problems, a method for manufacturing a semiconductor laser according to the present invention is directed to a semiconductor substrate introduced into a growth chamber of an MBE apparatus. A first growth step of stacking a first upper clad layer, a light absorption layer, and an evaporation prevention layer; and a stripe having a depth reaching the light absorption layer by taking out the stacked semiconductor substrate from the growth chamber. A photo-etching step of forming a groove; a re-evaporation step of introducing the semiconductor substrate having the stripe groove formed therein into a growth chamber of an MBE apparatus and heating the semiconductor substrate to selectively evaporate the light absorption layer; A second growth step of stacking a second upper clad layer and a cap layer on a semiconductor substrate from which impurities have been evaporated, wherein the second upper step is performed in the second growth step. The carrier concentration of the first upper clad layer is made higher than that of the first upper clad layer, and the semiconductor substrate is heated in the MBE apparatus growth chamber for a predetermined time after the growth of the second upper clad layer and before the cap layer growth. Then, in the first upper cladding layer,
It is characterized in that the interface portion with the second upper cladding layer has a high carrier concentration.

(E) Action In the method of manufacturing a semiconductor laser of the present invention, since the carrier concentration of the second upper cladding layer is increased, when the heating is performed for a predetermined time, the second upper cladding layer is more than the first upper cladding layer. The dopant diffuses into. For this reason,
The carrier concentration increases only at the interface of the first upper clad layer, the series resistance component decreases, and the forward voltage V _F decreases.
However, since the carrier concentration in the first upper clad layer is high only in the interface portion, there is little risk of damaging other characteristics such as the oscillation start current I _th .

(F) Embodiment An embodiment will be described below based on an embodiment.

First Growth Step First, the N-type GaAs substrate 2 mounted on the molybden table is introduced into the MBE apparatus growth chamber. In the growth chamber of the MBE apparatus, the raw material and impurities (dopants) put in the evaporation source are evaporated in the form of molecular beam. By controlling the shutter of the evaporation source, the following layers 3 to 7 are sequentially grown (first
See figure).

Ie, N-type _{Al X G a1-X A s} (X = 0.6) lower cladding layer 3 made _{of, Al X G a1-X A} s (X = 0.15)
Become more active layer 4, P-type _{Al X G a1-X A s} (X = 0.
The first upper cladding layer 5, a light absorbing layer made of N-type GaAs 6, N-type made of _{6) Al X G a1-X} A s (X = 0.1
The evaporation prevention layer 7 composed of 5) is sequentially laminated. The value of the Al structure X shown above is an example and can be changed as appropriate.

Photo-etching step After the laminated GaAs substrate 2 is taken out from the growth chamber of the MBE apparatus, the evaporation preventing layer 7 other than the portion where the stripe groove is to be formed is covered with the photoresist 8 (see FIG. 2). . Then, the evaporation preventing layer 7 and the light absorbing layer 6 are etched to form the stripe grooves 9 so that the light absorbing layer 6 is slightly left (for example, about 1000 Å).

・ Re-evaporation process After removing the photoresist 8, the GaAs substrate 2 is re-evaporated.
Introduced into the BE equipment growth chamber, G
The aAs substrate 2 is heated at a temperature of about 650 ° C to 850 ° C. During this time, the impurities adhering to the GaAs substrate are evaporated, and the remaining light absorption layer 6 is also evaporated so that the first upper cladding layer 5 is exposed at the bottom of the stripe groove 9.

Second growth step Next, the second upper cladding layer 10 is formed on the GaAs substrate 2.
Are grown (see FIG. 3). The second upper cladding layer 10 is made of ^{P +} -type _{Al Y G a1-Y A s} ( for example, Al composition Y = 0.6), the carrier concentration than the first upper cladding layer 5 order of magnitude higher Has been done. For example, the first upper carrier concentration of the cladding layer 5 if the 3 × 10 ¹⁷ cm ^-3, the second 3 carrier concentration of the upper cladding layer of × 10 ¹⁸
It is about cm ^-3 .

When the growth of the second upper cladding layer 10 is completed, G
The temperature of the aAs substrate 2 is raised to 650 ° C. to 850 ° C. (preferably about 760 ° C.) and kept as it is for several minutes to several tens minutes (annealing). During this time, the dopant diffuses from the second upper clad layer 10 to the first upper clad layer 5, and the carrier concentration in the upper clad layer interface 5a increases.

When the annealing is completed, the cap layer 11 made of P ⁺ -type GaAs is grown on the second upper cladding layer 10 and the electrodes 12a and 12b are formed in the same manner as in the prior art (see FIG. 4).

In the semiconductor laser 1 thus obtained, the carrier concentration in the first upper cladding layer interface 5a is increased,
The series resistance component can be suppressed, and the forward voltage V _F becomes low. On the other hand, since the carrier concentration of the portion other than the interface portion 5a of the first upper cladding layer 5 is the same as the conventional one, other characteristics such as the oscillation start current I _th are not deteriorated.

(G) Effect of the Invention As described above, in the method for manufacturing a semiconductor laser of the present invention, the carrier concentration of the second upper cladding layer is made higher than the carrier concentration of the first upper cladding layer in the second growth step. After the growth of the second upper clad layer, the semiconductor substrate is heated in the growth chamber of the MBE apparatus for a predetermined time after the growth of the second upper clad layer to form the second upper clad layer of the first upper clad layer. Is characterized by having a high carrier concentration at the interface portion of, so that there is an advantage that a semiconductor laser having a low forward voltage V _F can be obtained without impairing other characteristics such as the oscillation start current I _th. . Further, there is an advantage that the dopant can be diffused from the second upper clad layer to the first upper clad layer in the MBE apparatus growth chamber.

[Brief description of drawings]

1, 2, 3, and 4 are views for explaining a manufacturing process of a semiconductor laser according to an embodiment of the present invention. 2: GaAs substrate, 3: lower cladding layer, 4: active layer, 5: first upper cladding layer, 5a: interface portion, 6: light absorption layer, 7: evaporation preventing layer, 9: stripe groove, 10: first 2 upper clad layer, 11: cap layer.

Claims (1)

[Claims] 1. A first clad layer in which a lower clad layer, an active layer, a first upper clad layer, a light absorption layer and an evaporation prevention layer are laminated on the surface of a semiconductor substrate introduced into a growth chamber of an MBE apparatus. And a photoetching step of taking out the stacked semiconductor substrate from the growth chamber and forming a stripe groove having a depth reaching the light absorption layer, and the semiconductor substrate having the stripe groove formed in an MBE apparatus. A re-evaporation step of introducing into the growth chamber and heating the semiconductor substrate to selectively evaporate the light absorption layer, and stacking a second upper clad layer and a cap layer on the semiconductor substrate having the light absorption layer evaporated In the method of manufacturing a semiconductor laser, the carrier concentration of the second upper clad layer is changed to the carrier concentration of the first upper clad layer in the second growing step. After the second upper clad layer is grown at a higher temperature, the semiconductor substrate is heated in the growth chamber in the MBE apparatus for a predetermined time after the growth of the second upper clad layer and the second upper clad layer of the second upper clad layer. A method of manufacturing a semiconductor laser, characterized in that an interface portion with an upper clad layer has a high carrier concentration.