JPH0572116B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of Industrial Application This invention relates to a method for manufacturing a semiconductor laser,
More specifically, the present invention relates to a manufacturing method that can lower the forward voltage of a semiconductor laser.

(b) Prior Art For example, the following methods are known as conventional semiconductor laser manufacturing methods. This manufacturing method is
It is composed of the following steps.

: A first step in which a lower cladding layer, an active layer, a first upper cladding layer, a light absorption layer, and an evaporation prevention layer are deposited on the surface of a GaAs substrate introduced into a growth chamber of an MBE (molecular beam epitaxy) device. Growth process: This stacked GaAs substrate is taken out of the growth chamber and striped grooves are formed deep enough to reach the light absorption layer. Photoetching process: The GaAs substrate on which the striped grooves are formed is heated to select the light absorption layer. re-evaporation step: a second growth step in which a second upper cladding layer and a cap layer are deposited on the GaAs substrate on which the light absorption layer has been evaporated.

(c) Problems to be Solved by the Invention In the semiconductor laser manufactured by the above-mentioned conventional manufacturing method, the stripe grooves form the first upper cladding layer;
Although it is in contact with the second upper cladding layer, there is a problem in that an interface order occurs at the interface between the two, resulting in an increase in the forward voltage _VF .

It appears that this problem can be solved by increasing the carrier concentration of the first upper cladding layer. However, when the carrier concentration of the first upper cladding layer is increased, there is a problem that other characteristics such as the oscillation starting current I _th deteriorate.

The present invention was made in view of the above, and aims to provide a method for manufacturing a semiconductor laser with a low forward voltage V _F without impairing other characteristics.

(d) Means for Solving the Problems In order to solve the above problems, the method for manufacturing a semiconductor laser of the present invention comprises: forming a lower cladding layer, an active layer on the surface of a semiconductor substrate introduced into a growth chamber of an MBE apparatus; a first growth step of laminating and forming a first upper cladding layer, a light absorption layer, and an evaporation prevention layer; and a step of removing the laminated semiconductor substrate from the growth chamber to a depth reaching the light absorption layer. A photoetching process to form striped grooves, and a semiconductor substrate with these striped grooves formed.
A re-evaporation process in which the semiconductor substrate is introduced into the growth chamber of the MBE equipment and selectively evaporated by heating the semiconductor substrate, and a second upper cladding layer and a cap layer are added to the semiconductor substrate from which the light absorption layer has been evaporated. and a second growth step of depositing a second upper cladding layer, in which the carrier concentration of the second upper cladding layer is higher than the carrier concentration of the first upper cladding layer. , an evaporation prevention layer forming step of growing a second upper cladding layer and forming a second evaporation prevention layer on the cap layer of the semiconductor substrate after the second growth step; An annealing step in which the semiconductor substrate on which the layer has been formed is introduced into an annealing furnace and heated at a predetermined temperature for a predetermined time, and a second step in which the semiconductor substrate after this annealing is taken out from the annealing furnace and the second evaporation prevention layer is removed.
This method is characterized by the addition of an evaporation prevention layer etching step.

(e) Effect In the method for manufacturing a semiconductor laser of the present invention, in the annealing process, dopants diffuse from the second upper cladding layer to the first upper cladding layer, and the dopant diffuses into the first upper cladding layer.
The carrier concentration at the interface of the upper cladding layer increases, the series resistance component decreases, and the forward voltage V _F
goes down. On the other hand, in the portions other than the interface of the first upper cladding layer, the carrier concentration remains the same as before, so other characteristics such as the oscillation starting current I _th are not impaired.

In the annealing step, the semiconductor substrate is heated to a high temperature, so there is a risk that the cap layer and other layers may evaporate. Therefore, a second evaporation prevention layer forming step is provided before the annealing step, and the second evaporation prevention layer is formed to prevent the cap layer and the like from evaporating during the annealing step. This second evaporation prevention layer is unnecessary after the annealing process, so the second evaporation prevention layer is
It is removed in the evaporation prevention layer etching process.

(F) Embodiment An embodiment of the present invention will be described below based on the drawings.

●First growth step First, an N-type GaAs substrate 2 is prepared, and this substrate 2 is grown using molybdenum (Mo) in an MBE apparatus (not shown).
Mount it on the table. In the MBE equipment growth chamber, raw materials and impurities (dopants) introduced into the evaporation source are evaporated in the form of molecular beams. By controlling the shutter of the evaporation source of this molecular beam, the following layers 3 to 7 are successively grown (see FIG. 1).

That is, the lower cladding _layer 3 is made of N-type _{Al X} G _{a1-X A s} (X=0.6), Al
Active layer 4 consisting of P-type Al _X G _a1-X A _s (X=0.6)
First upper cladding layer 5 consisting of N-type GaAs
A light absorption layer 6 consisting of N-type Al _X G _a1-X A _s (X=
The evaporation prevention layer 7 consisting of 0.15) is sequentially laminated. Note that the value of the Al structure X shown above is an example and can be changed as appropriate.

●Photoetching process After the laminated GaAs substrate 2 is taken out from the growth chamber of the MBE apparatus, the evaporation prevention layer 7 is removed from the areas other than those where the stripe grooves are to be formed.
is covered with photoresist 8 (see FIG. 2). Then, the evaporation prevention layer 7 and the light absorption layer 6 are each etched to form stripe grooves 9 so that a small amount (for example, about 1000 Å) of the light absorption layer 6 remains.

●Re-evaporation process After removing the photoresist 8, the GaAs substrate 2 is introduced into the MBE growth chamber again, and while being irradiated with an As molecular beam, the GaAs substrate 2 is heated to a temperature of about 650°C to 850°C (preferably about 760°C). Heat it up. During this time, the impurities attached to the GaAs substrate evaporate, and the remaining light absorption layer 6 also evaporates, so that the first upper cladding layer 5 is exposed at the bottom of the stripe groove 9.

-Second Growth Step Next, a second upper cladding layer 10 is grown on the GaAs substrate 2 (see FIG. 3). This second upper cladding layer 10 is of P ⁺ type Al _Y G _a1-Y
A _s (for example, Al composition Y=0.6), and the carrier concentration is one order of magnitude higher than that of the first upper cladding layer 5. For example, if the carrier concentration of the first upper cladding layer 5 is 3×10 ¹⁷ cm ^-3 , the second
The carrier concentration of the upper cladding layer 10 is 3×
It is estimated to be about 10 ¹⁸ cm ^-3 .

The second upper cladding layer 10 subsequently contains P ⁺
A cap layer 11 made of type GaAs is laminated.

-Second Evaporation Prevention Layer Formation Process After the second growth process has been completed, the substrate 2 is left in the growth chamber of the MBE apparatus, and a second evaporation prevention layer 13 is grown on the cap layer 11. This second evaporation prevention layer 13 is made of Al _Z G _a1-Z
The _aluminum composition Z is, for example, 0.15.

Another step of forming the second evaporation prevention layer 13 is to take out the substrate 2 from the MBE growth chamber and introduce it into a CVD (Chemical Vapor Deposition) or PVD (Physical Vapor Deposition, evaporation, sputtering, etc.) apparatus. ,SiNx,
A thin film of SiO ₂ or the like can be formed as the second evaporation prevention layer 13.

In general, CVD or PVD equipment has higher processing capacity than MBE equipment, that is, it can process multiple substrates at once, so the latter process is preferable when mass production is required. . However, in addition to MBE equipment, CVD equipment or
PVD equipment is required and MBE equipment is required.
The latter cannot necessarily be said to be superior to the former, since it requires more effort to transfer the substrate to the CVD or PVD equipment.

●Annealing process Substrate 2 on which second evaporation prevention layer 13 is formed
is taken out from the MBE device (CVD device or PVD device) and introduced into an annealing furnace (not shown). Substrate 2 is heated to 650℃~800℃ in an annealing furnace.
It is heated to about ℃ and kept at that temperature for several minutes to several tens of minutes. During this time, the dopant diffuses from the second upper cladding layer 10 to the first upper cladding layer 5, and the upper cladding layer interface 5
The carrier concentration of a increases. On the other hand, the second evaporation prevention layer 13 prevents the cap layer 11 and the like from being evaporated and damaged.

- Second evaporation prevention layer etching step The substrate 2 that has been annealed is taken out of the annealing furnace, and the second evaporation prevention layer 13 is removed by etching. Thereafter, electrodes 12a and 12b are formed on the substrate 2 as in the conventional case.

In the thus obtained semiconductor laser 1, since the carrier concentration at the first upper cladding layer interface portion 5a is increased, the series resistance component can be suppressed.
Forward voltage V _F becomes lower. On the other hand, since the carrier concentration of the first upper cladding layer 5 other than the interface 5a remains the same as before, the oscillation starting current
Other properties such as I _th are not impaired.

(G) Effects of the Invention As explained above, in the method for manufacturing a semiconductor laser of the present invention, in the second growth step, the carrier concentration of the second upper cladding layer is lower than the carrier concentration of the first upper cladding layer. an evaporation prevention layer forming step of growing a second upper cladding layer so as to have a higher height, and forming a second evaporation prevention layer on the cap layer of the semiconductor substrate after the second growth step; The semiconductor substrate on which the second evaporation prevention layer is formed is introduced into an annealing furnace and heated at a predetermined temperature for a predetermined period of time. A second evaporation prevention layer etching step is added. Therefore, there is an advantage that a semiconductor laser with a lower forward voltage V _F can be manufactured without impairing other characteristics such as the oscillation start current I _th .

[Brief explanation of the drawing]

FIG. 1, FIG. 2, FIG. 3, FIG. 4, and FIG. 5 are diagrams for explaining the 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, 6: light absorption layer, 7: first evaporation prevention layer, 9: stripe groove,
10: second upper cladding layer, 11: cap layer, 13: second evaporation prevention layer.

Claims (1)

[Claims] 1. A lower cladding layer, an active layer, a first upper cladding 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. a first growth step; a photoetching step in which the stacked semiconductor substrates are taken out of the growth chamber and striped grooves with a depth reaching the light absorption layer are formed; and the semiconductor substrate on which the striped grooves have been formed is
A re-evaporation process in which the semiconductor substrate is introduced into the growth chamber of the MBE equipment and selectively evaporated by heating the semiconductor substrate, and a second upper cladding layer and a cap layer are added to the semiconductor substrate from which the light absorption layer has been evaporated. and a second growth step of laminating a semiconductor laser, wherein in the second growth step, the carrier concentration of the second upper cladding layer is equal to the carrier concentration of the first upper cladding layer. a step of forming a second evaporation prevention layer on the cap layer of the semiconductor substrate after the second growth step; The semiconductor substrate on which the second evaporation prevention layer is formed is introduced into an annealing furnace and heated at a predetermined temperature for a predetermined time. 2nd to remove
1. A method for manufacturing a semiconductor laser, comprising the step of etching an evaporation prevention layer. 2 The step of forming the second evaporation prevention layer includes forming the second evaporation prevention layer.
2. The method of manufacturing a semiconductor laser according to claim 1, wherein the semiconductor substrate is kept in a growth chamber of an MBE apparatus after the growth step is completed, and the second evaporation prevention layer is grown by MBE. 3 The second evaporation prevention layer forming step includes the second evaporation prevention layer forming step.
The semiconductor laser according to claim 1, wherein after the growth step is completed, the semiconductor substrate is taken out of the MBE apparatus growth chamber, introduced into a CVD apparatus or PVD apparatus, and a second evaporation prevention layer is formed by CVD or PVD. manufacturing method.