JPH0137873B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of Industrial Application This invention relates to a method of manufacturing a semiconductor laser,
In particular, the present invention relates to a method of manufacturing an AlGaAs semiconductor laser manufactured using an MBE apparatus.

(b) Prior Art In the method for manufacturing this type of semiconductor laser, the case of manufacturing a semiconductor laser having a structure that requires, for example, two MBE growth steps will be described below, and
Point out the problem.

First, after forming a first growth layer in the first MBE growth process, the semiconductor substrate is taken out from the MBE apparatus, and a stripe groove of a predetermined width and a depth reaching the first upper cladding layer is formed in a photoetching process. Form. As this photoetching step is performed, impurities such as oxides are directly attached to the etched portion (the surface of the first upper cladding layer), so these impurities are evaporated by a predetermined method. After that, in the second MBE growth process, the second
Stack the growth layers.

Therefore, in the step of evaporating the impurities, if the Al composition of the first upper cladding layer is 0.4 or more, the impurities such as the oxides are difficult to evaporate. Therefore, the stacked state of the second growth layer formed in the second growth step deteriorates, causing a problem that current no longer flows through this portion. On the other hand, if the Al composition of the first upper cladding layer is set to 0.4 or less,
Although the stacked state of the second grown layer is relatively good, on the other hand, a problem arises in that the light confinement efficiency decreases. Based on these factors, it is difficult to manufacture semiconductor lasers with good electrical and optical properties using conventional methods.

(c) Purpose This invention improves the stacking state of the second grown layer regardless of the Al composition value of the first upper cladding layer,
It is an object of the present invention to provide a method for manufacturing a semiconductor laser that can easily manufacture a semiconductor laser with good electrical and optical properties.

(D) Structure The method for manufacturing a semiconductor laser according to the present invention is characterized by forming a first growth layer in the first growth step, and leaving a light absorption layer as appropriate in the next etching step. A stripe groove is formed by deep etching so that the first upper cladding layer is not exposed, and a part or all of the remaining light absorption layer and the surface protection layer which is the top layer of the first growth layer are removed by a thermal cleaning process. The second growth layer was formed in the second growth step.

(E) Embodiment FIG. 1 is an explanatory diagram showing an embodiment of the method for manufacturing a semiconductor laser according to the present invention.

(a) N-type installed in the MBE device (not shown)
A semiconductor substrate 10 made of GaAs is heated by a predetermined method. The raw materials contained in the evaporation sources are evaporated in the form of molecular beams. By monitoring this raw material with a mass spectrometer (not shown ₎ and controlling the temperature and shutter of the evaporation source with a computer _{(not shown} ), the lower cladding layer 21 (Al composition = 0.55) and _Al
Active layer 22 made of Ga _1-X As (Al composition X=
0.12), the first upper cladding layer 23 made of P-type Al _x Ga _1-x As (Al composition X = 0.55), and the N-type
A light absorption layer 24 made of GaAs and an N-type Al _x Ga _1-x
Evaporation prevention layer 25 made of As (Al composition x = 0.35)
and a surface protective layer 26 made of non-doped GaAs.
The first growth layer 20 is formed by sequentially laminating the
(first growth step).

(b) Semiconductor substrate 10 on which first growth layer 20 is formed
After taking out the semiconductor substrate 10 from the MBE apparatus, the back surface of the semiconductor substrate 10 is wrapped. Next, through photoresist coating, exposure, and development steps, the surface protective layer 26 other than the portion where the stripe grooves are to be formed is covered with a photoresist 60. This photoresist 6
0 as a mask, the surface protection layer 26, evaporation prevention layer 25, and light absorption layer 24 are selectively etched to a depth such that the light absorption layer 24 remains at an appropriate depth (for example, approximately 1000 Å) to form stripe grooves 30 (etching). process). Note that photolithography technology is used in this embodiment.

(c) The semiconductor substrate 10 from which the photoresist 60 has been removed is organically cleaned. After that, the semiconductor substrate 10 is mounted again into the MBE apparatus. here,
The semiconductor substrate 10 is heated at about 740° C. while applying an arsenic molecular beam to the semiconductor substrate 10. As it is, about
By performing the etching for 20 minutes, impurities etc. attached in the etching process are evaporated, and furthermore, part or all of the remaining light absorption layer 24 and surface protection layer 26 are evaporated (thermal cleaning process). Note that this exposes the surface of the first upper cladding layer 23 above the stripe grooves, but
Since the process is carried out inside the MBE equipment, there is no need to worry about impurities adhering to it.

(d) In the state of step (c), the temperature of the semiconductor substrate 10 is set to about 600°C, and a second upper cladding layer made of P-type Al _Y Ga _1-Y As is formed by the same method as in step (a). 41 (Al composition Y = 0.35) and P ⁺ type GaAs
A second growth layer 40 is formed by sequentially stacking a cap layer 42 consisting of the following (second growth step). Thereafter, a P-type electrode 50 and an N-type electrode 51 are formed in the same manner as in a normal semiconductor laser manufacturing method.

Figure 2 is an explanatory diagram showing the relationship between temperature and evaporation rate in AlGaAs and GaAs. According to the figure, when the temperature is increased, AlGaAs (first upper cladding layer 23) hardly evaporates, but GaAs (light absorption The evaporation rate of the layer 24) increases as the temperature increases. In other words, it can be said that when GaAs is evaporated, there is almost no effect on AlGaAs located below.

In this example, since the Al composition of the lower cladding layer 21 and the first upper cladding layer 23 was set to 0.55,
The lower cladding layer 21 and the first upper cladding layer 2
It is possible to improve the light confinement effect with 3.

In addition, in the above example, Al _X Ga _1-X As and
Although the Al composition of each layer made of Al _Y Ga _1-Y As is shown, the invention is not limited to this, and it goes without saying that it can be changed as appropriate.

Furthermore, the surface protective layer 26 and the remaining light absorption layer 24 of GaAs provide a passivation effect to the entire surface _of the semiconductor substrate, _and Al _Y
The above method of regrowing Ga _1-Y As is not limited to manufacturing semiconductor lasers, but can of course be applied to other semiconductor devices.

(F) Effect This invention produces a passivation effect on the entire surface of the semiconductor substrate using the light absorption layer left on the top of the stripe groove formed in the etching process and the surface protection layer that is the top layer of the first growth layer. Because I have it,
In the etching process, it is possible to prevent impurities from directly adhering to the surfaces of the first upper cladding layer and the evaporation prevention layer. Moreover, in the thermal cleaning process, the entire surface of the semiconductor substrate is cleaned by evaporating part or all of the remaining light absorption layer and surface protective layer, so the Al composition value of the first upper cladding layer is not affected. Therefore, the stacked state of the second grown layer can be improved.

Therefore, the present invention has a significant effect in that it does not require particularly high-precision technology and does not require an increase in the number of steps. That is, it has become possible to easily manufacture a semiconductor laser with good electrical and optical properties.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the method for manufacturing a semiconductor laser according to the present invention, and FIG. 2 is an explanatory diagram showing the relationship between temperature and evaporation rate of AlGaAs and GaAs. 10... Semiconductor substrate, 20... First growth layer, 2
1... lower cladding layer, 22... active layer, 23...
...first upper cladding layer, 24...light absorption layer, 25
... Evaporation prevention layer, 26 ... Surface protective layer, 30 ...
Stripe groove, 40...second growth layer, 41...second upper cladding layer, 42...cap layer.

Claims (1)

[Claims] 1. A method for manufacturing an AlGaAs semiconductor laser manufactured using an MBE apparatus, comprising: a lower cladding layer, an active layer, a first upper cladding layer, a light absorption layer made of GaAs, and an evaporation prevention layer. and a surface protection layer made of GaAs on the surface of the semiconductor substrate, and an etching step to form a stripe groove of a desired width and depth to leave the light absorption layer as appropriate. , reintroducing the semiconductor substrate on which the stripe grooves have been formed into the growth chamber, and bombarding the semiconductor substrate with arsenic while heating the semiconductor substrate;
a thermal cleaning step of evaporating part or all of the remaining light absorption layer and the surface protection layer that is the top layer of the semiconductor substrate; and forming a second upper cladding layer and a cap layer on the thermally cleaned surface of the semiconductor substrate. and a second growth step of sequentially stacking.