JPH0740618B2 - Semiconductor laser and manufacturing method thereof - Google Patents

Description

The present invention relates to a semiconductor laser having an AlGaAs double heterojunction structure which requires two MBE growth steps and a method for manufacturing the same.

(B) Prior Art A method of manufacturing a semiconductor laser having a structure that requires two MBE growth steps will be described below and its problems will be pointed out.

First, after stacking the first growth layer on the surface of the substrate in the first MBE growth step, the substrate is taken out from the MBE apparatus and a stripe groove reaching the first upper cladding layer is formed in the etching step. With this etching process,
Since impurities such as oxides are directly attached to the etched portion, the impurities are evaporated by a predetermined method. Then, the second growth layer is laminated in the second MBE growth step.

Thus, in the step of evaporating the impurities, the first
When the A1 composition of the upper clad layer is 0.4 or more, the impurities are less likely to be evaporated. As a result, the laminated state of the second growth layer deteriorates, causing a problem that current does not flow through this portion. On the other hand, if the A1 composition of the first upper cladding layer is 0.4 or less, the laminated state of the second growth layer will be good, but there will be a problem that the light confinement efficiency will be reduced.

(C) Object The first invention aims to provide a semiconductor laser having improved electrical and optical properties.

It is an object of the second invention to provide a method of manufacturing a semiconductor laser which can manufacture the shape of a semiconductor laser having the above characteristics with good reproducibility and can be easily manufactured, and which can improve the manufacturing yield.

(D) Configuration The semiconductor laser according to the first invention is characterized in that a lower clad layer made of AlGaAs of the same conductivity type as that of the substrate is sequentially laminated on the surface of a GaAs substrate of one conductivity type.
_x Ga _1-x As active layer and Al of opposite conductivity type to the substrate
A first upper clad layer made of GaAs; a protective layer made of GaAs having a conductivity type opposite to that of the substrate and having a film thickness equal to or larger than that of the active layer due to a quantum effect and having a conductivity type opposite to that of the substrate; A conductive type AlGaAs layer and a current limiting layer made of the same conductive type GaAs as the substrate constitute a first growth layer, and the first growth layer has a depth such that the surface of the protective layer is exposed. A second groove made of AlGaAs, which has a taper surface narrowing toward the substrate side and is formed along the laser resonator wavelength, is laminated on the first growth layer, and has a conductivity type opposite to that of the substrate. The upper clad layer and the cap layer for improving ohmic contact make the second
This is because the growth layer was constructed.

A feature of the method for manufacturing a semiconductor laser according to the second invention is that one surface of a substrate made of GaAs of conductivity type has an AlGaAs lower clad layer of the same conductivity type as the substrate and Al _x Ga _1-x. As
Made of AlGaAs, a first upper cladding layer made of AlGaAs having a conductivity type opposite to that of the substrate, and a film thickness set to have a bandgap equal to or greater than that of the active layer due to a quantum effect and having a conductivity opposite to that of the substrate. Growth step of stacking a first growth layer including a protective layer made of GaAs of the same type, an AlGaAs layer of the same conductivity type as the substrate, and a current limiting layer made of GaAs of the same conductivity type as the substrate And selectively etching only the current limiting layer with a solution having an etching rate of GaAs >> AlGaAs.
s >> A stripe groove having a taper surface with a depth that exposes the surface of the protective layer and narrows toward the substrate side by selectively etching only the AlGaAs layer with a solution having an etching rate of GaAs And a thermal cleaning step of evaporating impurities attached by the etching step by heating the substrate while applying an arsenic molecular beam to the first growth layer in which the stripe groove is formed, Stacking a second growth layer composed of a second upper cladding layer made of AlGaAs having a conductivity type opposite to that of the substrate and a cap layer for improving ohmic contact on the cleaned first growth layer; It has two growth steps.

(E) Embodiment First Invention FIG. 1 is a perspective view showing an embodiment of a semiconductor laser according to the first invention. In the figure, 1 is a semiconductor laser, and 1a and 1b are Fabry-Perot reflecting surfaces. 10 is a substrate made of N-type GaAs, 21 is N-type Al _x Ga _1-x As (A1 composition x
= 0.55) and 22 is Al _x Ga _1-x As
An active layer composed of (Al composition _x 0.12) and 23 are P-type Al _x Ga _1-x A
s (A1 composition x = 0.55) first upper cladding layer, 24
Is an AlGaAs layer made of P-type GaAs, 26 is a current limiting layer made of N-type GaAs, 41 is a second upper cladding layer made of P-type Al _y Ga _1-y As (A1 composition y = 0.55), and 42 is P ^A cap layer made of ⁺ type GaAs, 50 is a P type electrode, and 51 is an N electrode. The protective layer 24 is set to have a film thickness equal to or larger than that of the active layer 22 due to the quantum effect.

More specifically, the lower clad layer 21, the active layer 22, the first upper clad layer 23, the protective layer 24, the AlGaAs layer 25, and the current limiting layer 26 constitute the first growth layer 20. The first growth layer 20 has a stripe groove 30 having a tapered surface 31 having a depth at which the surface of the protective layer 24 is exposed and narrowing toward the substrate 10.
Are formed along the laser cavity wavelength of the semiconductor laser 1. And the second upper clad layer 41 and the cap layer
The second growth layer 40 is constituted by 42 and. This second growth layer
The reference numeral 40 is a recessed shape corresponding to the shape of the stripe groove 30, and is stacked on the first growth layer 20.

Then, the stripe groove of the semiconductor laser 1 as described above is
The band structure at the center of 30 is as shown in FIG. In FIG. 2, A is the conduction band, B is the forbidden band, and C is the valence band. According to FIG.
It can be seen that the band gap of is wider than that of the active layer 22.

This is because the quantum well structure is formed by the first upper clad layer 23 and the second upper clad layer 41, and the substantial band gap of the protective layer 24 increases due to the thickness of the quantum well. .

In the first place, the presence of the absorption layer in the semiconductor laser not only deteriorates the optical properties, but also increases the operating current and deteriorates the electrical properties.

However, since the bandgap of the protective layer 24 is made larger than that of the active layer 22 here, the light emitted from the active layer 22 is not absorbed by the protective layer 24, and the increase in operating current can be suppressed.

Therefore, there is a merit in improving the optical and electrical properties of the semiconductor laser.

Second Invention FIG. 3 is a reference diagram for explaining a method for manufacturing a semiconductor laser according to the second invention, and description will be given below with reference to the same figure.

(A) The substrate 10 mounted in an MBE device (not shown) is heated by a predetermined method. The raw materials and impurities stored in the evaporation sources are evaporated in the form of molecular beams. By monitoring these raw materials with a mass spectrometer (not shown) and controlling the temperature of the evaporation source and the shutter with a computer (not shown),
The first growth layer 20 is laminated (first growth step). In addition,
The thickness of the protective layer 24 is about 30 to 40Å, and the thickness of the AlGaAs layer 25 is 10
It is assumed that the current limiting layer 26 is set to about 0Å and the current limiting layer 26 is set to about 500 to 5000Å.

(B) After taking out the substrate 10 on which the first growth layer 20 is laminated from the MBE device to the outside, the back surface of the substrate 10 is lapped. Next, the current limiting layer 26 other than the portion where the stripe groove is to be formed is covered with a photoresist 60. The current limiting layer 26 is selectively etched by immersing the substrate 10 using the photoresist 60 as a mask in a solution having an etching rate of GaAs >> AlGaAs, so that the surface of the AlGaAs layer 25 is exposed to the depth of the substrate side. A stripe groove 30 having a tapered surface narrowing toward the first growth layer 20 is formed (etching step). As the solution, for example, an H ₂ O ₂ (30%) aqueous solution whose pH is adjusted to 7.04 with NH ₄ OH is used. The AlGaAs layer
25 serves as a stop layer when the current limiting layer 26 is selectively etched.

(C) The substrate 10 from which the photoresist 60 has been removed is organically washed, and the exposed AlGaAs layer 25 is selectively etched by using, for example, HCl, whereby the stripe groove 30 is formed.
To a depth at which the surface of the protective layer 24 is exposed.

(D) The substrate 10 is mounted in the MBE device again. Here, by heating the substrate 10 while applying the arsenic molecular beam to the substrate 10, impurities such as oxides attached in the etching process are evaporated (thermal cleaning process).
However, the heating temperature and time are the same for the protective layer 24 made of GaAs
Shall not evaporate.

This is to prevent excessive thermal cleaning. The heating temperature and time of the substrate are determined as follows.

Table 1 is a diagram showing the relationship between the substrate temperature and the evaporation rate of GaAs. For example, if the substrate temperature is set to 720 ° C, G
Since the evaporation rate of aAs is 0.5 μm / h, if thermal cleaning is performed for 10 minutes, evaporation will proceed by about 80Å.
If the protective layer 24 is 30 Å to 40 Å, it will be completely evaporated, resulting in damage to the substrate. Therefore, in this case, it is necessary to shorten the thermal cleaning time or lower the temperature of the substrate.

As described above, the optimum substrate heating temperature and time are determined after the relationship between the substrate temperature and the GaAs evaporation rate is obtained in advance so as not to damage the substrate as much as possible.

In the steps (e) and (d), the temperature of the substrate 10 is set to about 600 ° C., and the second growth layer 40 is laminated on the first growth layer 20 in the same manner as in the step (a) (second). Growth process).

Thereafter, a P-type electrode and an N-type electrode are formed respectively in the same manner as in a usual method for manufacturing a semiconductor laser.

In the first and second embodiments, Al _x Ga _1-x
Although the A1 composition of each layer composed of As and Al _y Ga _1-y As is described respectively, it goes without saying that they can be appropriately changed. However, in the case of A1 composition as in the above embodiment, the lower clad layer 21
With the light confinement effect of the first upper cladding layer 23, light can be efficiently emitted in the active layer 22. Further, it is possible to reverse all conductivity types.

(F) Effect In the first invention, a quantum effect is exerted by a protective layer interposed between the first upper clad layer and the second upper clad layer, and this protective layer has a band equal to or higher than that of the active layer. Since the gap can be provided, the electrical and optical properties of the semiconductor laser can be improved.

As described in detail above, according to the second aspect of the present invention, only the protective layer is selectively left in the etching process so that the first upper clad layer has a passivation effect, so that impurities are directly attached to the surface of the first upper clad layer. Instead, the impurities are evaporated by a relatively simple thermal cleaning, so that the laminated state of the second growth layer can be improved regardless of the A1 composition of the first upper cladding layer. That is, according to the present invention, the shape of the semiconductor laser having the above-described characteristics can be manufactured with good reproducibility and easily. As a result, the manufacturing yield can be improved.

[Brief description of drawings]

1 is a perspective view showing an embodiment of a semiconductor laser according to the first invention, FIG. 2 is an explanatory view showing a band structure of the semiconductor laser 1 shown in FIG. 1, and FIG. 3 is a view showing the second invention. It is a reference diagram for explaining one example of a manufacturing method of such a semiconductor laser. 10 ... Substrate, 20 ... First growth layer, 21 ... Lower clad layer, 22 ... Active layer, 23 ... First upper clad layer, 24 ...
Protective layer, 25 ... AlGaAs layer, 26 ... Current limiting layer, 30 ... Striped groove, 31 ... Tapered surface, 40 ... Second growth layer, 41 ...
… Second upper clad layer, 42 …… Cap layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masato Inougami 21 Saito Mizozaki-cho, Ukyo-ku, Kyoto City, Kyoto Prefecture Rome Co., Ltd. Address in Rome Co., Ltd. (72) Inventor, Hayami Fukada 21 in Saizo Mizozaki-cho, Ukyo-ku, Kyoto City, Kyoto Prefecture (56) Reference in JP-A-59-227179 (JP, A) J. Appl. Phys. Vol. 56 No. 2,15 Jul 1984 P.I. 463-467

Claims (2)

[Claims] 1. A lower clad layer made of AlGaAs of the same conductivity type as that of the substrate, which is sequentially laminated on the surface of a GaAs substrate of one conductivity type, an active layer made of Al _x Ga _1-x As, and the substrate. A first upper clad layer made of AlGaAs having a conductivity type opposite to that of
A protective layer made of GaAs having a band gap equal to or larger than that of the active layer due to a quantum effect and having a conductivity type opposite to that of the substrate, and AlGa having the same conductivity type as the substrate.
The As layer and a current limiting layer made of GaAs having the same conductivity type as the substrate constitute a first growth layer, and the first growth layer has a depth at which the surface of the protective layer is exposed and is on the substrate side. A second upper clad layer made of AlGaAs having a stripe groove in which a tapered surface narrowing toward the laser cavity wavelength is formed and is laminated on the first growth layer and has a conductivity type opposite to that of the substrate. And a cap layer for improving the ohmic contact, which constitutes the second growth layer. 2. An AlGaAs lower clad layer of the same conductivity type as that of the substrate, and Al on the surface of a substrate of one conductivity type GaAs.
_x Ga _1-x As active layer and Al of opposite conductivity type to the substrate
A first upper clad layer made of GaAs; a protective layer made of GaAs having a conductivity type opposite to that of the substrate and having a film thickness equal to or larger than that of the active layer due to a quantum effect and having a conductivity type opposite to that of the substrate; A first growth step of stacking a first growth layer composed of a conductive AlGaAs layer and a current limiting layer made of the same conductive GaAs as the substrate, and a solution having an etching rate of GaAs >> AlGaAs Selectively etching only the current limiting layer, then AlGaA
s >> A stripe groove having a taper surface with a depth that exposes the surface of the protective layer and narrows toward the substrate side by selectively etching only the AlGaAs layer with a solution having an etching rate of GaAs And a thermal cleaning step of evaporating impurities attached by the etching step by heating the substrate while applying an arsenic molecular beam to the first growth layer in which the stripe groove is formed, Stacking a second growth layer composed of a second upper cladding layer made of AlGaAs having a conductivity type opposite to that of the substrate and a cap layer for improving ohmic contact on the cleaned first growth layer; 2. A method for manufacturing a semiconductor laser, comprising the step of growing 2.