JPS64835B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Industrial Application Field The present invention relates to an AlGaAs-based double heterojunction semiconductor laser that requires two MBE growth steps, and a method for manufacturing the same. (b) Prior Art A method for manufacturing a semiconductor laser having a structure that requires two MBE growth steps will be described below, and the problems thereof will be pointed out. First, after a first growth layer is laminated on the surface of the substrate in the first MBE growth process, the substrate is taken out from the MBE apparatus, and a stripe groove reaching the first upper cladding layer is formed in an etching process. As this etching process is carried out, impurities such as oxides are directly attached to the etched portions, so these impurities are evaporated by a predetermined method. After that, a second growth layer is laminated in a second MBE growth process. 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 are difficult to evaporate. This causes a problem in that the stacked state of the second grown layer deteriorates and 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, the second
Although the stacked state of the grown layers is improved, the problem arises that the light confinement efficiency is reduced. (c) Purpose The first invention aims to provide a semiconductor laser with improved electrical properties and optical properties. A second object of the present invention is to provide a method for manufacturing a semiconductor laser that can easily manufacture the shape of a semiconductor laser having the above-mentioned characteristics with good reproducibility and improve manufacturing yield. (d) Structure The semiconductor laser according to the first invention is characterized by a lower clad layer made of AlGaAs of the same conductivity type as the substrate, which is successively laminated on the surface of a GaAs substrate of one conductivity type, and an Al _an active layer made _of of the opposite conductivity type to the substrate
A first growth layer is composed of a protective layer made of GaAs and a current limiting layer made of Al _Y Ga _1-Y As having a conductivity type opposite to that of the protective layer, and has a depth at which the surface of the protective layer is exposed; A stripe groove having a tapered surface that becomes narrower toward the substrate side is formed in the first growth layer along the laser resonator wavelength, and a groove opposite to the substrate is formed on the top of the first growth layer in which the stripe groove is formed. The second growth layer consists of a second upper flat layer made of AlGaAs of the conductivity type and a cap layer made of high concentration GaAs of the same conductivity type as the second upper cladding layer. A feature of the method for manufacturing a semiconductor laser according to the second invention is that an AlGaAs lower cladding layer of the same conductivity type as the substrate is formed on the surface of a substrate made of GaAs of one conductivity type, and _{an Al} an active layer consisting of As;
a first upper cladding layer made of AlGaAs having a conductivity type opposite to that of the substrate; and a protective layer made of GaAs having a conductivity type opposite to that of the substrate and having a thickness set to have a band gap equal to or greater than that of the active layer due to quantum effects. and Al _Y of the opposite conductivity type to the protective layer.
The first layer consists of a current limiting layer made of Ga _1-Y As.
a first growth step of laminating growth layers, and selectively etching the current limiting layer with a solution that selectively etches only the current limiting layer to a depth where the surface of the protective layer is exposed; an etching step of forming striped grooves having a tapered surface that becomes narrower toward the substrate; and heating the substrate while applying an arsenic molecular beam to the first growth layer in which the striped grooves are formed. a thermal cleaning step to evaporate impurities deposited during the process; and a second upper cladding layer made of AlGaAs of a conductivity type opposite to that of the substrate and the second upper cladding layer on top of the thermally cleaned first growth layer. and a second growth step of laminating a second growth layer composed of a cap layer made of high-concentration GaAs of the same conductivity type. (E) First Embodiment of the 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 reflective surfaces. 10 is a substrate made of N-type GaAs, 21 is N-type Al _x Ga _1-x As (Al composition X = 0.55)
22 is Al _x Ga _1-x As
(Al composition X=0.12), and 23 is P
A first upper cladding layer made of type Al _x Ga _1-x As (Al composition X=0.55), 24 a protective layer made of P type GaAs, 25 a current limiting layer made of N type GaAs, 41
denotes the second upper cladding layer made of P type Al _Y Ga _1-Y As (Al composition Y = 0.55), 42 the cap layer made of P ⁺ type GaAs, 50 the P type electrode, and 51 the N electrode. There is. Note that the protective layer 24 is set to have a thickness that has a bandgap equal to or greater than that of the active layer 22 due to quantum effects. Specifically, the lower cladding layer 21 and the active layer 2
2, a first upper cladding layer 23, a protective layer 24, and a current limiting layer 25 constitute a first growth layer 20. This first growth layer 20 has stripe grooves 30 having a depth that exposes the surface of the protective layer 24 and a tapered surface 31 that becomes narrower toward the substrate 10 side.
is formed along the laser resonator wavelength of the semiconductor laser 1. and the second upper cladding layer 4
1 and the cap layer 42 constitute a second growth layer 40. This second growth layer 40 is laminated on top of the first growth layer 20 in a concave shape corresponding to the shape of the stripe groove 30. Therefore, the band structure at the center of the stripe groove 30 of the semiconductor laser 1 as described above is as shown in FIG. In Figure 2, A is the conduction band, B is the forbidden band,
C indicates a valence band, and it can be seen from the figure that the band gap of the protective layer 24 is wider than that of the active layer 22 due to quantum effects. Second invention FIG. 3 is a reference diagram for explaining a method of manufacturing a semiconductor laser according to the second invention, and the following description will be made with reference to the same diagram. (a) Board 10 installed in an MBE device (not shown)
is heated in a prescribed manner. The raw materials and impurities stored in the evaporation sources are evaporated in the form of molecular beams. The first growth layer 20 is laminated by monitoring the raw materials with a mass spectrometer (not shown) and controlling the temperature and shutter of the evaporation source with a computer (not shown) (first growth step).
It is assumed that the thickness of the protective layer 24 is set to about 30 to 40 Å. (b) The substrate 10 on which the first growth layer 20 is laminated
After taking it out from the MBE device, the board 10
Wrapping the back side of. Next, the current limiting layer 25 other than the portion where the stripe grooves are to be formed is covered with a photoresist 60. By immersing the substrate 10 using the photoresist 60 as a mask in a solution that selectively etches only the current limiting layer 25, the current limiting layer 25 is selectively etched to a depth where the surface of the protective layer 24 is exposed. A striped groove 30 having a tapered surface that becomes narrower toward the substrate is formed in the first growth layer 20 (etching step). The solution is 1,2-
Dihydroxybenzene-3,5-disulfonic
It is a 0.1M aqueous solution containing acid and 2Na salt as its main components, and is used under light irradiation from a halogen lamp, etc. However, the solution etches only the N-type current limiting layer 25. (c) The substrate 10 from which the photoresist 60 has been removed is organically cleaned. After that, the substrate 10 is replaced again.
Installed inside the MBE device. Here, by heating the substrate 10 while applying an arsenic molecular beam to the substrate 10, impurities such as oxides deposited during the etching process are evaporated (thermal cleaning process). However, the heating temperature and time are set so that the protective layer 24 made of GaAs does not evaporate. (d) In the state of step (c), the temperature of the substrate 10 is set to about 600°C, and the second growth layer 40 is grown in the same manner as in step (a).
is laminated on top of the first growth layer 20 (second growth step). Thereafter, a P-type electrode and an N-type electrode are respectively formed in the same manner as in a normal semiconductor laser manufacturing method. Therefore, the relationship between the substrate temperature and the GaAs evaporation rate is as shown in Table 1.

[Table] That is, the temperature and time of the thermal cleaning process are set based on Table 1. In addition, in the above first and second embodiments,
Al in each layer consisting of Al _X Ga _1-X As and Al _Y Ga _1-Y As
Although the respective compositions are described, it goes without saying that they can be changed as appropriate. However, Al as in the above example
In the case of the composition, light can be efficiently emitted within the active layer 22 due to the light confinement effect of the lower cladding layer 21 and the first upper cladding layer 23. Furthermore, it is also possible to reverse all conductivity types in the above embodiments. In this case, the current limiting layer 2
Since 5 is of P type, the etching method is different from the above embodiment. Therefore, the P-type current limiting layer 25
For selective etching, platinum as a cathode and substrate 1 as an anode are placed in the same solution as in the above example.
It is conceivable that the current limiting layer 25 of the substrate 10 may be selectively etched by immersing the current limiting layer 25 of the substrate 10 in the solution and causing an electrical reaction. (f) Effect The first invention is characterized in that a quantum effect is produced in the protective layer interposed between the first upper cladding layer and the second upper cladding layer, and the protective layer has a band gap equal to or larger than that of the active layer. This makes it possible to improve the electrical and optical properties of semiconductor lasers. As detailed above, the second invention allows impurities to be directly attached to the surface of the first upper cladding layer by selectively leaving only the protective layer in the etching process and giving the first upper cladding layer a passivation effect. Since the impurities are evaporated by relatively simple thermal cleaning without causing any growth, the laminated state of the second grown layer can be made good regardless of the Al composition of the first upper cladding layer. That is, according to the present invention, it is possible to easily manufacture the shape of a semiconductor laser having the characteristics as described above with good reproducibility. As a result, manufacturing yield can be improved.

[Brief explanation of drawings]

1 is a perspective view showing an embodiment of the semiconductor laser according to the first invention, FIG. 2 is an explanatory diagram showing the band structure of the semiconductor laser 1 shown in FIG. 1, and FIG. 3 is a perspective view showing an embodiment of the semiconductor laser 1 according to the second invention. FIG. 3 is a reference diagram for explaining an example of a method for manufacturing such a semiconductor laser. 10... Substrate, 20... First growth layer, 21...
lower cladding layer, 22... active layer, 23... first
Upper cladding layer, 24...protective layer, 25...current limiting layer, 30...stripe groove, 31...tapered surface, 40...second growth layer, 41...second upper cladding layer, 42...cap layer.

Claims (1)

[Scope of Claims] 1. A lower cladding layer made of AlGaAs of the same conductivity type as that of the substrate, and _an active layer made of _Al a first upper cladding layer made of AlGaAs of the opposite conductivity type to the substrate;
A first growth layer is composed of a protective layer made of GaAs and a current limiting layer made of Al _Y Ga _1-Y As having a conductivity type opposite to that of the protective layer, and has a depth at which the surface of the protective layer is exposed; A stripe groove having a tapered surface that becomes narrower toward the substrate side is formed in the first growth layer along the laser resonator wavelength, and a groove opposite to the substrate is formed on the top of the first growth layer in which the stripe groove is formed. 1. A semiconductor laser comprising a laminated second growth layer consisting of a second upper clad layer made of AlGaAs of the conductivity type and a cap layer made of high concentration GaAs of the same conductivity type as the second upper flat layer. 2. On the surface of one substrate made of GaAs of the conductivity type, an AlGaAs lower cladding layer of the same conductivity type as the substrate, an active layer made of Al _x Ga _1-X As, and an AlGaAs of the opposite conductivity type to the substrate. a first upper cladding layer; a protective layer made of GaAs of a conductivity type opposite to that of the substrate and set to a film thickness that has a band gap equal to or greater than that of the active layer due to quantum effects; A first growth step of laminating a first growth layer consisting of a current limiting layer made of Al _Y Ga _1-Y As, and a solution that selectively etches only the current limiting layer. an etching step of selectively etching to form a striped groove having a depth that exposes the surface of the protective layer and a tapered surface that becomes narrower toward the substrate; and a first groove in which the striped groove is formed. a thermal cleaning step in which impurities attached in the etching step are evaporated by heating the substrate while applying an arsenic molecular beam to the growth layer; and a step opposite to the substrate on the top of the thermally cleaned first growth layer. A second growth step of laminating a second growth layer consisting of a second upper cladding layer made of AlGaAs of the conductivity type and a cap layer made of high concentration GaAs of the same conductivity type as the second upper cladding layer. A method for manufacturing a semiconductor laser, characterized in that: