JP2850898B2 - Semiconductor laser and method of manufacturing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser and a method for manufacturing the same, and more particularly, to a semiconductor laser formed by using a low-pressure metal organic chemical vapor deposition (low-pressure MOCVD) method. The present invention relates to high power and narrow radiation beams and a method for manufacturing the semiconductor laser. 2. Description of the Related Art FIG. 5 shows, for example, Japanese Patent Application Laid-Open No. 60-192379.
FIG. 1 is a partially exploded perspective view showing a conventional semiconductor laser disclosed in Japanese Unexamined Patent Application Publication No. HEI 9-205, and is divided into a laser resonance end face and an inside of a laser for ease of explanation. In the figure, 1
Is a P-GaAs substrate, 2 is a P-Al _x Ga _1-x As cladding layer, 3 is P-Al
_y Ga _1-y As active layer, 4 is n-Al _x Ga _1-x As cladding layer, 5 is n
The -GaAs contact layer 6 is a ridge provided only near the resonator end face and extending in the resonator direction. 3a is an active layer grown on the ridge 6, and 3b is an active layer formed inside the laser chip. [0003] The semiconductor laser having the above-mentioned structure is formed on a P-GaAs substrate 1 on which a ridge 6 is formed, by a liquid phase epitaxy (LPE) method, by a P-Al _x Ga _{1 -x} As cladding layer 2. , P-
Al _y Ga _{1 -y} As active layer 3, n-Al _x Ga _{1 -x} As cladding layer 4, n-
GaAs contact layers 5 are sequentially grown. Here, in the liquid phase growth method, the growth rate on the ridge 6 is lower than the growth rate on the flat P-GaAs substrate 1. For this reason, the active layer 3a on the ridge at the laser end face is thinner than the active layer 3b inside the laser chip, which is a characteristic of this semiconductor laser. In a normal semiconductor laser, the thickness of the active layer is constant in the direction of the resonator, and in order to enable a narrow radiation beam and high-power operation, when the active layer is uniformly thinned, the threshold is reduced due to a decrease in gain. Increase or shorten the life. For this reason, in the semiconductor laser shown in FIG. 5, only the active layer at the laser end face is made thinner to enable a narrow radiation beam and a high output operation, and the inside of the laser chip which greatly affects the oscillation threshold value. The thickness of the active layer is slightly increased to control the increase in the oscillation threshold.
In addition, by making the active layer inside the laser chip slightly thicker as described above, the life can be extended. FIG. 6 is an exploded perspective view showing another conventional example disclosed in Japanese Patent Application Laid-Open No. Sho 60-192379, and the same parts as those in FIG. 5 are indicated by using the same symbols. In the figure, reference numeral 7 denotes an n-GaAs current block layer, and 8 denotes a groove penetrating the n-GaAs current block layer 7. The P-Al _x Ga _1-x As clad layer 2, the P-Al _y Ga _1-y As active layer 3, the n-Al _x Ga _1-x As clad layer 4, and the n-GaAs contact layer 5 Using the phase growth method
It is sequentially grown on a P-GaAs substrate 1. In the semiconductor laser thus configured, the thickness of the active layer is reduced only at the laser end face, similarly to the semiconductor laser shown in FIG.
High output operation, low oscillation threshold, and long life are possible. Further, by providing the groove 8, a so-called loss guide transverse mode control mechanism is configured so that stable transverse mode oscillation can be performed. As described above, in the conventional semiconductor laser, liquid phase growth is performed to reduce the thickness of the active layer only at the end face of the laser and keep the thickness of the active layer inside the laser at an appropriate level. It is formed using the fact that the growth rate on the ridge in the method is lower than the growth rate on the flat portion. However, when each layer is grown by a reduced pressure metal organic chemical vapor deposition (MOCVD) method which can use a large-area wafer and has excellent film thickness control accuracy,
Since the growth rate on the ridge and the growth rate on the flat portion are the same, the active layer cannot be thinned only at the laser end face portion, and accordingly, there is a problem that a semiconductor laser having such a configuration cannot be obtained. doing. The present invention has been made in order to solve such a problem, and even if it is manufactured using a reduced-pressure metal organic chemical vapor deposition method, only the thickness of the active layer near the laser end face is properly adjusted. An object of the present invention is to obtain a semiconductor laser having a narrow radiation beam, a high output operation, a low threshold value, and a long life by setting the thickness. [0010] A semiconductor laser according to the present invention comprises a compound semiconductor substrate having a uniformly flat main surface, and a stripe portion which is narrower than the width of the substrate along a laser light guiding direction. Is disposed on the substrate so as to have, and is thinner in the vicinity of the laser light emitting end face than the thickness inside the substrate surface and
Both in the width direction of the substrate inside the substrate surface and near the emission end face
An active layer uniformly separated from the substrate surface along the waveguide, a waveguide formed by laminating a first clad layer and a second clad layer via the active layer, and a waveguide disposed on the substrate along the waveguide. And a provided current blocking layer. [0011] semiconductor laser manufacturing method of the reduction compounds dielectric film on a substrate facing each other via a stripe portion along the waveguide direction of the laser beam on the semiconductor substrate according to the present invention
A step of covering the substrate so that the width of the substrate surface in a direction intersecting the waveguide direction with the dielectric film remains wide near the emitting end face of the laser light. Forming a waveguide in which a first cladding layer, an active layer, and a second cladding layer are sequentially laminated on a substrate by a reduced pressure metal organic chemical vapor deposition method using the body film as a selective growth mask ;
Is included. In the method of manufacturing a semiconductor laser, Al _x Ga ₁ is deposited on a GaAs substrate partially formed with a SiO ₂ film and a Si ₃ N ₄ film by a reduced-pressure metalorganic vapor phase epitaxy method. _After growing the _-x As layer and the GaAs layer, the Al _x Ga _1-x As
Layers and GaAs layers grow, but not on SiO ₂ and Si ₃ N ₄ films. In the reduced-pressure metalorganic vapor phase epitaxy, trimethylgallium (TMG), trimethylaluminum (TMA), and arsine (AsH ₃ ) supplied in a gaseous state are used.
Decomposes near the substrate, which causes a chemical reaction to grow epitaxially on the substrate. TMG, TM decomposed on the SiO ₂ film or Si ₃ N ₄ film on the substrate
A, AsH _3, without Epitakyasharu grow on SiO ₂ film or the Si ₃ N ₄ film, moved to the portion GaAs by diffusing SiO ₂ film or Si ₃ N ₄ Makujo is exposed, There, epitaxy grows. For this purpose, SiO ₂ film or Si ₃ N
The amount of Ga, Al , As contributing to the growth increases on the GaAs substrate slightly away from the SiO ₂ film or the Si ₃ N ₄ film than on the GaAs substrate sufficiently far from the ₄ film. The growth rate becomes faster. By utilizing the difference in the growth rates, in this semiconductor laser, the thickness of the active layer can be made thin near the end face and thick inside the laser chip. Embodiment 1 Hereinafter, Embodiment 1 of the present invention will be described with reference to the drawings. FIG. 1 is an exploded perspective view showing a semiconductor laser according to the present invention, and the same parts as those in FIGS. 5 and 6 are indicated by using the same symbols. In FIG. 1, reference numeral 9 denotes an SiO ₂ film provided only on a part of the flat P-GaAs substrate 1. In the semiconductor laser thus constructed, first, a P-Al _x Ga _{1 -x} As cladding layer 2 is formed on the surface of a P-GaAs substrate 1 shown in FIG. , P-Al _y Ga
_1-y As active layer 3, n-Al _x Ga _1-x As cladding layer 4, n-GaAs
The contact layers 5 are sequentially grown. Here, as shown in FIG. 2, two portions of the SiO ₂ film 9 are formed inside the laser chip so that the stripe portion 1 having a constant width is formed therebetween.
0 is provided. Therefore, P-Ga
This means that the surface of the As substrate 1 is exposed. Next, the P-Al _x Ga _{1 -x} As cladding layer 2, P-
Al _y Ga _1-y As active layer 3, n-Al _x Ga _1-x As cladding layer 4, n-
When the GaAs contact layer 5 is sequentially grown, it does not grow on the SiO ₂ film 9 but grows only on the portion where the P-GaAs substrate 1 is exposed. Also, the TM decomposed on the SiO ₂ film 9
Since G and TMA are not consumed on the SiO ₂ film 9, the SiO ₂
Diffusion on the film 9 reaches a portion where the SiO ₂ film 9 such as the stripe portion 10 is cut. Therefore, more Ga and Al are supplied to the stripe portion 10 than in the vicinity of the end face of the laser chip. Accordingly, the thickness of each layer of the stripe portion 10 inside the laser chip is reduced. The thickness of each layer is larger than the thickness of each layer in the vicinity, and a semiconductor laser having the structure shown in FIG. 1 is obtained. And
In the semiconductor laser configured as described above, the active layer becomes thinner only at the end face of the laser chip.
High output operation, low threshold value, and long life can be obtained. This will be described in detail below. The length of the laser resonator is 250 μm, and the SiO ₂ film 9 is formed in a chip 15 μm away from both end faces. The width of the stripe portion 10 is 10 μm. The oscillation threshold current of the laser is substantially determined by the thickness of the active layer 3b formed on the stripe portion 10. When the thickness of the active layer is about 0.1 μm, the oscillation threshold current becomes minimum. On the other hand, when the thickness of the active layer near the end face of the laser resonator is reduced, the amount of light leaking from the active layer 3a to the cladding layers 2 and 4 increases, and the light emission spot at the end face increases. As a result, light seeping from the active layer 3a to the cladding layers 2 and 4 increases, and the light density at the laser end face decreases,
End face destruction is less likely to occur, and high-output operation is possible. Further, when the light emitting spot on the end face becomes large, the radiation beam becomes narrow. For example, when the thickness of the active layer at the end face is 0.1 μm, the full width at half maximum in the direction perpendicular to the junction of the radiation beam is about 40 °, but when it is 0.03 μm, it becomes as narrow as about 16 °. Therefore, if the thickness of the active layer 3b inside the resonator is set to 0.1 μm and the thickness of the active layer 3a near the resonator is set to 0.03 μm,
A semiconductor laser having a low threshold value, a narrow radiation beam, and a high output can be obtained. Embodiment 2 FIG. 3 is a perspective view showing another embodiment of a semiconductor laser according to the present invention, particularly showing a case where the present invention is applied to a semiconductor laser having a transverse mode control mechanism. Less than,
The manufacturing method will be described with reference to the process charts shown in FIGS. First, as shown in FIG. 4A, an n-GaAs current block layer 7 is formed on a P-GaAs substrate 1, and
An SiO ₂ film 9 is formed on the P-GaAs substrate 1 in a portion inside the laser resonator. Next, as shown in FIG. 4B, after applying a resist 11, a portion of the resist 1 where a stripe portion 10 shown in FIG.
Remove only one. Next, as shown in FIG. 4 (c), dry etching using CF ₄
The SiO ₂ film 9 is removed. Next, a wet etching process is performed using the resist 11 as a mask.
The groove 8 shown in (d) is formed. Next, after the resist 11 is removed, P-Al _x Ga is deposited on the grooved substrate by using reduced pressure metal organic chemical vapor deposition.
_1-x As cladding layer 2, P-Al _y Ga _1-y As active layer 3, n-Al _x Ga
By sequentially forming the _1-x As cladding layer 4 and the n-GaAs contact layer 5, a semiconductor laser having the structure shown in FIG. 3 is obtained. That is, in the semiconductor laser formed in this manner, the active layer is bent to reflect the shape of the groove 8. Here, since the left and right sides of the active layers 3a and 3b are surrounded by the cladding layer 2 having a smaller refractive index than the active layer, an optical waveguide mechanism is formed, and the transverse mode can be controlled. Further, in this semiconductor laser, SiO ₂
Under the influence of the film 9, the active layer 3b at the end face of the resonator becomes thinner than the active layer 3b inside the resonator, so that a narrow radiation beam, a high output operation, a low threshold value and a long life can be achieved. Become. The semiconductor laser according to the present invention is partially
When an Al _x Ga _1-x As layer and a GaAs layer are grown on a GaAs substrate on which a SiO ₂ film and a Si ₃ N ₄ film are formed by reduced pressure metalorganic chemical vapor deposition, Al _x Ga _{1 -x} As layer and GaAs
Layers grow but do not grow on SiO ₂ and Si ₃ N ₄ films. In the reduced-pressure metalorganic vapor phase epitaxy, trimethylgallium (TMG), trimethylaluminum (TMA), and arsine (AsH ₃ ) supplied in a gaseous state are used.
Decomposes near the substrate, which causes a chemical reaction to grow epitaxially on the substrate. TMG, TM decomposed on the SiO ₂ film or Si ₃ N ₄ film on the substrate
A, AsH _3, without Epitakyasharu grow on SiO ₂ film or the Si ₃ N ₄ film, moved to the portion GaAs by diffusing SiO ₂ film or Si ₃ N ₄ Makujo is exposed, There, epitaxy grows. For this reason, the SiO ₂ film or the Si ₃ N ₄ film is farther than the SiO ₂ film or the Si ₃ N ₄ film on the GaAs substrate.
On a GaAs substrate slightly away from the film,
The amount of a, Al, As increases, and the growth rate increases accordingly. By utilizing this difference in growth rate, the thickness of the active layer can be reduced near the end face and increased within the laser chip. As described above, the semiconductor laser according to the present invention is formed on a compound semiconductor substrate having a uniformly flat main surface, in the vicinity of the emission end face of the laser beam due to the thickness inside the substrate surface. Thin and inside the substrate surface and near the emission end face
Both the active layer is uniformly separated from the substrate surface along the substrate width direction, and the first clad layer and the second clad layer are interposed via this active layer.
Are disposed so as to have a stripe portion that is narrower than the width of the substrate along the waveguide direction of the laser light, and a current blocking layer is formed on the substrate along the waveguide. Is provided, the lateral mode can be controlled, and there is an effect that a semiconductor laser having a narrow radiation beam, a high output operation, a low threshold value, and a long life can be obtained. [0031] semiconductor laser manufacturing method of the reduction compounds dielectric film on a substrate facing each other via a stripe portion along the waveguide direction of the laser beam on the semiconductor substrate according to the present invention
Formed through a current blocking layer formed to cover the dielectric film in a wide remains so over the substrate width direction of the substrate surface which intersects the guiding direction at the exit end face neighborhood of the laser beam, the dielectric the film as a selective growth mask vacuum MOCVD, the first cladding layer on a substrate, the active layer and the second clad layer was made to form formed sequentially stacked waveguide, current blocking It is possible to form an active layer that is thinner near the emission end face of the laser light than the inside of the laser, and can control the transverse mode accordingly, and can achieve a narrow radiation beam, high output operation, low threshold and long life. There is an effect that a semiconductor laser can be easily obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially exploded perspective view of a semiconductor laser according to an embodiment of the present invention. FIG. 2 is a perspective view showing a substrate portion of the semiconductor laser shown in FIG. FIG. 3 is a partially exploded perspective view showing another embodiment of the semiconductor laser according to the present invention. FIG. 4 is a process chart showing a manufacturing process of the semiconductor laser shown in FIG. 3; FIG. 5 is a perspective view showing a conventional semiconductor laser. FIG. 6 is a perspective view showing a conventional semiconductor laser. [Description of Signs] 1 P-GaAs substrate, 2 P-Al _x Ga _1-x As cladding layer,
3 P-Al _y Ga _{1 -y} As active layer, 4 n-Al _x Ga _{1 -x} As cladding layer, 5 n-GaAs contact layer, 6 ridge,
7 n-GaAs current block layer, 8 groove, 9
SiO ₂ film, 10 stripes, 11 resist

Claims (1)

(57) [Claims] A compound semiconductor substrate having a uniformly flat main surface, disposed on the substrate so as to have a stripe portion that is narrower than the width of the substrate along the waveguide direction of the laser light, and is disposed inside the substrate surface of the substrate. Thinner in the vicinity of the emission end face of the laser light than in the thickness ,
Both the active layer is uniformly separated from the substrate surface along the substrate width direction, and the first clad layer and the second clad layer are interposed via this active layer.
A semiconductor laser, comprising: a waveguide formed by laminating the cladding layers described above; and a current blocking layer disposed on the substrate along the waveguide. 2. Dielectric films opposed to each other via a stripe portion along the waveguide direction of laser light are formed on a compound semiconductor substrate.
Forming a current blocking layer formed thereon, and covering the substrate so that the width of the substrate surface in the direction intersecting with the waveguide direction in the dielectric film remains wide near the emitting end face of the laser light; Forming a waveguide in which a first clad layer, an active layer, and a second clad layer are sequentially stacked on the substrate by a reduced pressure metal organic chemical vapor deposition method using the dielectric film as a selective growth mask ; A method for manufacturing a semiconductor laser comprising: