JPS6342876B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a single-axis mode oscillation semiconductor laser which is an embedded type and oscillates in a single-axis mode.

Although buried semiconductor lasers have excellent characteristics such as low threshold oscillation, they have the disadvantage that the oscillation axis mode is not stable and the oscillation wavelength varies greatly with temperature. In order to solve this drawback, attempts are being made to convert the buried semiconductor laser into a distributed feedback laser. Conventional methods include forming a periodic structure (unevenness) on the upper or lower side of the active layer with a period that is an integral multiple of 1/2 of the oscillation light wavelength in the active layer, or forming a periodic structure (unevenness) on the outside of the side surface of the active layer. Methods for forming structures, etc. were implemented. The former method has problems such as difficulty in growing the semiconductor layer and difficulty in extending the life of the obtained semiconductor laser. Although the latter method is preferable in terms of longevity, it is difficult for various reasons to create an appropriate periodic structure on the outside of the side surfaces of the active layer, and it also has problems such as difficulty in continuous oscillation at room temperature.

SUMMARY OF THE INVENTION In order to solve these problems, an object of the present invention is to provide an extremely highly efficient buried type single-axis mode oscillation semiconductor laser in which single-axis mode oscillation can be realized without deteriorating the characteristics.

According to the present invention, in a semiconductor wafer in which a semiconductor layer including at least an active layer is grown on a semiconductor substrate of a first conductivity type, only the upper surface of a mesa stripe formed by forming two etching grooves deeper than the active layer is removed. a second conductivity type current blocking layer laminated in sequence;
In a buried semiconductor laser including a first conductivity type current blocking layer and a second conductivity type buried layer laminated over the entire surface of the mesa stripe and the first conductivity type current blocking layer, a period is formed on the side surface of the mesa stripe. A single-axis mode oscillation semiconductor laser is obtained, which is characterized by forming a periodic structure of concavities and convexities having an integral multiple of 1/2 of the wavelength of oscillation light in the active layer.

In the single-axis mode oscillation semiconductor laser of the present invention, firstly, the semiconductor wafer including the active layer has two
Since it uses a buried semiconductor laser structure in which a mesa stripe formed by a book groove is embedded, it has the advantage that highly efficient oscillation is possible even when it is a distributed feedback type. Second, since a periodic structure of concavities and convexities is formed on the side boundaries of the mesa stripes,
It has the advantage that it causes very little damage to the active layer of the semiconductor laser, is advantageous in extending its life, and does not make it difficult to re-grow the semiconductor on the mesa stripe. In addition, since the periodic structure is located at the side boundary of the active layer, where the oscillation optical electric field distribution is relatively large, the effect is large, and the period of the periodic structure can be made quadratic or higher, making it very easy to fabricate. There is. Regarding a buried semiconductor laser in which a mesa stripe formed by forming two grooves in a semiconductor wafer including an active layer is buried, see the patent application specification of patent application No. 166666/1983 by Kitamura et al. Please refer to "Semiconductor Laser".

Next, embodiments of the present invention will be described using the drawings.

FIG. 1 is a perspective view of a single-axis mode oscillation semiconductor laser 1 according to an embodiment of the present invention. This is a semiconductor wafer 1 in which an n-InP buffer layer 102, an InGaAsP active layer 103 with an oscillation wavelength of 1.5 μm, and a p-InP cladding layer 104 are epitaxially grown on an n-InP wafer 101 with a (100) plane orientation. ,＜011
> Parallel to the direction with a width of 5 μm and a depth of 3 μm.
The grooves 151 and 152 are etched to leave the central mesa stripe 150 for light emission recombination and to form an uneven periodic structure with a period of 0.95 μm on the sides of the mesa stripe 250, and the resulting etched semiconductor A p-InP current blocking layer 105 and an n-InP current blocking layer 10 are formed on the wafer 2.
6 was epitaxially grown in sequence except for the upper surface of the mesa stripe 150, and then a p-InP buried layer 107 and a p-InGaAsP layer 108 were grown over the entire surface.

FIGS. 2, 3, and 4 sequentially show the manufacturing process of a single-axis mode oscillation semiconductor laser according to an embodiment of the present invention. FIG. 2 is a perspective view of the semiconductor wafer 1, FIG. 3 is a plan view showing the patterns of the first and second protective films 201 and 202 formed on the semiconductor wafer 1, and FIG. 4 is a diagram showing the pattern after etching is completed. FIG. 2 is a perspective view of an etched semiconductor wafer 2. FIG. Third
The first protective film 201 in the figure is 4416 of He-Cd laser.
This is a photoresist film in the form of periodic stripes along the <011> direction, which is produced by a two-beam interference exposure method in which oscillated light of 3.5 Å interferes with each other at an angle of about 53 degrees. its cycle
0.95 μm corresponds to 2.5 times the oscillation light wavelength of the active layer in the mesa stripe, and functions as a fifth-order diffraction grating for the oscillation light. The second protective film 202 in FIG. 3 is formed by forming and baking the first protective film 201, applying photoresist, and exposing the grooves in the <011> direction using a photomask.
It is a photoresist film with a groove width of approximately 15 μm. FIG. 4 shows the first and second protective films 201 and 202 in FIG.
FIG. 2 is a perspective view of an etched semiconductor wafer 2 after etching the semiconductor wafer 1 using the etching method. In etching, first,
The rectangular opening where the second protective films 201 and 202 are not attached is etched, but as the etching progresses, most of the area under the thin first protective film 201 is removed by side etching, and the second protective film 201 is mainly etched.
It is etched into a shape determined by the shape of the protective film 202. Therefore, the shape of the mesa stripe 150 of the etched semiconductor wafer 2 has a concavo-convex periodic structure having the same period as that of the first protective film 201 on its side surface. Thereafter, the etched semiconductor wafer 2 is embedded and grown to obtain the single-axis mode oscillation semiconductor laser 10 shown in FIG.

The single-axis mode oscillation semiconductor laser of the present invention has the advantage that no extra epitaxial growth is required to form a periodic structure for causing single-axis mode oscillation. Also,
Since the periodic structure is formed directly on the side boundary of the mesa stripe 150, the effect of distributed feedback is large.
Therefore, the periodic structure does not need to be of primary order, and a period of secondary or higher order is sufficient, so there is an advantage that manufacturing is very easy. Furthermore, the periodic structure is the active layer 1
Since it is not on the upper or lower surface of 03, there are advantages such as there is no need to impair the service life. Note that the periodic structure may be provided only on one side.

The embodiments of the present invention may have various forms in addition to the embodiments described above. InP wafer 101
may be of p-type. In this case, it is necessary for the grown semiconductor layer to have a conductivity type completely opposite to that of the embodiment. In addition, the crystal structure of this example is InP
And it may be something other than InGaAsP. Also,
It goes without saying that the oscillation wavelength is not limited to 1.5 μm and may be any other wavelength.

[Brief explanation of the drawing]

Figures 1, 2, 3 and 4 are respectively
FIG. 1 is a perspective view of an embodiment of the present invention, a perspective view of a semiconductor wafer, a view showing patterns of first and second etching protection films, and a perspective view of an etched semiconductor wafer. In the figure, 1... semiconductor wafer, 2... etched semiconductor wafer, 101... n-
InP wafer, 102... Buffer layer, 103...
...active layer, 104...clad layer, 105...p
-InP current blocking layer, 106...n-InP current blocking layer, 107...p-InP buried layer, 10
8... Ohmic layer, 150... Mesa stripe, 151, 152... Groove.

Claims (1)

[Claims] 1. A semiconductor wafer in which a semiconductor layer including at least an active layer is grown on a semiconductor substrate of a first conductivity type, and the mesa stripes formed by forming two etched grooves deeper than the active layer are sequentially laminated except for the upper surface. a second conductivity type current blocking layer, a first conductivity type current blocking layer, and a second conductivity type buried layer laminated over the entire surface of the mesa light stripe and the first conductivity type current blocking layer. 1. A single-axis mode oscillation semiconductor laser, characterized in that a concavo-convex periodic structure whose period is an integral multiple of 1/2 of the wavelength of oscillation light in the active layer is formed on the side surface of the mesa stripe.