JPS6251519B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a distributed reflection semiconductor laser that has at least one distributed reflector and oscillates in a single-axis mode.

The conventionally known distributed reflection semiconductor laser is
An optical guide layer, an active layer, a cladding layer, etc. are sequentially grown on a semiconductor substrate, and then the active layer in the distributed reflection section is removed by etching, and a layer of 1/1 of the optical wavelength in the active layer is formed on the exposed boundary surface of the waveguide. It formed a periodic structure with an integral multiple of 2. Since this type of semiconductor laser forms a periodic structure after crystal growth is completed, it has the drawback of low yields due to difficulties in etching and other reasons. Furthermore, there is no known method for applying a buried structure aimed at high efficiency to this type of semiconductor laser, and it has been difficult to reach the level of continuous oscillation at room temperature.

The present invention is a distributed reflection type semiconductor laser in which a periodic structure is formed on a semiconductor substrate in advance, and then a light guide layer, an active layer, a cladding layer, etc. are grown as crystals, and furthermore, there is no active layer in the distributed reflection part. Furthermore, the present invention provides a distributed reflection type semiconductor laser that can easily realize a buried structure.

According to the present invention, the concave groove has a lower part substantially orthogonal to the laser oscillation axis and another higher part, and a periodic structure having an integral multiple of 1/2 of the optical wavelength inside the crystal is formed in this higher part. A semiconductor substrate of a first conductivity type, an optical guide layer of a first conductivity type formed on the entire surface of this semiconductor substrate, and an active layer formed only on a portion of the guide layer located above the lower portion. and a first of a second conductivity type.
A distributed reflection semiconductor laser is obtained that includes a cladding layer and a second cladding layer of a second conductivity type grown on both the portion of the light guide layer located above the ridge and the first cladding layer. It will be done.

Note that the light guide layer must propagate the light amplified in the photoactive layer with extremely low loss, so the tourniquet width of the light guide layer is made larger than the tourniquet width of the photoactive layer to reduce light absorption. It is necessary to take measures to prevent this from happening.

Next, the distributed reflection type semiconductor laser of the present invention will be explained using the drawings.

FIG. 1 is a longitudinal sectional view of a first embodiment of the invention. FIG. 2 is a cross-sectional view of the low part 100 of the first embodiment, and FIG. 3 is a cross-sectional view of the high part 200 of the first embodiment. The n-InP substrate 1 consists of a lower part 100 and a higher part 200 formed by etching. The surface of the high part 200 is etched using two-beam interferometry and chemical etching to adjust the internal light wavelength of the crystal.
A diffraction grating 13 with a period corresponding to 1/2 is formed. A light guide layer 2 of _{n-In 0.82 Ga 0.18 As 0.40 P 0.60 with a bandgap wavelength of 1.15} μm is grown on the lower portion 100 and the upper portion ₂₀₀ . On the optical guide layer 2 on the upper side of the lower part 100, _{In 0.72} Ga _{0.28 As 0.61} P _0.39 with a bandgap wavelength ( _oscillation wavelength) of 1.30 μm _is formed.
An active layer 3 of p-InP and a first cladding layer 4 of p-InP are grown. The optical guide layer 2 above the high part 200 and the first cladding layer 4 above the low part 200 are
-The fourth cladding layer 7 of InP and the bandgap wavelength is 1.30
_μm n-In _{0.72 Ga 0.28 As 0.61} P _0.39 cap _{layer 8}
is growing. Zinc is diffused from the cap layer 8 to the fourth clad layer 7 on the upper side of the lower part 100, and the resistance between the first electrode 9 formed on the cap layer 8 and the fourth clad layer 7 is lower than that of the lower part 100. Only the area above 100 is low. In the lower part 100, the light guide layer 2, the active layer 3, the first
A crystal layer consisting of the ground layer 4 is divided into three parts by two grooves, and a mesa-shaped stripe 21 is formed in the center. These two grooves are filled with a second cladding layer 5 of p-InP and a third cladding layer 6 of n-InP. It does not grow on the first cladding layer 4. This can be realized by appropriately determining the conditions during crystal growth. on the other hand,
In the high part 200, the light guide layer 2 is in the low part 100.
It is divided into three parts by the same two grooves as the part. These two grooves, like the lower portion 100, are filled with the second cladding layer 5 and the third cladding layer 6. The second electrode 10 is formed under the substrate 1. The operation of the present invention will be explained based on the above structure. In the lower part 100, light propagates in the active layer 3 and the light guide layer 2, and in the higher part 200, light propagates in the light guide layer 2. The active layer 3 in the lower portion 100 has an amplifying effect on light having a wavelength of around 1.3 μm. Further, the open surface 11 reflects the light propagating within the active layer 3 and the light guide layer 2 in the opposite direction, and the diffraction grating 13 reflects the light propagating within the light guide layer 2 in the reverse direction by Bragg diffraction. Due to these effects, one embodiment of the present invention performs laser oscillation at a wavelength of 1.3 μm. FIG. 4 is a diagram showing a manufacturing procedure of an embodiment of the present invention. First, as shown in Section 4a, a concave groove is formed on the InP substrate 1 in a direction perpendicular to the semiconductor laser oscillation axis by chemical etching using photoresist as a mask, and then the high parts 200 on both sides of the groove are formed. The diffraction grating 13 is formed using a He--Cd laser two-beam interference exposure method and chemical etching. Next, a light guide layer 2, an active layer 3, and a first cladding layer 4 are grown on the entire surface of the substrate 1 by epitaxial growth. (Figure 4a). At this time,
The first cladding layer 4 is grown thickly so that the surface approaches flatness. Next, chemical etching is performed until the light guide layer 2 is exposed at the high portion 200. Further, following this etching, two grooves are etched until they reach the height of the substrate in the lower part 100 in order to form a mesa-like stripe 21 in the direction of the oscillation axis (FIG. 4d). Then,
Perform the second epitaxial growth,
The third and fourth cladding layers 5, 6, 7 and the cap layer 8 are grown (FIG. 4e). Next, zinc is diffused only in the part directly above the active layer 3 in the mesa-shaped stripe 21 so as to reach the fourth cladding layer 7, and then a first electrode 9 is spread over the entire front surface and a second electrode is spread over the entire back surface. form 10. A distributed reflection semiconductor laser can be obtained by opening the wafer, which has been processed up to this point, so as to be perpendicular to the mesa-shaped stripes 21 at the lower part 100 and cutting it at the higher part 200. As can be seen from the above explanation, in this distributed reflection semiconductor laser,
The active layer 3 and the optical guide layer 2 have a buried structure in the low part 100, and only the optical guide layer 2 has a buried structure in the high part 100.
A diffraction grating 13 serving as a distributed reflector is formed at the interface of the light guide layer 2 .

This embodiment has the advantage that a distributed reflection semiconductor laser with a buried structure can be obtained with two epitaxial growth steps.Moreover, the diffraction grating 13 of the distributed reflector can be formed before the start of epitaxial growth. It has the advantage of high yield.

Next, a modification of this embodiment will be described. active layer 3
The prohibited width is not limited to 1.3μm, but is 1.5μm.
etc. In addition, when the forbidden band width is set to 1.5 μm, in order to facilitate crystal growth on the active layer 3, a quaternary mixed crystal having a forbidden band width of about 1.3 μm may be further laminated. In addition to the crystal structure of this example,
A structure in which a layer of InP or quaternary mixed crystal is inserted as appropriate,
A chemical etching stop layer may also be provided. The conductivity type of the substrate 1 may be P type.
In that case, it is necessary to make the conductivity type of the other growth layer opposite to that in this embodiment. Furthermore, the substrate 1 and the quaternary mixed crystal are InP and
It may be other than In _1-x Ga _x As _y P _1-y (ox, y1). In this embodiment, the open surface 11 is used as one of the reflectors, but a distributed reflector of a diffraction grating may be used instead. In the case of 3, it is desirable that the length of the diffraction grating of the light guide layer 2 on the light extraction side is shorter than that of the other side. In this example, two grooves were formed to form the striped mesa 21, but after the striped mesa 21 was isolated on the substrate 1, the second growth was performed. Good too. Or striped mesa 2
1 may be omitted and a planar stripe structure may be used.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view of one embodiment of the present invention;
FIG. 3 is a cross-sectional view of the lower portion 100 and the higher portion 200, respectively. FIG. 4 is a diagram showing the manufacturing procedure of one example, a to c are longitudinal cross-sectional views, and d to e
is a cross-sectional view. In the figure, 1...substrate, 2... light guide layer,
3...active layer, 4,5,6,7...clad layer,
13... Diffraction grating, 21... Striped mesa,
100...low part, 200...high part.

Claims (1)

[Claims] 1 It has a lower part of the concave groove that is almost perpendicular to the laser oscillation axis and a higher part, and the upper part has the wavelength of light inside the crystal.
A semiconductor substrate of a first conductivity type in which a periodic structure having an integral multiple of 1/2 is formed, an optical guide layer of a first conductivity type formed on the entire surface of the semiconductor substrate, and a light guide layer of a first conductivity type located above the lower part. an active layer and a first cladding layer of a second conductivity type formed only on a portion of the light guide layer that is located above the high portion; and a second cladding layer of a second conductivity type grown thereon.