JPS6347277B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an embedded single-axis mode semiconductor laser suitable for use in optical fiber communications and the like.

Buried semiconductor lasers have excellent characteristics such as low threshold oscillation and single transverse mode oscillation, but because the oscillation wavelength changes significantly with temperature and the spectral half-width is large, they are not suitable for long-distance, high-capacity transmission systems. There were problems in using it. A known method to solve this problem is to use an internal periodic structure in the resonator of the semiconductor laser without depending on the cleavage plane, but if applied to an embedded semiconductor laser, it may impair its excellent characteristics or reduce its lifetime. Problems arose, such as affecting the growth process and complicating the growth process.

SUMMARY OF THE INVENTION An object of the present invention is to provide a single-axis mode semiconductor laser that has excellent characteristics as a buried semiconductor laser, has a long life, and has a simple growth process, in order to eliminate the above-mentioned drawbacks.

According to the present invention, a multilayer semiconductor wafer is formed by growing a semiconductor multilayer film including at least an active layer on a first conductivity type semiconductor substrate on which a periodic structure is formed over almost the entire surface, and at least two layers deeper than the active layer are formed on the multilayer semiconductor wafer. In a buried heterostructure semiconductor laser formed by etching a groove to form a mesa stripe and then growing it in a buried manner, the periodic structure has a period approximately equal to an integral multiple of 1/2 of the wavelength of the oscillated light in the active layer, The second conductivity type current blocking layer and the first conductivity type current blocking layer are sequentially laminated except for the upper surface of the mesa stripe including the active layer, and the second conductivity type buried layer is further laminated over the entire surface. A characteristic single-axis mode semiconductor laser is obtained.

In the present invention, in order to form a mesa stripe including an active layer for laser oscillation, a method is used in which a groove deeper than the active layer is etched in a multilayer semiconductor wafer. Therefore, the multilayer semiconductor including the active layer remains outside the grooves on both sides of the mesa stripe, which has the effect of increasing the breakdown voltage of the pnpn structure formed by the subsequent buried growth. Therefore, leakage current to areas other than the active layer can be extremely reduced. Therefore, the oscillation threshold current of the semiconductor laser can be reduced and high output operation can be achieved. At the same time, since the electrodes of the semiconductor laser can be electrodes on the entire surface, the device fabrication process can be greatly simplified. In addition, in the present invention, since the periodic structure necessary for single-axis mode oscillation is first formed on the semiconductor substrate, the yield of the process is high, and compared to the case where the periodic structure is formed after the active layer is grown, the active layer is No damage or deterioration. For the above reasons, the single-axis mode semiconductor laser of the present invention has excellent characteristics such as low threshold oscillation, long life, and simple growth process.

Next, the present invention will be explained using the drawings.

FIG. 1 is a cross-sectional view of one embodiment of the present invention, and FIG. 2 is a sub-sectional view thereof including a mesa stripe.
On the surface of the (100)-oriented n-InP substrate 100,
A periodic structure 101 with a period of about 2200 Å is formed over the entire surface in the 011> direction. This periodic structure 10
1 was created using a two-beam interference exposure method in which two He--Cd laser beams with a wavelength of 3250 Å intersect at an angle of approximately 43 degrees, and chemical etching. On the periodic structure 101, a guide layer 102 of n-InGaAsP with a bandgap wavelength of 1.3 μm and a thickness of 0.3 μm and an InGaAsP with an oscillation wavelength of 1.55 μm and a thickness of 0.1 μm are formed.
An active layer 103 and a P-InP cladding layer 104 having a thickness of 2 μm are grown in layers. <011> on the multilayer semiconductor wafer 110 consisting of these layers.
Two grooves 201 and 202 in the direction are etched to form a mesa stripe 300. On the etched multilayer semiconductor wafer 110, a seventh current blocking layer 105 of P-InP and a second current blocking layer 106 of n-InP are formed on only the upper surface of the mesa stripe 300 by the second crystal growth. In addition, a buried layer 107 of P-InP and a P-InP layer 107 with a forbidden band width of 1.2 μm
An InGaAsP ohmic layer 108 is deposited over the entire surface of the mesa stripe 300 and the second current blocking layer 106. In the second growth, in order to prevent the first and second current blocking layers 105 and 106 from growing on the mesa stripe 300, the soak temperature was maintained at 630°C for several hours, and then the temperature was increased to 0.7°C/100°C.
Two-phase solution-liquid phase growth was used, with growth starting at 620 °C when cooled at a rate of 1.5 min. In the above structure, when a current is injected from above the ohmic layer 108, the current flows through the first and second current blocking layers 105, 1
Due to the presence of 06, the light flows only into the mesa stripe 300 and can effectively cause laser oscillation. The active layer 103 and guide layer 102 in the mesa stripe 300 are buried vertically by the InP substrate 100 and cladding layer 104, and horizontally by the first current blocking layer 105, thereby cutting off higher-order modes. Stable single transverse mode oscillation is possible by parameter settings. A periodic structure 101 is formed at the boundary between the guide layer 102 and the InP substrate 100 and causes distributed feedback to the light wave in the optical waveguide composed of the active layer 103 and the guide layer 102, so that an axial mode determined by the period of the periodic structure 101 is generated. It is possible to stably oscillate only the

In the example, the active layer 300 in the mesa stripe 300 was less likely to be damaged due to contact with the carbon board for liquid phase growth during buried growth of the mesa stripe 300, and therefore the yield was significantly improved. According to this structure, the oscillation threshold current
A high-performance single-axis mode semiconductor laser with 50mA and 50% differential quantum efficiency was obtained with small variations in characteristics.

The embodiments of the present invention can be modified in various ways other than the examples. The InP substrate 100 may be of P type instead of n type. In this case, the conductivity types of the grown crystal layers are all opposite to those in the example. The oscillation wavelength is
A wavelength other than 1.55 μm may be used. Further, the guide layer 102 may have a thickness and a bandgap wavelength that may be changed as appropriate, and may also be an InP cladding layer as long as the periodic structure 101 is not lost. Further, the semiconductor substrate and the grown crystal layer may be other than those in the embodiment.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of one embodiment of the present invention, and FIG. 2 is a vertical cross-sectional view of 3. In the figure, 100...
InP substrate, 101... Periodic structure, 102... Guide layer, 103... Active layer, 104... Cladding layer, 105, 106... Current blocking layer, 107
... Embedded layer, 108 ... Omic layer, 110
...Multilayer film semiconductor wafer, 201, 202...
Groove, 300...Mesa stripe.

Claims (1)

[Claims] 1. Etching at least two grooves deeper than the active layer in a multilayer semiconductor wafer obtained by growing a semiconductor multilayer film including at least an active layer on a first conductivity type semiconductor substrate on which a periodic structure is formed over almost the entire surface. In a buried heterostructure semiconductor laser formed by forming a mesa stripe by forming a mesa stripe and then growing the buried heterostructure semiconductor laser, the periodic structure has a period approximately equal to an integral multiple of 1/2 of the wavelength of the oscillation light in the active layer, and A second conductivity type current blocking layer and a first conductivity type current blocking layer are sequentially laminated except for only the upper surface of the mesa stripe including the active layer, and a second conductivity type current blocking layer is sequentially laminated.
A single-axis mode semiconductor laser characterized in that a conductive buried layer is laminated over the entire surface.