Coherent light generators – Particular active media – Semiconductor
Patent
1989-11-21
1992-05-19
Epps, Georgia
Coherent light generators
Particular active media
Semiconductor
372 45, 372 48, 357 16, 357 17, H01S 319
Patent
active
051154439
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a semiconductor laser apparatus and its manufacturing method and, more particularly, to a high efficient semiconductor laser and its simplified manufacturing method.
PRIOR ART
FIG. 6(a) is a schematic constructional diagram of a conventional semiconductor laser. FIG. 6(b) is a graph showing a distribution of refractive indices of such a laser.
In the diagram, a buffer layer 2 of n-GaAs having a thickness of about 0.5 .mu.m is formed on an n-GaAs substrate 1. Further, a clad layer 3 of n-Al.sub.x Ga.sub.y As (x=0.3, y=0.7) having a thickness of 1.5 .mu.m is formed on the buffer layer 2.
Next, a non-doped GaAs active layer 4 having a thickness of 0.1 .mu.m and a clad layer 5 of p-Al.sub.x Ga.sub.y As (x=0.3, y=0.7) having a thickness of 1.5 .mu.m are formed. Further, a p-GaAs contact layer 6 having a thickness of 0.5 .mu.m is formed. Finally, an Au-Ge electrode 7 and an Au-Sn electrode 8 are formed.
When a voltage is applied to the semiconductor laser having the above construction, a current applied from the electrode 7 spreads until it reaches the electrode 8. For instance, assuming that a thickness v of the electrode 7 is about 5 .mu.m, the current spreads as shown by arrows 9 and a current which is necessary for oscillation also increases (about 150 to 200 mA).
Further, in the conventional example, as shown in FIG. 6(b), since a refractive index n of the active layer is set to about 3.65 and a refractive index n of the clad layer is set to about 3.4, although the light can be shut up in the vertical direction by the clad layers 2 and 5, the light cannot be shut up in the lateral direction. Therefore, there is a drawback such that the extent of the light increases, causing a deterioration of the differential quantum effect or the like.
FIGS. 7 and 8 are schematic constructional diagrams of conventional examples which have been proposed to solve the above drawbacks of the semiconductor laser.
In FIG. 7, an n buffer layer 12, an n clad layer 13, a non-doped active layer 14, and a p clad layer 15 are formed on an n type substrate 11. Further, a current blocking layer 16 of n-GaAs which is partially opened, a p clad layer 17, a p contact layer 18, and electrodes 19 and 20 are formed.
In such a construction, when a voltage is applied, a current flows from the electrode 19 to the electrode 20. At this time, since it is difficult for the current to flow in the portion of the current blocking layer 16, the currents are concentrated in the opening portion of the current blocking layer 16 as shown by arrows 22.
Further, when a distance 21 between the current blocking layer 16 and the active layer 14 is set to a value such as to cause the light absorption in the current blocking layer 16 in consideration of the leakage of the light from the active layer 14, the light emitting portion is limited to only the opening portion of the current blocking layer 16. Due to this, the laser oscillation can be caused by a low threshold value (typically, 30 to 40 mA).
As practical numerical values of the above laser structure, the distance 21 is set to 0.4 .mu.m, a thickness and a carrier concentration of the current blocking layer 16 are set to 0.6 .mu.m and 6.times.10 cm.sup.-3, and carrier concentrations of the p clad layers 15 and 17 are set to 1.times.10 cm.sup.-3. A width of the opening portion of the current blocking layer 16 is set to 3 .mu.m.
In a semiconductor laser shown in FIG. 8, an n buffer layer 32, a clad layer 33, a non-doped active layer 34, p clad layers 35 and 36, a current blocking layer 41 of n-GaAs having an opening portion, a contact layer 37, and electrodes 40 and 38 are formed on a stairway-shaped n substrate 31.
In the above conventional example as well, the currents are concentrated in the opening portion of the current blocking layer 41 (shown by arrows 39). On the other hand, since there are differences of the refractive indices even in the lateral direction due to the stairway shape, the light is shut up in the stairway portion and a high efficiency can be accomplis
REFERENCES:
patent: 4503539 (1985-03-01), Mori et al.
patent: 4785457 (1988-11-01), Asbeck et al.
patent: 4839307 (1989-06-01), Imanaka et al.
patent: 4932033 (1990-06-01), Miyazawa et al.
Canon Kabushiki Kaisha
Epps Georgia
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