| Research Abstract |
The main problem in growing GaAs on Si substrate is the thermal stress produced by the thermal expansion coefficient mismatch, since it significantly affects lifetime of the light emitters. We have proposed UCGAS (undercut GaAs on Si)to combat this problem, and more than 3000 hours of lifetime was demonstrated. Since a thin double-heterostructure (DH) is sandwiched in air in this structure, light produced inside DH is strongly reflected at the surface, light is absorbed in the active layr and is re-emitted from the active layr. The purposed of this research is to investigate this photon recycling effects in UCGAS and to apply this effect to light emitters on Si.
As for the light emitters on Si, the research on the dislocation dynamics has been performed. The dislocation motion in GaAs on Si is monitored, in situ, while applying external stress. The dislocation is found to move for the first time. This may be applied to manipulate dislocation, since the dislocation can be artificially moved by the external stress. This technology is important, because optical devices which is smaller than the averaged spacing of the dislocation density of 10^5 cm^<-2> can be made in dislocation-free regions.
As for the photon recycling experiments, we have tried to fabricate a three dimensional small sphere to confine light within that ball. The research on MOCVD growth mechanism was performed to find a suitable growth conditions to obtain sphere-shaped GaAs in a small grooves fabricated on Si substrate. We could obtain, by selecting growth condition, flat or convex surfaces affer the growth, however, a perfect sphere was not obtained.
The technology developed in this research will be important not only in the application to photon recycling lasers but it also be a basic technology in fabricating optical IC's incorporating both GaAs and Si devices.
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