Research on GaSb/AlSb Multi-Quantum Well Superlattices.
CALIFORNIA UNIV SANTA BARBARA DEPT OF ELECTRICAL AND COMPUTER ENGINEERING
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Multi-quantum-well Gallium AntimonideAluminum Antimonide superlattices SLs with well widths ranging from 12mm down to 1.2nm were grown by molecular beam epitaxy MBE, and their photoluminescence PL properties were studied. From the photoluminescence data it was concluded that the gamma-valley of the GaSb band structure gets pushed above the L-valleys for well widths below 3.8nm, rather than already below 9nm, as was previously thought. For well widths below the direct-to-indirect crossover, the direct-gap luminescence dropped in intensity by over two orders of magnitude, but remained visible down to the narrowest wells studied, with a strength comparable to the presumably phonon-assisted weak indirect-gap luminescence originating from the lower L-valleys themselves, which was also clearly observed. The photoluminescence decay times of the direct-gap luminescence increased from less than 1ns in the direct-gap range to about 100ns in the indirect-gap range, indicating that the direct-gap luminescence in the indirect-gap range cannot be due to primary electrons initially captured by the gamma-valley and surviving there, but must be due to electrons from the lower L-valleys somehow being lifted back up into the gamma-valley. The energies and temperatures involved rule out a thermal re-excitation process, and suggest an Auger-like process, but the details of the latter remain obscure. The indirect-gap luminescence from the L-valleys overlapped with a board luminescence band at lower energies, the origin of which could be traced to the defective wells near the interface between the superlattice and the AlSb buffer layer. It was absent in the remainder of the superlattice.
- Quantum Theory and Relativity
- Solid State Physics