CALCULATIONS OF ELECTRONIC AND OPTICAL-PROPERTIES OF SI GE ALLOYS ANDSUPERLATTICES - APPLICATION TO PLANAR WAVE-GUIDES/

A systematic comparative study between the electronic and optical prop erties of the strain layer superlattices (Si)(10-n)/(Ge)(n) coherently grown on a Si1-n/10Gen/10(001) alloy surface and those of the corresp onding bulk alloys Si1-n/10Gen/10 is presented. We find that the super lattices have a smaller fundamental gap than the corresponding alloys; also for energies smaller than 1.5 eV and polarization along the grow th plane, the real part of the dielectric function, epsilon(1), for th e SLS is larger than that of the corresponding alloy, while for perpen dicular polarization, the two dielectric functions practically coincid e. The utilization of this property for the construction of planar wav eguides is investigated. In particular, the transverse electric modes of a waveguide consisting of a finite thickness SLS (Si)(6)/(Ge)(4), s andwiched between two layers of the alloy Si0.6Ge0.4, are studied. No transverse magnetic modes exist in this structure.