Ed Ghahramani

FULL BAND STRUCTURE CALCULATION OF THE LINEAR ELECTRO-OPTIC SUSCEPTIBILITY

We have derived a complete microscopic quantum mechanical expression for the frequency‐dependent (clamped lattice) linear electro‐optic (EO) susceptibility, χ⇊(2) (−ω;ω,0), of crystalline solids in the independent particle approximation. The expression is free of the unphysical divergent terms at zero frequency which often plague such calculations. Using these expressions and utilizing a linear combination of Gaussian orbitals technique in conjunction with the Xα method we have carried out a full band structure calculation of the frequency‐dependent linear EO susceptibility of GaAs. Our calculated results are in good agreement with the available experimental measurements.

Enhancement of zone‐folding effects in the second order response of the [(Si)5/(Ge)5]/(Si0.4Ge0.6)(001) superlattice

We have carried out a full band structure calculation of the second harmonic generation (SHG) coefficient and the linear response function of a [(Si)5/(Ge)5] superlattice (SLS) on a Si0.4Ge0.6 alloy substrate. Our calculation gives the first indication of the magnitude, frequency dependence, and anisotropy of the second order response in this SLS. The ratio of the features due to zone‐folded transitions to those due to bulk‐like transitions is an order of magnitude larger than the same ratio in the linear response. Yet these zone‐folded effects are still very small. Nonetheless, the overall size of the SHG coefficient for this SLS is slightly larger than that of the corresponding SLS on a Si(001) substrate.