Abstract

The possibility of (noncentrosymmetric) bulk dipole-allowed (BDA) ${\overleftrightarrow{\chi }}^{\left(2\right)}$ in short-period Si_mGe_n strained-layer superlattices (SLS) has been proposed theoretically [1]. However, the all-important characteristic features of even-odd period dependence and the two-fold sample azimuthal symmetry of the SH signal were not observed in the recent experiments, even for samples grown on vicinal surfaces with biatomic height steps. [2,3] This discrepancy was attributed to the insufficient growth accuracy in SLS periodicity in their samples, resulting in cancellations from microscopic anti-phase domains.³

© 1996 Optical Society of America