POLARIZATION MEMORY INDUCED BY POLARIZED LIGHT-ASSISTED ANODIZATION OF N-TYPE SI

We report a study on the polarization memory effect in n-type, micropo rous Si anodized in the presence of above-bandgap light. Using unpolar ized light, the memory effect parameter rho=(I-parallel to-I-perpendic ular to)/(I-parallel to+I-perpendicular to) is quite small, reaching v alues of only 5% at the upper end of the photoluminescence (PL) band e xtending to 2.3 eV for excitation with 3.8 eV light. When the same ano dization is carried out under linearly polarized light, the value of r ho increases fourfold to similar to 20% at 2.3 eV. The enhancement is maximal when the pi, is excited with the linear polarization aligned w ith direction of that of the etching illumination. A well-defined anis otropy of rho in the (100) sample plane is found tied to the polarizat ion direction of the etching light and independent of the crystal axes ([100] or [110]). We discuss these observations in terms of a texture of the porous layer with preferential alignment induced by the polari zed light-assisted etching.