Photostriction Effect in Germanium

Abstract

Abstract A new optico‐acoustic phenomenon in germanium is reported. A change in the lattice constant (crystal dilatation) is observed when excess pairs of current carriers have been introduced into the sample by monochromatic illumination. The method of measurement enables one to detect small vibrations of the sample with amplitudes down to 10 −11 cm. The effect has been measured in the range from 80 to 1780 cps, and shows no dependence on frequency. The ratio of relative change of the lattice constant to the carrier pair concentration has been estimated to be about 7 × 10 −24 cm 3 which is in satisfactory agreement with the value predicted by theory. Some features of spectral response of the effect can be explained in terms of 〈100〉 exciton states with relatively long apparent lifetimes.