Indirect Exciton Absorption in Germanium

Abstract

The indirect exciton absorption in germanium has been investigated using a high-sensitive wavelength modulation technique. The spectrum shows that the structures of indirect-allowed and -forbidden transitions have been clearly identified. It has been established experimentally that the L O phonon-assisted indirect transition is attributed to a forbidden transition, as expected by considerations of the selection rule. The T A phonon-assisted indirect exciton absorption spectrum is interpreted as due to a type of indirect transition which has the optical process for vertical direct transitions allowed and the scattering process for electron-phonon interaction forbidden: the intermediate state in the virtual transition is attributed to \(\varLambda_{3}\) state, whereas the allowed L A phonon-assisted transition is related to the lowest \(\varGamma_{2}{'}\) intermediate state.