Wavelength modulation of the photoresponse near the indirect edges of Si, Ge, and GaP

The wavelength modulation spectra for photovoltage und photoconductivity have been measured near the indirect edges of Si, Ge, and Gap. These measurements show that the structures associated with phonons can be easily resolved by a simple method. The structures corresponding to indirect transitions with emission or absorption of phonons have been observed, and the energies of some types of phonons have been estimated.