Far‐infrared absorption in amorphous III‐V compound semiconductors

The infrared spectra of amorphous films of GaP, GaAs, GaSb, InAs, and Ge prepared by sputtering have been measured from 10 to 4000 cm −1 . The absorption spectra in the region of the “optical” phonon frequencies show similarities to the phonon density of states as deduced from Raman scattering but the absorption becomes much smaller at low frequencies. It is shown that while the coupling constant for Raman scattering by an amorphous material varies as the square of the wave vector, it varies in the case of infrared absorption as its fourth power. The results are compared with those of Raman scattering and with the predictions of a simple model.