Far infrared absorption of amorphous GaAs and Ge

A Discussion on the PhononDensity of States of Amorphous Germanium for the Infrared Range

“…However, below 50cm -1 there is no agreement between our results and experiment after Ref. [6]. On the other hand, extrapolation of our method to other amorphous semiconductors is feasible so that it is possible to derive formulae which become appropriate to explain some features of these materials which may be regarded as unexplored aspects.…”

Electrons and phonons in amorphous semiconductors

“…All of the I R activity, on the other hand, is disorder-induced and presumably the various peaks should be of comparable magnitude. A similar relationship between a ( w ) [35] and SR(o)…”

“…Fig. 4a thus shows S,(w)/w2 [44] anda(o)/w4 [35] for amorphous Ge. Between 70 and 110 cm-1 the agreement is striking.…”

“…The most striking difference is the magnitude of the I R activity in the two low-frequency bands (at z180 and 300 cm-1) relative to the peak response a t ~4 8 0 cm-1. An explanation, suggested independently by Lucovsky [34] and Stimets et al [35], is that the Raman scattering near 500 cm-1 is mainly derived from the same process that is allowed for the TO mode in the crystal and as such is stronger than the disorder-induced scattering a t lower frequencies. All of the I R activity, on the other hand, is disorder-induced and presumably the various peaks should be of comparable magnitude.…”

Far Infrared Absorption by Tetrahedrally Bonded Amorphous Semiconductors

“…The relevant selection rules are relaxed in the amorphous phase, and in principle it is possible to obtain vibrational state densities from absorption spectra. In practice this has not been possible, for the frequency (or mode) dependence of the photonvibration matrix element is not known, and indeed early measurements (Stimets et al 1973;Brodsky and Lurio 1974;Taylor et al 1976) showed that this matrix element depends critically on sample preparation.…”