A technique for modulation of the reflectance of germanium in the 2–3-eV range by means of a periodically gated electron beam is described. The relative reflectance curves resemble the thermoreflectance results, but the amplitude varies with the one-third power of the excess carrier density. The results agree with a theory that at large excess carrier densities the mean distance between carriers is small enough to cause a modification of the crystal potential and therefore to lower critical point transition energies.
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McCoy et al. (1968) studied this question.