Theory of multiphonon spectra in semiconductor point contacts

We construct a theory of the nonlinear electrical conductivity of semiconductor point contacts that takes into account current carrier scattering and the electron–phonon interaction. We show that inelastic relaxation processes play a very important role in point contact spectra. Such relaxation arises from the successive emission of a number of phonons by hot electrons (multiphonon relaxation); the emission occurs a distance r from the contact, where r ∼ λϵ ≫d (d is the characteristic dimension of the point contact and λϵ is the electron inelastic relaxation distance). As a result the point contact spectrum contains peaks at multiples of the emitted phonon frequencies and at sums of those frequencies. This conclusion is in complete agreement with the experimental results of Pepper [M. Pepper, J. Phys. C 13, L709 (1980); J. Phys. C 13, L717 (1980)] for a metal–semiconductor heterocontact.

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