Space-charge layers on Ge surfaces. II. High-frequency conductivity and cyclotron resonance

We examine the high-frequency conductivity and cyclotron resonance of electrons in a space-charge layer on a Ge (111) surface. It is shown from the frequency dependence of the infrared absorption that the surface carriers are localized or at least strongly perturbed for densities Nₛ1×10¹² cm^-2. The cyclotron resonance shows a shift of the resonance to low magnetic field at such densities. Only above {~}2 ×{} 10¹² cm^-2 is the free-electron cyclotron mass observed.