Preparation and properties of heavily doped and strongly compensated Ge films on GaAs

We present and generalize the preparation conditions and properties of heavily doped and strongly compensated (HDSC) Ge films obtained by deposition in the vacuum onto the semi-insulating GaAs (100) substrates. A possibility of formation of Ge films with various doping levels and compensation degrees (in particular, fully compensated) is demonstrated. Heavily doped and fully compensated Ge single-crystalline thin (similar to 0.1 mu m) films obtained have high resistivity (up to 140 cm), conductance activation energy as high as half the bandgap of Ge, low free charge carrier mobility (similar to 50 cm(2)/V s), and concentration (similar to 10(14)-10(15) cm(-3)). The electrical and optical properties of the films are explained with allowance made for the presence of large-scale fluctuations of electrostatic potential in Ge. Under certain conditions, a two-dimensional potential relief may exist in thin HDSC Ge films, as well as two-dimensional percolation may occur.