Electrical properties and photoluminescence of Te-doped GaAs grown by molecular beam epitaxy

The application of PbTe as a molecular tellurium source in the growth of n-type GaAs:Te by molecular beam epitaxy (MBE) has been investigated. We obtained free-carrier concentrations ranging from 2×1016 to 2×1019 cm−3. In particular in degenerate n-type material, excellent 77 K Hall mobilities were achieved. Even at high impurity concentrations (≳1018 cm−3), Te was not found to accumulate at the surface if a true Pb-saturated (n-type) starting material was used as dopant source. Using low-temperature photoluminescence measurements, we further studied the influence of the doping concentration on the shift of the Fermi level and on the radiative recombination across the fundamental gap in heavily n-doped GaAs:Te. Calculations based on the Burstein-Moss shift and on the band tailing effect, as well as a line shape analysis, were performed for a distinct interpretation of the observed luminescence behavior. At concentrations below 5×1017 electrons cm−3, band-acceptor transitions involving residual carbon acceptors act as dominant recombination process. Above 1018 electrons cm−3, however, the luminescence spectra can be well described by indirect transitions between free electrons in the conduction band and localized acceptor-like centers in the deeper tail states above the valence band edge.