Control of the n-type doping in AlxGa1-xSb: DX-center behavior of the Te impurity

Hall and photo-Hall data have been taken in Te-doped AlxGa1-xSb epitaxial layers of different AlSb molar fractions and doping densities in the 10(17)-10(18) cm(-3) range. The evidence of the persistent photoconductivity effect at low temperatures reveals the presence of the DX center, whose occupancy level is as deep as the AlSb molar fraction increases. The temperature dependences of the Hall carrier density and mobility, n(H)(T) and mu(H)(T), have been carefully investigated by varying the density of the photoionized DX centers between the dark value and the saturation one. At low temperatures the electrical data are dominated by the occupancy of a Te-donor level in thermal equilibrium with the conduction band states, responsible of a semiconductor-to-metal transition when the density of the photoexcited electrons becomes sufficiently high. The isothermal mu(H)(n) curve is a single valued function, independent of the experimental procedure. Possible explanations of this result have been briefly discussed. (C) 1997 Elsevier Science S.A.