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 epitax ial layers of different AlSb molar fractions and doping densities in t he 10(17)-10(18) cm(-3) range. The evidence of the persistent photocon ductivity effect at low temperatures reveals the presence of the DX ce nter, whose occupancy level is as deep as the AlSb molar fraction incr eases. The temperature dependences of the Hall carrier density and mob ility, n(H)(T) and mu(H)(T), have been carefully investigated by varyi ng the density of the photoionized DX centers between the dark value a nd the saturation one. At low temperatures the electrical data are dom inated by the occupancy of a Te-donor level in thermal equilibrium wit h the conduction band states, responsible of a semiconductor-to-metal transition when the density of the photoexcited electrons becomes suff iciently high. The isothermal mu(H)(n) curve is a single valued functi on, independent of the experimental procedure. Possible explanations o f this result have been briefly discussed. (C) 1997 Elsevier Science S .A.