Occupancy level of the DX center in Te-doped AlxGa1−xSb

Abstract

Hall effect measurements were performed in Te-doped AlxGa1−xSb layers grown by molecular beam epitaxy to investigate the composition dependence of the DX center occupancy level. The investigated samples have AlSb molar fractions in the 0.25⩽x⩽0.50 range and n-type doping of about 1018 cm−3. A family of x≈0.40 samples of different doping (5×1015–1018 cm−3) were also studied. The Hall electron density data versus temperature were analyzed at high temperatures (T⩾150 K) where the DX center is at equilibrium, by assuming the negative-U model for the DX level and by taking into account the multivalley conduction effects. The DX level, degenerate in energy with the conduction band at low x values, enters the forbidden gap at x≈0.25 and then it becomes deeper with increasing x. In lightly doped samples, the introduction of a second level of the same Te impurity is required to fit the data; such level can be identified with the nonmetastable level which controls the low temperature electrical properties of the material. A critical discussion on the choice of the conduction band parameters for the fitting is reported.