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

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 fracti ons in the 0.25 less than or equal to x less than or equal to 0.50 range an d n-type doping of about 10(18) cm(-3). A family of x approximate to 0.40 s amples of different doping (5 X 10(15) - 10(18) cm(-3)) were also studied. The Hall electron density data versus temperature were analyzed at high tem peratures (T greater than or equal to 150 K) where the DX center is at equi librium, by assuming the negative-U model for the DX level and by taking in to account the multivalley conduction effects. The DX level, degenerate in energy with the conduction band at low x values, enters the forbidden gap a t x approximate to 0.25 and then it becomes deeper with increasing x. In li ghtly doped samples, the introduction of a second level of the same Te impu rity is required to fit the data; such level can be identified with the non metastable level which controls the low temperature electrical properties o f the material. A critical discussion on the choice of the conduction band parameters for the fitting is reported. (C) 1999 American Institute of Phys ics. [S0021-8979(99)01601-1].