DEEP LEVELS IN TE-DOPED ALSB GROWN BY MOLECULAR-BEAM EPITAXY

Deep electron traps in Te-doped AlSb have been investigated by deep level transient spectroscopy (DLTS). The diodes used for DLTS measurement were InAs/AlSb n-N isotype heterojunctions (quasi-Schottky barriers) with excellent rectification characteristics, grown on n+-GaAs substrates by molecular beam epitaxy. In the temperature range investigated, from 90 to 300 K, a number of electron trap levels were observed, not all of them well defined. The best-defined level was found to have a thermal electron emission energy of 0.26 eV, much shallower than the values 0.46-0.48 eV found by Takeda et al. for AlxGa1-xSb alloys with x≤05. This suggests a compositional dependence of the thermal emission energy for the deep electron trap level in AlxGa1-xSb in the range 0.4<x≤1.0, in contrast to the constant value reported for AlxGa1-xAs. Temperature-dependent Hall effect measurements gave an ionization energy of 100 meV, suggesting that EDX decreases with increasing Al content, as in (Al,Ga)As. In a sample doped with Te at a level of 3.1×1017 cm-3, the trap concentration was 2.0×1017 cm -3, indicating that Te-doped AlSb has a much larger number of deep electron traps than n-AlAs.