Detailed electrical characterisation of the deep Cr acceptor in GaAs

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Abstract
DLTS and ODLTS measurements in p-type and n-type LPE GaAs have been used to characterise the deep Cr acceptor level. Both its electron and hole emission rates have been determined separately. Together with previous determination of electron and hole capture cross sections, these measurements lead to a coherent description of the deep Cr level, which is shown to correspond to the Cr3+ or Cr2+ states according to its electronic filling. The Fermi function of the level has been deduced from these experimental results without any approximation. Furthermore, it is shown that the concentration of the Cr level can be determined not only in p-type GaAs, but also in n-type material from ODLTS measurements using only a Schottky diode. Comparison with results of chemical analysis allows us to conclude that most, if not all, the Cr atoms are electrically active in GaAs.