High-resistivity GaAs double-injection devices have recently been investigated by Ferro and Gandhi. They found a sublinear ``current saturation'' in oxygen-doped n-type material but not in chromium-doped p-type GaAs, causing them to refute an interpretation by the relaxation-case theory in favor of field-enhanced trapping. We demonstrate that simple relaxation-case arguments in fact correctly predict the different behavior. Sublinear current-voltage characteristics as resulting from recombinative space-charge injection are more probable in n-type than in p-type materials by a factor b2, where b is the mobility ratio.
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H. J. Queisser (1972) studied this question.