In this work we present a detailed study of the influence of the GaAs substrate orientation on the electrical properties of heterojunctions based on GaAs and sulfonated polyaniline (SPAN) using Current-Voltage (I-V), Capacitance-Voltage (C-V), Deep-Level Transient Spectroscopy (DLTS) and Laplace DLTS techniques. Three different GaAs substrate orientations have been investigated, namely (100), (311)A and (311)B. The I-V results revealed that the turn-on voltage (Von) of SPAN/(311)B GaAs heterojunction is higher than that for SPAN/(100) GaAs and SPAN/(311)A GaAs heterojunctions. The DLTS results showed that the number of electrically active defects present in devices based on the lower index (100) plane of GaAs substrate is higher than those of higher index (311)A and (311)B GaAs substrates, corroborating with I-V results. In order to investigate the role of interface states, capacitance-frequency measurements were performed in forward bias on all three devices.

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