Characterization of ZnO UV photoconductors on the 6H-SiC substrate

Photoconductors based on wide band gap semiconductors are potential devices for UV light detection due to internal photoelectrical gain and fabrication simplicity. Photoresponses of photoconductors based on GaN and ZnO show high values in UV range under large biases and relatively low values in visible range. Although photoresponse of ZnO photoconductors is similar to that of GaN-based photoconductors, mechanisms of photoconductance between two materials are very different. This difference can be found in optical power dependence of photocurrent and I-V characteristics, and has an impact on device design. In this paper we report experimental studies of photoresponse for newly developed ZnO photoconductors. The ZnO film was grown on a 6H-SiC substrate by hybrid beam deposition. The photoconductor device is formed with interdigitated finger-shaped Ti/Au ohmic contacts on the ZnO film. Electrical characteristics, spectral photoresponse, and persistence properties were studied for the device under variable biases. We find that there are at least three mechanisms involved in the device. At low biases and low incident light power, the photoresponse is mainly due to photocreation. At higher light power and lower biases, the space charge regions are responsible for the photocurrent. At higher biases, the contribution from surface states is dominant.