Future of Al_xGa_1-xN materials and device technology for ultraviolet photodetectors

Thanks to advances in the quality of wide bandgap Al_xGa_1-xN semiconductors, these materials have emerged as the most promising approach for the realization of photon detectors operating in the near ultraviolet from 200 to 365 nm. This has in turn spurred the need for such devices in an increasing number of applications ranging from water purification to early missile threat warning systems. Nevertheless, the control of the material quality and doping, and the device technology remain tremendous challenges in the quest for the realization of high performance photodetectors. Design of the photodetector structure is one of the key issues in obtaining high performance devices; especially the thickness of the intrinsic region for p-i-n photodiodes is a crucial value and needs to be optimized. We compare the performance of the p-i-n photodiodes with different widths for the depletion region, which shows a trade-off between speed and responsivity of the devices. Furthermore, another challenge at present is the realization of low resistivity wide bandgap p-type Al_xGa_1-xN semiconductors. We present here recent advances and propose future research efforts in the enhancement of the Al_xGa_1-xN p-type conductivity through the use of polarization fields in Al_xGa_1-xN/GaN superlattice structures.