Impact of post deposition annealing of ZrO2 insulating layer on the performance of GaN metal-semiconductor-metal ultraviolet photodetectors

GaN metal-semiconductor-metal (MSM)ultraviolet photodetectors without and with annealed ZrO2 insulating layers are successfully fabricated. It is found that the dark current is reduced by 3 times post annealing of the oxide layer. GaN MSM photo detectors exhibit large internal gain which can be explained by considering the presence of hole traps in oxide layer. Further, reduction in gain and increase intransient response time of photodetectors post annealing of ZrO2 layer reveal that the density of shallow trap states is considerably reduced by the annealing step. It is noticed that though the response of all the states is affected by the annealing but the fast component of photo response is rather severely hampered. The present investigations clearly demonstrate that reduction of dark current is not the sole criteria for improving the performance of a photodetector. Rather, transient response of the device and hence the bandwidth of the device along with the leakage current and gain should be taken into consideration for qualifying the overall performance of the photodetectors.