Trap-assisted enhancement of the responsivity in asymmetric planar GaN-based nanodiodes at low temperature

The microwave detection capability of GaN-based asymmetric planar nanodiodes (so-called Self-Switching Diode, SSD, due to its non-linearity) has been characterized in a wide temperature range, from 70 K up to 300 K. At low temperature, microwave measurements reveal an enhancement of the responsivity at frequencies below 1 GHz, which, together with a pronounced hysteresis in the DC curves, indicate a significant influence of the surface states. This leads to a significant variability and non-repeatability which needs to be reduced since it degrades the accuracy of the detection. For this sake, the RF characterization was repeated after applying a positive/negative voltage able to fill/empty the surface states in order to have a well-established preconditioned state. As a consequence of the positive pre-soak bias, a significant enhancement of the measured responsivity, with a x 10 increase at low temperature. The RF detection measurements after such preconditioning contains a time dependence induced by the slow discharge mechanism of the traps, so that the improved responsivity remains even after 100s of seconds. On the other hand, a negative voltage pre-soak benefits the discharge process, thus suppressing the low frequency dispersion and the important variability of the detection without the pre-conditioning step. We also show that the relation between the voltage and current responsivities in each case allows to explain the impact of the surface charges in terms of the device impedance.