Photoresponse of asymmetric planar GaN-based nanodiodes at low temperature

The direct gap of GaN (3.4 eV) and the existence of surface states (either on the top of the AlGaN layer or at the sidewalls of etched trenches) affecting the conductivity in AlGaN/GaN-based nanodiodes result in a strong photodetector performance. This paper analyzes the link between the modifications of the surface states occupation and the optoelectronic response of such self-switching diodes (SSDs) with measurements performed in a temperature range of 70-300 K using a violet laser which covers most of the energies located at the GaN bandgap. The test device consisted of an SSD with a single channel, 1 µm long and 80 nm wide. The measurements revealed a notable photoresponse, taking values of 140 mA W^-1at 100 K, which decrease considerably to 20 mA W^-1at 300 K because of the thermal discharge of the surface states. The results obtained evidence the key role played by the illumination-induced modulation of the surface states occupation in the significant photoresponse provided by the SSDs.