Temperature and frequency dependence of negative differential capacitance in a planar GaN-based p-i-n photodetector

In this work, back-illuminated planar GaN-based p-i-n photodetectors were fabricated by Si implantation into GaN-based p-i-n structure grown by metal-organic chemical vapor deposition (MOCVD). The dark current density of the photodetector is 1.03 nA/cm2 under zero bias. The unbiased responsivity is 0.122 A/W at 360 nm, corresponding to an external quantum efficiency of 42%. Temperature and frequency dependence of capacitance versus voltage characteristics of the photodetectors are also investigated respectively. A novel negative differential capacitance (NDC) effect observed in the photodetector at room temperature under the frequency of 120 kHz or at low temperature under relative high frequency (such as 200 kHz). The NDC effect becomes much more obvious with the temperature or frequency decreased. This novel phenomenon is mainly due to the carrier confinement of the deep level centers in the detector, which mainly include lattice defects formed by high dose ion implantation and subsequent annealing.