Dark current characteristics of thermally treated contacts on GaN-based ultraviolet photodetectors

The III-V nitrides (GaN and AlGaN) are being actively investigated recently for its potential as ultraviolet (UV) photodetector materials. One of the most important considerations in fabricating a photodetector is achieving a low dark current condition, which is critical in producing UV photodetectors with a high signal-to-noise ratio. For this purpose, thermal treatment has been proven to be a useful method in reducing the leakage current in a Schottky contact, as well as reducing the dark current in a Schottky contact based metal-semiconductor-metal (MSM) photodetector. In this work, GaN based MSM photodetectors (photodiodes) with nickel (Ni) Schottky contacts were fabricated and characterized. The application of thermal treatment to the contacts at various annealing temperatures (400-700 °C) was investigated. Cryogenic cooling after heat treatment was also performed to determine the effects of this treatment on the electrical characteristics of the devices. Electrical and morphological characterization was performed by current-voltage (I-V) and atomic force microscopy (AFM) measurements, respectively.