The substrate-induced effect of GaN MSM photodetectors on silicon substrate

GaN metal-semiconductor-metal photodetectors (MSM PDs) on silicon substrates and sapphire substrates were fabricated and characterized. We found that the current-voltage (I-V) characteristics of MSM PDs on the silicon substrate could be approximated by the Poole-Frenkel conduction behavior. This phenomenon was attributed to the presence of micro-grain structure in the silicon-substrate epitaxy layer. The voltage-dependent responsivity of GaN MSM PDs on the silicon substrate was also evidence of micro-grains inside the epitaxy layer. At a low frequency, the 1/f-form noise was a main contribution to both PDs. Moreover, the extremely low beta (similar to 0.7) extracted from GaN MSM PDs on the silicon substrate was first reported. Based on the current-voltage behavior, the extremely low beta was believed to originate from the silicon-substrate-induced micro-grain.