Enhanced Specific Detectivity and UV-to-Visible Rejection-Ratio of Visible-Blind Metal–Semiconductor–Metal Photodetectors, Based on Epitaxial GaN/Si(111)

A very high specific detectivity and UV-to-visible rejection-ratio (UVRR) is reported for visible-blind metal–semiconductor–metal (MSM) photodetectors (PDs), fabricated with gallium nitride (GaN) on Si(111) epitaxial layers. Comprehensive analysis of different figures-of-merit (FOM) reveals that the high specific detectivity results from a large responsivity in the UV-A region of the electromagnetic spectrum, and extremely low dark current, of the PDs. The current transport mechanisms in the absence and presence of illumination suggest that an internal gain, which is attributable to photo-induced barrier lowering, is responsible for the large responsivity of the PDs. The dark current is reduced due to the use of platinum-gold (Pt/Au) Schottky contacts, characterized by a relatively high Schottky barrier height. The vast improvement of nearly all FOMs, compared to those reported earlier for GaN/Si PDs, is highly encouraging for the development of low-cost, large-area arrays of visible-blind PDs.