Ultralow Dark Current and High-Speed GaN-Based Visible Blind UV Photodetector

This article presents a critical analysis of the fabrication and characterization of a gallium nitride (GaN)based visible-blind metal–semiconductor–metal ultraviolet photodetector. The GaN epilayer exhibits an excellent crystalline quality, as evidenced by symmetric and asymmetric x-ray rocking curve (XRC) full-width at half-maximum (FWHM) values of $\sim 60$ and $\sim 223.2$ arcsec, respectively, along with an average threading dislocation density in the order of $\sim 10^7$ $\mathrm{cm}^{-2}$ as derived from XRC data. Atomic force microscopy analysis reveals a root mean square (rms) roughness of $\sim 424$ pm, further highlighting the smoothness of the epilayer. The high crystalline quality significantly reduces the leakage (dark) current, measured as $3 \times 10^{-12} \mathrm{~A}$ at 15 V, one of the lowest as compared to the already reported devices. The photocurrent with 360 nm input illumination was obtained to be $1.2 \times 10^{-7} \mathrm{~A}$ at 15 V, approximately four orders of magnitude higher than the dark current. The photodetector demonstrates exceptional performance metrics, including a detectivity of $6 \times 10^{12}$ Jones and a responsivity of $0.522 \mathrm{~A} / \mathrm{W}$ at 15 V, surpassing many other recent reports. Also, it features an unmatched ultrafast temporal response with rise and fall times of $\sim 31$ and $\sim 27 \mu \mathrm{~s}$ , respectively, setting a benchmark for high-speed operation.