Title: Impact of surface functionalization on GaN or ZnO nanostructure based hetero-interfaced UV photodetectors

Abstract

The pandemic COVID-19 is causing significant economic, healthcare and social disruption world-wide. The protective vitamin-D synthesis by the Ultraviolet-B (UVB) radiation in human beings found to be major break-through for the betterment of mankind. Therefore, it is inspiring to emphasis on utilization of UVB and fabricates energy efficient and durable ultraviolet-photodetectors (UV-PDs). Henceforth, the presented study showcased the fabrication of unique tapper ended GaN-Nanotowers (GaN-NTs) based highly efficient UV-PDs. Thereby, hexagonal stacked GaN nanocolumnar structure (nanotowers) exhibits higher photocurrent generation which significantly enhances its responsiveness towards UV and leads to outstanding performance of the device. The fabricated detector display low dark current (~ 12nA), high ILight/IDark ratio (> 104), fast time-correlated transient response (~ 433µs). A very high photo responsivity (R) of 2.47 A/W in self-powered (zero applied bias) mode of operation is reported. While in photoconductive mode, the R is observed to be 35.4 A/W@-3V along with very high external quantum efficiency (EQE) is ~ 104%, lower noise equivalent power (NEP) ~ 10-13 WHz-1/2 and excellent UV-Vis selectivity. Besides this, the role of increased thickness of AlN-buffer layer and GaN-NTs height is also realized in terms of enhanced performance PDs. This variation in device geometry leads to augmented R, low NEP, and a high EQE of 88.6 to 484.77 A/W@-3V to -6V, 1.76 × 10−13 W.Hz 1/2, and 1.85 × 105 %, respectively. Moreover, for further improvisation, a hybrid interface of ZnO/GaN with unique geometry of nanostructure over nanostructure is also explored. These ZnO-NRs hybridized GaN-NTs based UV-PDs demonstrated enhancement in R value from 477 A/W to 1204 A/W@-6V. Furthermore, an impact of sensitization of chemically synthesized novel GQDs on a ZnO-NRs/GaN-NTs heterostructure-based UV-PDs is also realized. The fabricated device demonstrates an excellent R of 3200 A/W at −6 V and displays an enhancement of ~671% and ∼265% compared to its bare counterpart (GaN : 477 A/W and ZnO/GaN: 1204 A/W). In addition, the fabricated heterostructure UV-PD exhibits a very high EQE of 1.2 × 106%, better switching speed, and signal detection capability as low as ∼50 fW.