UV activated visible-blind Ga:ZnO photodetectors using the GLAD technique: a comparative study in different gas atmospheres and temperatures

Abstract

‘Visible-blind’ ultraviolet (UV) photodetectors have been fabricated based on self-seeded undoped (ZnO) and 2% Ga-doped ZnO (Ga:ZnO) nanostructures, produced using the glancing angle deposition (GLAD) technique in a pulsed laser deposition (PLD) setup. The GLAD technique assisted in the formation of pores and thereby enhanced the surface-to-volume ratio. Despite the porosity, the nanostructures are highly crystalline and are oriented towards the c-axis of the hexagonal wurtzite structure. The contribution of Ga doping as a charge carrier donor and the surface morphological variation significantly affected the UV photo-detection properties. The Ga:ZnO device exhibited a low dark current and comparatively high photo-to-dark current ratio. Furthermore, an extremely low operational bias voltage (2 mV) promoted the photocurrent significantly, resulting in a high sensitivity of 59 and 210% for the ZnO and Ga:ZnO photodetectors, respectively. The visible-blind character of the detectors was examined by exposing red, green and blue lights onto the samples. The transient photocurrent response under UV exposure was studied in different atmospheres such as in air, vacuum, nitrogen and oxygen for a comparative study on the performances of the photodetectors. The photoresponse in a vacuum was observed to be 5.6 times higher for Ga:ZnO. The transient photoresponse was further tested at a low temperature (10 K) in order to investigate the stability with respect to the temperature variation. Due to intense UV absorption and their defect-free nature, these PLD grown nanostructures prove their stability and performance under diverse environmental conditions and temperature variation.