Synthesis and characterization of gold nanoparticles doped zinc oxide nanostructures for ultraviolet photodetector application

Abstract

Zinc oxide nanostructures (ZONSs) doped with different noble metallic nanoparticles (NPs) with customized structures, morphologies and optical characteristics have immense fundamental and applied interests. The potential of the gold nanoparticles (AuNPs)-doped with ZONSs for the photodetectors and solar cells applications have rarely been explored. Based on these facts, in this study, a series of AuNPs-doped ZONSs were prepared and characterized systematically via diverse analytical techniques. The effects of the substrates type, thickness, and growth parameters on the structural, morphological and optical properties of the proposed AuNPs-doped ZONSs were determined. In addition, the optimum sample from each series was selected to fabricate the metal-semiconductor-metal (MSM) ultraviolet (UV) photodetector. First, the ZONSs were deposited (at a rate of 0.3 A°/sec) on the borosilicate glass and three types of n-Si (100) (plain, polished and etched with surface treatment) substrates using the versatile radio frequency (RF) sputtering method operated at 300°C, RF power of 100 W, Argon flow of 10 sccm and pressure of (-5) millibar. The layer of thickness of the deposited ZONSs on both substrates were varied in the range of 100 to 400 nm. The optimum substrate was found to be the etched n-Si (n-ESi) with the thickness of 300 nm. Next, the colloidal AuNPs were synthesized inside deionized water (DW) using the laser ablation in liquid technique. In this process, a gold target was ablated using the Nd-YAG laser (1064 nm) operated for 6 minutes at different energies (96.6, 226, 286 and 336 mJ) and fixed frequency of 6 Hz. The formation of the AuNPs inside DW was verified using the high-resolution transmission electron microscopy (HrTEM), field emission scanning electron microscopy (FESEM) and UV absorption spectroscopy. The AuNPs colloidal suspension prepared at laser energy of 286 mJ was the optimum one and selected for doping into ZONSs. Later, the droplets of the optimum AuNPs colloidal suspension were soaked (both at dark and room temperature for 48 hours) on the deposited optimal ZONSs film to achieve the best AuNPs-doped ZONSs useful for the photodetector fabrication, Finally, the silver (Ag) electrodes were deposited on the AuNPs-doped ZONSs film using the RF sputtering to design the MSM (Ag/n-ESi/ZONSs- AuNPs/Ag) UV photodetector. The current-voltage (I-V) characteristics of the obtained photodetector were measured in the dark and under UV light (380 nm) illumination. The photoluminescence spectra of the optimum AuNPs-doped ZONSs showed an intense near band edge UV peak at 380 nm corresponding to the band gap energy of 3.26 eV. The best MSM UV photodetector revealed a very high responsivity (3.05 A/W), good photosensitivity (1044.5), fast response time (0.29 s) and very short recovery time (0.26s). It was demonstrated that the UV photodetector performance of the ZONSs can remarkably be improved via the AuNPs doping. Additionally, carefully adjusting the nature of the substrates, growth parameters of the RF sputtering and laser ablation technique the structures, morphologies, optical and electrical traits of AuNPsdoped ZONSs can tailor the UV photoreactor productions for different applications. The proposed MSM UV photodetectors may be advantageous for various optoelectronic applications.