Promotion of acceptor formation in SnO2 nanowires by e-beam bombardment and impacts to sensor application

We have realized a p-type-like conduction in initially n-type SnO2 nanowires grown using a vapor-liquid-solid method. The transition was achieved by irradiating n-type SnO2 nanowires with a high-energy electron beam, without intentional chemical doping. The nanowires were irradiated at doses of 50 and 150 kGy, and were then used to fabricate NO2 gas sensors, which exhibited n-type and p-type conductivities, respectively. The tuneability of the conduction behavior is assumed to be governed by the formation of tin vacancies (under high-energy electron beam irradiation), because it is the only possible acceptor, excluding all possible defects via density functional theory (DFT) calculations. The effect of external electric fields on the defect stability was studied using DFT calculations. The measured NO2 sensing dynamics, including response and recovery times, were well represented by the electron-hole compensation mechanism from standard electron-hole gas equilibrium statistics. This study elucidates the charge-transport characteristics of bipolar semiconductors that underlie surface chemical reactions. The principles derived will guide the development of future SnO2-based electronic and electrochemical devices.