Role of native defects for methane sensing in III-nitride nanostructures near room temperature

The underlying physicochemical processes involved in a chemical or gas sensor device operation are adsorption of chemical molecules, subsequent transfer and transport of charge on semiconductor surfaces. Owing to the high surface-to-volume ratio at the nanoscale, the semiconductor nanostructure surface usually shows complex behavior towards the above three fundamental processes, and hence alters the device performances unambiguously. We present a detailed study conducted on 1-D semiconductor nanostructures, in the context of understanding the above mentioned physicochemical processes which occurs during gas the sensing process. GaN and AlGaN nanowires (NW) with impurity (oxygen) induced surface defects are considered for this study. The experiments and density functional theory (DFT) based simulations of electron energy loss spectroscopy (EELS) studies are performed to understand the type of possible oxygen defects present in the impurity incorporated III-nitride NWs. The global resistive gas sensing measurements are performed on ensemble NW devices under methane gas. Charge transfer process in single GaN NW under methane exposure is studied by in situ scanning Kelvin probe microscopy. The global gas sensing behavior of ensemble NW is understood in terms of impurity induced defect complex (V_Ga-3O_N) mediated localized charge transfer process in single NW. An enhanced sensing response is obtained in case of AlGaN as comparison to that of the pristine GaN NW at near room temperature (50 °C) because of excess amount of carriers generated in the strong influence of native defects. Photoluminescence studies confirmed the presence of native defects in the AlGaN samples. (author)