Quantification of Si dopant in β-Ga₂O₃-based semiconductor gas sensors by total reflection X-ray fluorescence spectroscopy (TXRF)

Abstract

Developing of chemical sensors is relevant for solving environmental problems of monitoring the atmosphere of cities and industrial zones. Semiconductor sensors based on metal oxides are a promising type of chemical gas sensors due to their high sensitivity, low cost, small size, and low energy consumption. First attempts of pilot operation of atmospheric air monitoring systems based on such sensors revealed an insufficient stability of their response. Doping silicon in the basic material can solve the problem. At the same time, data on the amount and distribution of the dopant in the material are necessary to determine the relationship «synthesis conditions – composition – properties». We propose an approach to the determination of the composition of novel semiconductor materials based on β-Ga2O3 with a silicon dopant content from 0.5 to 2 %at. The approach included grinding of samples using a planetary mill and preparation of suspensions in ethylene glycol, followed by TXRF determination of the analytes on sapphire substrates using the method of absolute contents (Si) with Sr 0.08 and the method of external standard (Ga) with Sr 0.04. X-ray fluorescence analysis of the samples was performed on a S2 PICOFOX spectrometer (Bruker Nano GmbH, Germany). MoKα radiation was used to excite X-ray fluorescence. The spectrum acquisition time is 250 sec. It is shown that the homogeneity of the dopant distribution in the material can be estimated using the suspension analysis. The studied materials demonstrate an irreproducible sensory response which we associated with the revealed inhomogeneity of the silicon distribution over the surface of β-Ga2O3.