Formation of two-layer composite-on-insulator structures based on porous silicon and SnO$_x$. Study of their electrical and gas-sensing properties

The objective of this work is to fabricate and study multilayer “composite-on-insulator” sensor structures based on porous silicon and nonstoichiometric tin oxide. Two-layer structures “macroporous silicon-mesoporous silicon” on single-crystal silicon with sharp geometrical boundaries are grown. Test “composite-on-insulator” structures are fabricated. Oxide on macroporous silicon walls and a buried layer of oxidized mesoporous silicon play the role of the insulator. Nonstoichiometric tin oxide deposited onto the extended surface of oxidized macroporous silicon by chemical vapor deposition (CVD) is the sensitive layer. The gas sensitivity is studied upon exposure to NO$_2$ and degassing in air at room temperature. The sensitivity of the por-Si/SnO$_x$ composite structures is higher than the sensitivity of tin-oxide film samples.