Highly sensitive semiconductor NO x gas sensor operating at room temperature

Abstract

The novel semiconductor NO x gas sensor based on a heterojunction structure workable at room temperature has been investigated. The sensor consists of Pt/Tin-dioxide(SnO 2)/n-Si/p +-Si/Al in which vertical direction current between Pt and Al electrode was measured with applying reverse direction bias voltage on Pt electrode. All the films including SnO 2 with the thickness of 50–200 nm were deposited on an epitaxial layer of n-Si over p +-Si substrate by RF sputtering method. As a result, the current in the sensor decreased when the gas flow was switched from dry air to mixed gas of air and NO x . Clear response was obtained at the NO x gas concentration as low as 1 ppm at room temperature, while the almost no response was observed for the n-Si, p-Si, and p-Si/n +-Si substrate. The generation of large change in current for the sensor was considered that the barrier height change or conductivity change of SnO 2 gas sensitive layer may cause the modulation of the depletion layer at the n/p +-junction of Si substrate.