Conductance Model for Single-Crystalline/Compact Metal Oxide Gas Sensing Layers in the Non-Degenerate Limit: Example of Epitaxial SnO$_2$(101)

TL;DR

This paper develops an analytical conductance model for epitaxial SnO₂ gas sensors, providing fundamental insights into sensing mechanisms by relating conductance changes to surface electrostatic potential, validated through in operando measurements.

Contribution

It introduces a detailed analytical model for single-crystalline metal oxide sensors that clarifies sensing mechanisms beyond polycrystalline models.

Findings

Model accurately predicts conductance based on surface potential changes.

Validation through combined resistance and work function measurements.

Model applicable within the Boltzmann approximation region.

Abstract

Semiconducting metal oxide (SMOX)-based gas sensors are indispensable for safety and health applications, e.g. explosive, toxic gas alarms, controls for intake into car cabins and monitor for industrial processes. In the past, the sensor community has been studying polycrystalline materials as sensors where the porous and random microstructure of the SMOX does not allow a separation of the phenomena involved in the sensing process. This lead to conduction models that can model and predict the behavior of the overall response, but they were not capable of giving fundamental information regarding the basic mechanisms taking place. The study of epitaxial layers is the definite prove to clarify the different aspects and contributions of the sensing mechanisms that are not possible to do by studying a polycrystalline sample. A detailed analytical model for n and p-type single-crystalline/compact metal oxide gas sensors was developed that directly relates the conductance of the sample with changes in the surface electrostatic potential. Combined DC resistance and work function measurements were used in a compact SnO2 (101) layer in operando conditions that allowed us to check the validity of our model in the region where Boltzmann approximation holds to determine surface and bulk properties of the material.