PSi noise sensors

The sensitivity of gas sensors is mainly measured by the classical method of a comparison of the ohmic resistance of the sensors in gas media and air. However, excellent results have been obtained by studying and comparing the low-frequency noise characteristics of sensors to determine their sensitivity. 

In Paremuzyan and Aroutiounian (2012a, 2012b), the phenomenon of a reduction in the heat of adsorption was taken into account using the results of Langmuir s theory. The noise for oxygen and other type of gases was calculated. 

Measurements of current-voltage characteristics (CVCs) of the above-mentioned structures were carried out at room temperature in air and in mixtures of air with different concentrations of carbon monoxide. The typical CVCs of samples with a porosity of 73% in all environments have a nonlinear behavior. The CVC is nonlinear for low back bias, but becomes linear with an increase in low back bias. The CVCs for PSi of 73% porosity, both in air and in air + 0.4% CO, have rectifying characteristics, but, as compared with the corresponding characteristics of samples with 50%-PSi, a sharp decrease in conductivity and an absence of current saturation took place. The factor of ideality m was estimated from the initial part of the direct branch. The barrier height was determined from the linear part of the backward branch of the CVC. 

A model where the resistance Rs of the heterojunction interface PSi/ Si-single crystal is connected in series with the base resistance of the PSi layer was applied for the study of CVCs. As in the field of small direct bias, the voltage drop is insufficient and displacement on the base resistance may be ignored the initial part of the direct branch is approximated by the exponential dependence of current J on voltage U with a large factor of ideality m  

Here q is electron charge, k is the Boltzmann constant and T is temperature. The factor m can be estimated from Equation [12.1]. 

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