Effect of Space Charge Capacity On Gas-reactive Effect In Semiconductor Gas Sensors

Abstract

The paper discusses the mechanism of the appearance of the space charge in the near-surface region of semiconductor gas sensors, which leads to the appearance of a differential capacitance, which depends on the concentration of the measured gases. Solving the Poisson equation showed that the differential capacitance of the space charge of the surface region of semiconductor gas sensors depends exponentially on the surface potential, which varies with the concentration of the measured gases. The capacity of the near-surface layer of the space charge of semiconductor gas sensors depends on the surface potential, the change of which is determined by the effect on the sensor surface by a certain concentration of the measured gases. The change in the reactive component of the impedance of semiconductor sensors to the concentration of the measured gases describes the essence of the gas-reactive effect, in turn, makes it possible to obtain the dependence of the output frequency on the concentration of active gases in self-oscillating transducers. For impurity semiconductors, the dependence of the differential capacitance of the surface layer on the dimensionless electrostatic potential on the semiconductor surface will have a minimum bias for n-type samples towards negative, and for p-type samples — towards positive values of surface electrostatic potential.

Experimental studies of the dependence of the capacitance of the gas sensor of the ACE type, made in Ukraine, on the change in methane concentration at different supply voltages of the autogenerator converter showed a sufficient change. The study was conducted on the basis of the frequency method, in which the gas concentration is converted into a frequency output signal.

The experimental dependence of the change in the capacitance of the spatial charge layer of the gas sensor on the change in methane concentration, acts on the sensor, which confirms the theoretical variation of the capacity of the space charge on the change in surface potential, which varies from units to sixty picofarads.