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Theoretical and experimental research. The gas reactive effect is understood

as the dependence of the total resistance of semiconductor primary analogue gas-
sensitive sensors on the change of measured gases. The change of the active component
of total resistance leads to the change of the negative differential resistance, and the
change of the reactive component changes the capacity of the oscillating circuit of
autogenerator gas transducers, which eventually leads to a unique dependence of the
output frequency of autogenerator devices from the change of concentration of
measured gases. Semiconductor analog gas sensors have a number of drawbacks, such
as low output signal, low accuracy and sensitivity, the need for amplifier devices and
analog-to-digital converters in further signal processing, the parasitic effect of one
measurement channel on another channel, which can be eliminated by using the
method of converting the physical quantity to the frequency [2, 7, 8]. When using the
frequency conversion method, it is necessary to know the dependence of the impedance
of the primary analogue semiconductor gas sensors on the action of measured gases
and the effect of this effect on the output frequency of autogenerator gas transducers.

Physical processes occurring on the surface of semiconductor gas-sensitive

sensors when they interact with measured gases are described by the Poisson equation.
This equation describes the distribution of electrostatic potential in a spatial charge
layer in a near-surface layer of a semiconductor. A sample of a semiconductor of a gas-
sensing element in normal conditions must be electrically neutral. Where it follows that
the surface charge Q

must be compensated equal and opposite to the sign of the charge

in the near-surface layer of the semiconductor. This charge shields the volume of the
semiconductor from penetration into it of an electric field and consists of
semiconductor located in the volume of ionized donor and acceptors and mobile
electrons and holes. Thus, the surface layer of the semiconductor is a layer of spatial
charge that shields the volume of the semiconductor from the electric field of the
surface charge, and this shielding is carried out due to the fact that the equilibrium
concentration of electrons and holes in the layer differs from the bulk. A more complete
and precise solution of the Poisson equation is made in the work of Garrett and Brattain,
the translation of which is made in the monograph [9]. In this paper, we consider a
general case of a semiconductor that is under the influence of excitatory factors such
as illumination, radiation. In the future we will proceed from the most widespread
version of the calculations, which is presented in the monograph of A.V. Rzhanov [10].

Determine the complete near-surface resistance of a Z

semiconductor gas-sensing

sensor in general form, assuming that it represents a parallel connection of the near-
surface C

capacitance and the active surface-to-ground resistance R

)





, (1)

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