Is shown, that the shift of the second derivative of the current - voltage characteristic of the testing signal frequency dependes on the sort of gas and the concentration of gas in an atmosphere.
A feature of the measuring technique was that at the measurement of current - voltage characteristics on the DC is padding the alternating voltage by the amplitude less than 0,1 V at the frequency range 100 - 1500 kHz was applied. The technique of research allowed to measure not only current - voltage characteristic on DC, but also second derivate of the current- voltage characteristics. So we can use the hardware differentiation of the non-linear current- voltage characteristics for the obtain additional possibilities for the gas sensors creation. In our work the results of the researches of the sensitivity and selectivity of the heterostructure formed by contact of the nanocrystal dioxide (SnO2) and silicon (Si) are presented. The response of the given structure was observed as the change of the second derivative of the current-voltage characteristic. Air, pairs ethyl alcohol and ammonia were used as researched gases.
Results of the researches have shown that with change of parameters of the environment in which the structure is placed the frequency of response is maximal. Besides it has been established that the response of the structure has resonant character. In other words there are frequencies on which the amplitude of the second derivative have the maximum volume and this frequnces are different for different gases. The research of the influence of the different concentration of the gas environment (ammonia) illustrates that the response of the structure changes of the amplitude of the second derivative. Thus, it is possible to speak about selectivity and sensitivity of researched structure to the researched gases to be shown as change of frequency and amplitude of the resonant response at the tamperature equal 300 K.

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