What are the semiconductor chemical sensors

Let us start with a definition. Semiconductor chemical sensor is an electronic device designed to monitor the content of particles of a certain gas in surrounding medium. The operational principle of this device is based on transformation of the value of adsorption directly into electrical signal. This signal corresponds to amount of particles adsorbed from surrounding medium or deposited on the surface of operational element of the sensor due to heterogeneous diemical reaction. 

Starting with this definition the semiconductor diemical sensors can be arbitrary classified with respect to following features the type of electrophysical characteristics diosen for monitoring, such as electric conductivity, thermal-electromotive force, work function of electron, etc. type and nature of semiconductor adsorbent used as an operational element of the sensor and, finally, the detection method used for monitoring the adsorption response of electrophysical characteristics of die sensor. 

In eadi specific case the choice of an adsorbent, electrophysical parameters and the method of registration of its change as well as the choice of various pre-adsorption treatment techniques of the surface of adsorbent is dictated by the type and nature of analytical problem to be solved. For instance, if particles active from the standpoint of the change in electrophysical parameters of semiconductor adsorbent occur on the surface of the latter due to development of a chemical reaction involving active particles, it is natural to use either semiconductor material catalyzing the reaction in question or if this is not possible specific surface dopes accelerating the reaction. Above substances are used as operational element of the sensor. If such particles occur as a result of adsorption from adjacent volume, one can use semiconductor materials with maximum adsorption sensitivity to the chosen electrophysical parameter with respect to a specific gas as operational element. 

Semiconductor chemical sensors are characterized by low cost, small size, extra high sensitivity (often unattainable in other analytical techniques) as well as reliability. Moreover, concentration of particles detected is being transformed directly into electrical signal and electronic design of the device is the simplest one which can be arranged for on the active part of the substrate. 

The crystalline structure of adsorbents directly influences their gas sensitivity. Depending on the type of the problem to be addressed ad-sorption-sensitive semiconductors are monocrystals or monocrystal films with a predetermined crystallographic orientation of of erational surface vacuum baked polycrystalline films, which, from their electrical standpoint, are similar to monocrystals but differ from the latter by ulti- 

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