Charge carrier transport in the electrode-oxide semiconductor interfaces

4 Charge carrier transport in the electrode-oxide semiconductor interfaces 

One of the important issues of semiconductor gas sensors is the understanding of charge transfer reactions at surfaces and interfaces, and of charge transport in oxide semiconductors. Gas adsorption at surfaces of oxide semiconductors may lead to charge transfer reactions and to the change of electrical conductivity in the chemical sensors. This section deals with electrical characteristics, transport mechanism and the layer structure in the metal-semiconductor interface. 

1 Electric field and capacitance in the metal-semiconductor interface 

A closed form solution of this equation is not possible. An additional simplifying assumption made in the analysis is the so-called depletion approximation . In this approximation, the free carrier concentrations are assumed to fall abruptly from their equilibrium values Hq and po in the bulk neutral region to a negligibly small value in the barrier space charge region. In reality, this transition occurs smoothly over a distance in which the bands bend by about 3 kT, but the calculations made using the depletion approximation are sufficiently accurate for most purposes. TIius, using the depletion approximation, Equation [3.26] can be written as  

the potential varies parabolicaUy with the distance in the depletion region and has its maximum value 0(0) = given by  

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