Capacitance accumulation layer

The capacitances for the accumulation layer and inversion layer are respectively given by... 

At higher photon energies there is additional structure some of this is as expected, other features less so. There is a relatively weak feature at 1.15 eV which is of the same sign as the 0.SS eV response, with absorption in accumulation and bleaching in depletion. This feature is not directly related to die fmnation of the charge accumulation layer as it shows a very different dependence on bias voltage to both the differential capacitance and the electro-optical response at 0.55 eV, as shown in figure 37, with a peak in response at around +5 V. We do not have an explanation for this feature. 

Electrode surfaces in elec trolytes generally possess a surface charge that is balanced by an ion accumulation in the adjacent solution, thus making the system electrically neutral. The first component is a double layer created by a charge difference between the electrode surface and the adjacent molecular layer in the flmd. Electrode surfaces may behave at any given frequency as a network of resistive and capacitive elements from which an elec trical impedance may be measured and analyzed. 

Here, clayer = Ksjdlayer is the capacitance per unit area (in farads/m2) of the layer. The surface voltage Vlayer can be related to the accumulated surface charge a/ (in C/m2) by the following equation ... 

There are not many models that do transients, mainly because of the computational cost and complexity. The models that do have mainly been discussed above. In terms of modeling, the equations use the time derivatives in the conservation equations (eqs 23 and 68) and there is still no accumulation of current or charging of the double layer that is, eq 27 still holds. The mass balance for liquid water requires that the saturation enter into the time derivative because it is the change in the water loading per unit time. However, this treatment is not necessarily rigorous because a water capacitance term should also be included,although it can be neglected as a first approximation. 

Si(lll) structures formed on n- and p-doped substrates showing the typical accumulation (acc), depletion (dep) and inversion (inv) regimes, (b) Capacitance-voltage curves (1MHz) in the dark (circles) and under white illumination (squares) for a structure formed on a p-doped substrate. The increase in capacitance under illumination in positive bias is characteristic of the formation of an inversion layer. Reprinted from [25]. 

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