The study of amorphous semiconductors is of great interest because they find important applications in many electronic devices, like large area solar cells and photosensors. We have developed a methodology for the analysis of transient response of amorphous photodiodes when switched off from steady-state and when they are exposed to a δ pulse of light. For this purpose continuity equations and the transit time effect have been calculated. For the p-i-n photodiodes, characteristics of photo current decay have been analyzed for an ideal case in which the diode is assumed to have a unit current gain. It is found that characteristics either due to decay from steady-state or due to light pulse excitation is transit time dominated. The short-circuit performance of solar cells resembles to a p-i-n diode because a solar cell is essentially a p-i-n diode which is used as an energy converter. Thus short circuit current decay of solar cells behaves similar to the photocurrent decay of the diode and the same method of analysis can be applied.
The study has been carried out for the transient response of photosensors fabricated by amorphous semiconductors under variable levels of excitation when switched off from steady-state. The curves for the entire range of the transient have been plotted in the terms of photoconductivity and they can be converted to current decay curves by multiplying with the applied electric field and the cross-sectional area of the sample. For this purpose, in the calculations, the transit time effect is included. Also, the switching time and gain of the photoconductor have been calculated. It is found that the current gain of the device increases as the density of thermal equilibrium electrons is made higher, compared to that of holes by moving the Fermi level upward. However, this also increased the switching time and its performance, as a switch becomes poorer.
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