Paper Title
Frequency-Dependenterror of Forward Bias Capacitance Spectroscopyin the Density of States Calculation of Semiconductor Diodes

Abstract
Admittance spectroscopy is a powerful tool for the characterization of semiconductor materials. As for the pin diodes, where three subsequently grown semiconductor layers exist, there is no accepted method to elucidate all the unknown parameters. This is mostly due to the complexity of the measured response signal andthe difficulty to discriminate where the admittance signal comes from.Despite these bottlenecks, the capacitance spectroscopy of pin diodes cannot be overlookedsince it includesvery valuable informationto be extracted for device characterization. In our recent work [1], we have shown that the capacitance-frequency-voltage spectra of a forward biased amorphous silicon pin diode can be used to evaluate the density of states of its intrinsic layer. The capacitance-frequency curves measured when the pin diode is under reverse bias simply give outthe geometrical capacitance, while the forward biased diode exhibits an interesting behavior:i.e. increasing capacitance when the frequency is decreased, anda sudden drop down to huge negative capacitance values below particular frequencies for each dc bias. In our method, the peak points of the capacitance-frequency-voltage curves are used. These maximum capacitance values are thought to be reached when all the gap states at a particular energy level are filled andfurther decrease in frequency leads to the recombination of excess carriers within the intrinsic layer. It is seen that the signal quality in the capacitance-frequency data decreases with decreasing frequencies. Therefore, it becomes difficult to determine both the peak capacitance and its position in the frequency axis, increasing the error in the evaluation procedure. To overcome this problem,extrapolation of the data points around the peak region with an asymptotic approach can be considered. Keywords - Amorphous silicon pin diode, forward bias capacitance spectroscopy, density of states