Abstract: The physical meanings and affecting factors of the optimal phase are analyzed and validated systematically in the measurement of surface photovoltage spectroscopy (SPS) based on Lock-In amplifier. Taking the example of p silicon, under different modulation frequencies the measured data of the optimal phase were in agreement with the theoretical analysis, which shows that for the usual metal-insulator-semiconductor (MIS) “sandwich” structure, the equivalent impedance can greatly affect the optimal phase. In the case of bulk materials, the optimal phase only correlates with experimental conductions. But for nanomaterials, the equivalent resistance and capacitance (Rins and Cins) of MIS structure vary under illumination that will result in great changes in the optimal phase. Because Rins and Cins are related to the characters of nanomaterials, the optimal phase may offer a new method for the measurement of photo-electric properties of nanomaterials.

Key words: Surface photovoltage, Lock-In, Optimal phase, MIS structure, Equivalent impedance