Surface properties of semiconductors from post-illumination photovoltage transient

Abstract

Free surfaces of semiconductors respond to light by varying their surface voltage (surface band bending). This surface photovoltage may be easily detected using a Kelvin probe. Modeling the transient temporal behavior of the surface photovoltage after the light is turned off may serve as a means to characterize several key electronic properties of the semiconductor, which are of fundamental importance in numerous electronic device applications, such as transistors and solar cells. In this paper, we develop a model for this temporal behavior and use it experimentally to characterize layers and nanowires of several semiconductors. Our results suggest that what has previously been considered to be a logarithmic decay is a rather rough approximation. Due to the known limited frequency bandwidth of the Kelvin probe method, most previous Kelvin-probe-based methods have been limited to “slow responding” semiconductors. The model we propose extends this range of applicability.