In this work, we report a new approach to characterise interface state density (Dit) near the band edges. Interface defect states are known to trap charge carriers via SRH statistics. At dielectric-silicon interfaces charge in the dielectric layer is neutralised by a layer of mirroring carriers in bulk Si, resulting in an accumulation or inversion layer. Since the interface state density increases exponentially towards the band edge, these states can store large concentrations of charge and alter the carrier concentration at the semiconductor surface. This dramatically influences the operation of devices based on surface carrier manipulation, including field effect passivation, inversion layer pn junctions, and field effect transistors. Unlike capacitive techniques, our method allows a very sensitive detection of the concentration of donor- or acceptor-like states in the unavoidable band-tails. Device simulations show that the conductivity of the charge-induced layer is highly sensitive to Dit near the band-tail but is insensitive to Dit−midgap. Therefore, the wafer resistance detected by inductively coupled measurements is used as a metric to detect band-tail Dit. The wafer resistance is recorded while monitored amounts of surface charges are introduced. The band-tail Dit is extracted by fitting the observed resistance dependence to an accurate model of the system. This method allows probing band-tail Dit near both the conduction and valence band edge on either n-type or p-type silicon substrates. Since a lifetime tester is used to record wafer resistance, this technique provides an easy and accurate detection of band-tail Dit. This technique is highly relevant for analysis of photovoltaic devices since it provides a route to better understand the properties of semiconductor-dielectric interfaces crucial to cell operation.
