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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. [ABSTRACT FROM AUTHOR]

In this work it is demonstrated that the presence of surface electric fields during a post-deposition anneal can impact the chemical passivation of SiO2 + SiNx double layer stacks. Although the surface passivation generated in such dielectrics is well known, we demonstrate that an electric field present in the dielectric not only modifies the surface carrier concentration but can also induce a chemical change in the interface properties upon annealing. By tailoring the surface electric field in the dielectric stack prior to annealing, it is shown that the capture rates at the Si-SiO2 interface can be modified depending on the field polarity and magnitude. Planar FZ specimens are examined here. It is found that annealing in the presence of a field pointing into the Si surface, as intrinsically occurs in positively charged SiNx, increases the dielectric charge density without any substantial changes in the chemical passivation. When an opposite electric field is established by negative charge on the dielectric, the chemical passivation worsens substantially where a fourfold increase in the capture rate of minority carriers is obtained via electrical characterisation. We hypothesise that the electric field may be driving atomic hydrogen away from the interface, thus damaging the passivation. [ABSTRACT FROM AUTHOR]

Highly passivating, hole selective contacts are required for future high efficiency silicon solar cells. This work investigates selected dielectrics as potential SiOx replacements to act as hole selective contacts. AlOx and SiNx were identified as good candidates due to their low valence band offsets to silicon and proven surface passivation capabilities. Simulated J-V curves show AlOx and SiNx maintain acceptable contact resistivities at thicknesses below 1.4 and 1.7 nm, respectively. The SiOx hole contact was found to become extremely resistive even at thicknesses <1 nm, suggesting that either pinholes dominate conduction, or the band offset parameters differ from those in real TOPCon structures. The passivation of the dielectrics was also simulated, with SiOx outperforming both AlOx and SiNx primarily due to the excellent interface. Additionally, the effect of nanolayer built in charge was investigated. Charges below 1012 q/cm2 were found to have little effect, while negative charges above 1012 q/cm2 resulted in reductions in the contact resistivity and recombination current. The calculated selectivity for a 1.4 nm layer of AlOx was 12.9, while a value of 13.8 was calculated for SiNx at typical intrinsic charge levels. [ABSTRACT FROM AUTHOR]