Presentation Details
| Understanding the Electron Paramagnetic Resonance Signal of Free Electrons in Passivated Silicon Surfaces Thien Truong1, Chirag Mule1, 2, Rabin Basnet3, P.Craig Taylor2, Sumit Agarwal2, David Mulder1, William Nemeth1, David Young1, Paul Stradins1. 1National Laboratory of the Rockies, Golden, CO, USA.2Colorado School of Mines, Golden, CO, USA.3Australian National University, Canberra, Australia |
Abstract
This work investigates the electron paramagnetic resonance (EPR) signals due to Si surface passivation by, silicon nitride (SiNx) and aluminum oxide (AlOy) layers, used in silicon photovoltaics. Distinct differences are observed in the EPR spectra of SiNx- and AlOy-passivated samples. Narrow-field EPR scans at ~20 K over 3300–3400 Gauss range reveal a clear free-electron resonance at ~3350 G (g ≈ 2) in SiNx-coated samples, which is absent in AlOy-coated samples. Band-structure simulations using the wxAMPS program indicate that for SiNx passivation on n-type silicon, the Fermi level shifts upward at low temperature such that the bottom of the SiNx/Si inversion layer lies below the Fermi level, resulting in the formation of two-dimensional electron gas (2DEG) detectable by EPR. This behavior does not occur in AlOy-passivated samples due to the opposite polarity of fixed charges in AlOy, including holes in Si wafer. In addition, EPR shows wide cyclotron resonance peaks near ~2000 G in SiNx-coated samples, attributed to electrons both in the Si bulk and in 2DEG. We further demonstrate that EPR signals from the bulk and the interface can be distinguished through angle-dependent measurements and excitation by light. This work establishes direct correlation between EPR signatures and surface passivation schemes in silicon photovoltaics and provides insights that may enable improved passivation strategies and facilitate future studies of low-temperature 2DEG behavior relevant to silicon-based microelectronic devices.
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