Band lineup in amorphous/crystalline silicon heterojunctions and the impact of hydrogen microstructure and topological disorder

Abstract

We determine the band offsets in amorphous/crystalline silicon [a-Si:H/c-Si{111}] heterojunctions using combined data from photoelectron spectroscopy and surface photovoltage measurements on structures comprising a-Si:H layers with device-relevant thickness ($10 \mathrm{nm}$). Altering the a-Si:H hydrogen (H) content ${C}_{\mathrm{H}}$ by the choice of deposition conditions, we observe a systematic retreat of the a-Si:H valence band edge leading to an increase of the band gap and the valence band offset $\ensuremath{\Delta}{E}_{V}$ with ${C}_{\mathrm{H}}$ by about $13 \mathrm{meV}/\mathrm{at}.\mathrm{ }\mathrm{%}\mathrm{ }\mathrm{H}$. The discrepancy with the $30\ensuremath{-}40 \mathrm{meV}/\mathrm{at}.\mathrm{ }\mathrm{%}\mathrm{ }\mathrm{H}$ predicted by theory can be consistently explained by the compensating effect of enhanced topological disorder imposed by the increasing density of microvoids as revealed by an analysis of the H microstructure. Thus we highlight the necessity of explicitly including the details of the H configuration in a theoretical treatment of the a-Si:H/c-Si heterojunction.