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 ($10\hspace{0.5em}\mathrm{nm}$). 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 $\Delta E_V$ with $C_{\mathrm{H}}$ by about $13\hspace{0.5em}\mathrm{meV}/\mathrm{at}.\mathrm{\hspace{0.5em}}\mathrm{\%}\mathrm{\hspace{0.5em}}\mathrm{H}$. The discrepancy with the $30-40\hspace{0.5em}\mathrm{meV}/\mathrm{at}.\mathrm{\hspace{0.5em}}\mathrm{\%}\mathrm{\hspace{0.5em}}\mathrm{H}$ 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.

• Received 22 December 2010

DOI:https://doi.org/10.1103/PhysRevB.83.165314