Determination of the mobility gap of microcrystalline silicon and of the band discontinuities at the amorphous/microcrystalline silicon interface using in situ Kelvin probe technique

A method to determine the mobility gap of thin films and the band discontinuities in heterojunctions is presented. It combines in situ contact potential measurements with dark conductivity activation energy measurements. The method is applied to determine the mobility gap of microcrystalline silicon $\mathrm{(\mu c-}\mathrm{Si:H})$ and the band discontinuities at the $\mathrm{\mu c-}\mathrm{Si:H}$ /amorphous silicon $\mathrm{(a-}\mathrm{Si:H})$ interface. The mobility gap of $\mathrm{\mu c-}\mathrm{Si:H}$ depends on its crystalline volume fraction and varies between 1.48 and 1.55 eV. The main band discontinuity occurs at the valence band side. The consequences of the band discontinuities on $\mathrm{a-}\mathrm{Si:H}$ based solar cells using $\mathrm{\mu c-}\mathrm{Si:H}$ doped layers are discussed.