Determination of density of localized states in amorphous silicon alloys from the low field conductance of thin n-i-n diodes

Abstract

We describe a new technique to determine the density of localized states in the energy gap of amorphous silicon alloys from the temperature dependence of the low field conductance of n-i-n diodes. This new technique allows us to determine the bulk density of states in the center of a device. It involves fewer assumptions than other established techniques, and by varying the intrinsic layer thickness the density of states within approximately 400 meV of midgap can be determined. We measured the temperature dependence of the low field conductance of amorphous silicon alloy n-i-n diodes with intrinsic layer thicknesses of 0.55, 0.45, and 0.15 μm and deduced the density of localized states to be approximately 5×1016 cm−3 eV−1 at 0.45 eV and 5×1017 cm−3 eV−1 at 0.24 eV below the bottom of the conduction band.