Gap state distribution of amorphous hydrogenated Si and Si:Ge alloys

Abstract

Measurements of transient photoconductivity (TPC), steady state photoconductivity (SPC), and the frequency dependence of the junction capacitance of Schottky diodes (C−ω) have been used to obtain the energy distribution of gap states in a-Si:H alloys before and after light soaking. It is found that light soaking gives rise to new gap states 0.35 eV to 0.65 eV below the conduction band mobility edge. TPC and C−ω measurements on a-Si:Ge:H alloys (40% Ge) show that addition of Ge also creates gap states in the same energy region. Space charge limited conduction (SCLC) has been investigated in sandwich structures of these materials. The gap state distribution derived from these measurements agrees with that obtained from TPC and SPC indicating that these co-planar electrode techniques measure the bulk DOS.