Improvement in the electrical properties of Se- and S-doped hydrogenated amorphous silicon thin films by annealing

Abstract

We studied the effect of annealing on the dark and photo conductivity of Se- and S-doped hydrogenated amorphous silicon (a-Si:H) thin films. The films were prepared on corning glass by using conventional plasma-enhanced chemical vapor deposition (PE-CVD). The samples were subsequently annealed in a vacuum (1 x 10(-6)Torr) at an annealing temperature of 300 A degrees C for an hour. The conductivity was measured in the temperature range of 300-470 K, which exhibited two different transport mechanisms. In the high-temperature range (370-470 K), the conduction was found to be an activated type while in the low-temperature range (less than 370 K), it was observed to follow variable range hopping. Arrhenius plots of the conductivities for S- and Se-doped a-Si:H films revealed that the activation energy was lower after annealing, owing to the removal of the surface defects created during deposition. The characteristic energy, E (MN), was lower in the annealed films for both types of dopant concentrations, which suggests a reduction in the number of traps. The photoconductivity was increased by vacuum annealing at 300 A degrees C by a factor of more than 10.