Electronic effects of ion damage in hydrogenated amorphous silicon alloys

Abstract

Electronic properties of silicon rich amorphous silicon alloys were investigated using diode structures and thin films on Corning 7059 glass following the implantation of 1 MeV Ge+ ions with doses up to 2.4×1015 ions/cm2. Optical absorption measurements on hydrogenated amorphous silicon (a-Si:H) and amorphous silicon nitride (a-SiNx:H) showed that the optical band gap decreases with the implanted ion dose. The hydrogen concentration was not affected by the implantation and therefore the change in optical band gap was consistent with a broadening of the band tails as confirmed by dual beam photoconductivity measurements. Annealing studies showed that recovery of the band gap could be achieved at temperatures of ≈250 °C. This recovery was almost complete following low dose ion implantation, but a residual amount of damage remained which increased with the dose before saturating. Results of electrical measurements on metal-semiconductor barriers showed a correlation between optical and electrical behavior with ion dose. We propose a model in which the barrier height and the optical band gap vary in the same way with the ion dose.