ELECTRONIC EFFECTS OF ION DAMAGE IN HYDROGENATED AMORPHOUS-SILICON ALLOYS

Electronic properties of silicon rich amorphous silicon alloys were in vestigated using diode structures and thin films on Coming 7059 glass following the implantation of 1 MeV Ge+ ions with doses up to 2.4 x 10 (15) ions/cm(2). Optical absorption measurements on hydrogenated amorp hous silicon (a-Si:H) and amorphous silicon nitride (a-SiNx:H) showed that the optical band gap decreases with the implanted ion dose. The h ydrogen concentration was not affected by the implantation and therefo re the change in optical band gap was consistent with a broadening of the band tails as confirmed by dual beam photoconductivity measurement s. Annealing studies showed that recovery of the band gap could be ach ieved at temperatures of approximate to 250 degrees C. This recovery w as almost complete following low dose ion implantation, but a residual amount of damage remained which increased with the dose before satura ting. Results of electrical measurements on metal-semiconductor barrie rs showed a correlation between optical and electrical behavior with i on dose. We propose a model in which the barrier height and the optica l band gap vary in the same way with the ion dose. (C) 1997 American I nstitute of Physics.