Effect of energetic ion irradiation on CdI2 films

Abstract

The effect of energetic argon ion irradiation, using a 3.3 kJ pulsed plasma focus device, is studied systematically on a 4H polytype (002)-oriented CdI2 stoichiometric film having compressive residual stress. The CdI2 films were exposed to energetic ions from the plasma focus device at different distances from the top of the central electrode. The irradiation was found to change the orientation of the film to (110) at certain moderate irradiation distances. A linear decrease in grain size and residual stress was observed with decreasing irradiation distance (or increasing ion energy), consistent with both structural and morphological observations. The direct optical energy gap Eg was found to increase linearly at the rate 15 μeV/atm with the compressive stress. The combined data of present compressive stress and from earlier reported tensile stress show a consistent trend of Eg change with stress. The iodine–iodine distance in the unit cell could be responsible for the observed change in Eg with stress.