Effect of Plasma Irradiation on $Cd I_2$ films

TL;DR

This study investigates how plasma irradiation affects the structural, morphological, and optical properties of CdI2 films, revealing orientation changes, grain size reduction, and a stress-dependent increase in the optical energy gap.

Contribution

It provides a systematic analysis of plasma irradiation effects on CdI2 films, highlighting the relationship between stress, orientation, grain size, and optical properties.

Findings

Orientation changes from (002) to (110) at certain irradiation distances

Grain size and residual stress decrease linearly with irradiation

Optical energy gap increases with compressive stress

Abstract

The effect of plasma irradiation is studied systematically on a 4H polytype (002) oriented ${\rm CdI_2}$ stoichiometric film having compressive residual stress. Plasma irradiation was found to change the orientation to (110) of the film 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 ${\rm E_g}$ was found to increase linearly at the rate ${\rm 15\mu eV/atm}$ with the compressive stress. The combined data of present compressive stress and from earlier reported tensile stress show a consistent trend of ${\rm E_g}$ change with stress. The iodine-iodine distance in the unit cell could be responsible for the observed change in ${\rm E_g}$ with stress.