Influence of Li ion implantation on LO phonon broadening and bandgap opening in ZnO thin films

Doping of nonmagnetic impurities in technologically important ZnO has opened a new window for achieving room temperature ferromagnetism, p-type carrier conduction, and enhancement of ferroelectric properties. Here, we report on the confined optical phonon and bandgap engineering in highly oriented Li implanted ZnO thin films. Using resonance Raman scattering condition, the confined longitudinal optical phonon lineshapes in uniaxial hexagonal wurtzite crystal are analyzed in detail using the phonon confinement model. We have demonstrated that phonon confinement model can yield a meaningful result for the interpretation of resonance Raman lineshapes if one considers the contribution of both the E1 (LO) and A1 (LO) modes, particularly while dealing with oriented ZnO thin films. Furthermore, with the increase in Li dose, the bandgap of ZnO is found to show a blue shift, and such blue shift in bandgap is explained using first principles calculation. •Pulsed laser deposited highly oriented ZnO thin films are implanted with low energy Li ions of different dose.•With the increase in Li concentration, the bandgap of ZnO is found to show a blue shift.•The blue shifting of the bandgap is explained using first principles calculation.•The phenomenological Phonon confinement model is used to explain the line shape of the Raman spectra under resonant conditions.