A systematic investigation of structural and optical properties of Li ion implanted MgTiO3 thin films

Abstract

Effects of lithium (Li) ions implantation on structural, optical, and luminescent properties of MgTiO3 (MTO) thin films were investigated in the present report. The films were initially deposited at a substrate temperature of 200 °C, which were then annealed at 700 °C for crystallization. Crystalline MTO films were implanted with 30 keV Li ions at various fluences ranging from 1 × 1014 to 1 × 1015 ions/cm2. The crystallinity of films decreases upon Li ions implantation at a fluence of 1 × 1014 ions/cm2. In contrast, a further increase in fluence to 1 × 1015 ions/cm2 results in an improvement in crystallinity. Annealed and implanted films show lesser transmittance than the as-deposited films. As-deposited film exhibits a bandgap of 3.79 eV, which increases to 4.28 eV upon annealing the films. Subsequently, with an increase in implantation fluence, the shrinkage in optical bandgap from 4.26 to 4.09 eV is observed. Moreover, the annealed films exhibit a refractive index of ∼2.2 which is higher as compared to as-deposited and implanted MTO samples. X-ray photoelectron spectroscopy was carried out to investigate the surface states related to Mg, Ti, and O in the samples and to analyze the variation of defects’ concentration with implantation. MTO thin films show luminescent centres in near ultraviolet and visible region. The annealing results in the enhancement of photoluminescence intensity which decreases on implantation, and a drastic quenching of intensity was observed at a fluence of 1 × 1015 ions/cm2. The average decay lifetime of as-deposited film is 9.1 ns. Annealing results in an increase in the average decay lifetime, while implantation leads to the reduction of average decay lifetime of MTO films.