Synthesis and characterization of Indium doped Lead chalcogenides(PbSe)100−xInx thin films composed of QDs

Abstract

As-prepared samples of (PbSe)100−xInx(x = 0, 5, 10 and 20) have been synthesized by melt-quenching method and their thin films have been deposited onto glass substrates(at 150 K) by thermal evaporation method. The structural studies of as-deposited thin films have been carried by using HRTEM, HRSEM and XRD analysis. These studies suggest that as-deposited thin films composed of aggregated cubic QDs and polycrystalline structure of the samples. The estimated size of the particles as suggested by the SEM images is found nearly consistent with that of most probable size (6–8 nm for 40% of QDs) as suggested by the TEM-histogram analysis. Due to induced-strain in the lattice, the particles' size is found reducing with increase in In content, this trend is verified by HRSEM images and full width half maxima values of XRD peaks. The QDs of the samples have been excited at wavelength of 300 nm and PL-emission peak has been observed at 370 nm. Blue shift and peak broadening effects are observed with increase in In content. These are the indications of quantum size effect and wide size distribution of the particles with increase in dopent concentration. Optical absorptions(200–900 nm) at room temperature, suggest a direct bandgap that increases with increase in doping content. This is the indication of the presence of defect states and high density of localized states. Width of the urbach tails in the localized states shows a narrowing trend with increase in doping content. This may be due to decrease in band tails which results in widening of optical band gap.