Spectral Properties of GaS Nanoparticles Obtained by Laser Ablation

Abstract

Bulk single crystals of GaS were grown by Bridgman-Stockbarger method in an evacuated (10-6 Torr) quartz ampoules of optical quality. Nanoparticles of quasi 2-D GaS crystals were obtained by laser ablation (LA) technique (KrF Excimer laser at 248 nm (COHERENT COMPex 201), and characterized by: XRF, GDOES, SEM, TEM and UV-VIS absorption spectroscopy. Nanoparticles obtained for the first time were ablated by using of excimer KrF laser operated at f = 50 Hz with pulse duration τ = 4 ns and maximum energy 200 mJ. Obtained results are analyzed with respect to particle size. Absorption spectra of particles with diameter less than 18 nm turned out to be shifted in the blue range of spectra. Blue shift in the optical absorption spectra of GaS nanoparticles with decreasing the particle sizes was explained by presence of nanocrystals in the quantum size regime. These results are consistent with a perturbation of GaS band structure due to carrier confinement, resulting in a widening of the forbidden gap.