Bandgap engineering of low-temperature CdS nanocrystalline prepared on Si(1 1 1) without post-thermal annealing

Abstract

This article reports a new attempt for the bandgap formation of cadmium sulfide nanocrystals (CdS NCs) synthesized on Si(1 1 1) substrates at low temperatures: 50 and 150 °C. The influence of energy gap alteration on the optoelectronic properties was extensively considered with the aid of various tools. A wurtzite-–hexagonal structure in both CdS/Si NCs samples was confirmed by X-ray diffraction measurements. For a crystallite size around 7 nm, wider energy gaps (2.94–2.98 eV) were revealed by photoluminescence spectra. These values are in good conformity with the precise energy gaps, 2.95 eV and 3.04 eV which were estimated using a reflection-electron energy loss spectroscopy. Consequently, such expansion in the energy bandgap indicates the occurrence of a blue shift compared to the bulk CdS. Moreover, the Raman spectra show three peaks referring to the first-, second-, and third-order scattering of the longitudinal optical phonon modes. The findings demonstrate the improved crystalline quality of the sample prepared at 150 °C with no need for further thermal annealing. It is thus inferred that quantum confinement is possible in the CdS NCs prepared at low temperatures using a pulsed-laser deposition technique; thereby, they are useful for optoelectronic applications.