Synthesis and characterization of In1-xGaxP colloidal quantum dots

Abstract

Colloidal quantum dots (CQDs) are semiconductor nanoparticles which have unique size and shape dependent optical properties. Because of these unique properties, CQDs have received considerable attention for fundamental interest and application to optoelectronic devices. These unique properties come from ‘quantum confinement effect’ and they give possibility to be used for light emitting diode (LED), solar cell, photo-detector, and bio-imaging agents. Early research projects focused only on group II-VI CQDs which contain lead and cadmium. Although group II-VI CQDs give high quality of optical properties and stability, because of the Restriction of Hazardous Substances (RoHS) from European Union, it is hard to commercialize group II-VI CQDs. To avoid RoHS, CQDs research actively has been performed to develop non-toxic CQDs which do not contain lead and cadmium such as InP, InAs, ZnSe and CuInS2. However most of the non-toxic CQDs research is focused on InP and CuInS2. Recently, research is underway to try to find new type of non-toxic CQDs such as GaP. In this dissertation, there are two subjects about colloidal quantum dots and its application. First subject is ‘Synthesis of InP colloidal quantum dots with white phosphorus for new phosphine precursor’. Most of the InP colloidal quantum dots are synthesized with tris(trimethylsilyl)phosphine [(TMS)3P] which gives monodisperse and highly crystalline InP CQDs. Although (TMS)3P gives high quality of InP CQDs, it is expensive and a pyrophoric material which produces PH3 and a highly toxic gas. In order to replace (TMS)3P, cheaper and safer phosphine precursors are studied such as aminophosphine, white phosphorus and so on. In this subject, InP CQDs are synthesized with white phosphorus via both hot-injection and heat-up method, which has great advantages to mass-scale production. Second subject is ‘Synthesis of In1-xGaxP alloy colloidal quantum dots and its optical properties.’ Although In1-xGaxP CQDs are already reported, the effect of indium/gallium ratio to optical properties is not examined well. In this subject, In1-xGaxP/ZnS (0 ≤ x ≤ 1) core shell CQDs were synthesized with different In/Ga ratio. The resulting In1-xGaxP/ZnS alloy CQDs were characterized by X-ray diffraction (XRD) pattern, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-mass spectrometry (ICP-MS), UV-Vis absorbance spectroscopy, photoluminescence (PL) spectroscopy, temperature dependent photoluminescence (TDPL) and so on.