Colloidal synthesis and doping of semiconductor nanocrystals

Abstract

Colloidal semiconductor nanocrystals have drawn great interest for application areas in photonics and optoelectronics thanks to their superior optical properties including strong bandgap emission and tunability. Also, their suitability for solution-based processing has made them highly attractive for low-cost production of light-emitting diodes and lasers. Our objective in this thesis is to show the potential and versatility of semiconductor nanocrystals via colloidal synthesis and post-processing methods. The thesis work includes the synthesis of colloidal quantum dot and well structures and their post-doping and investigates their exciton decay dynamics. In this thesis a novel colloidal approach for the doping of zinc blende colloidal quantum wells was proposed and demonstrated for the first time. This new doping method uniquely relies on atomic layer deposition (ALD) process. Here we achieved the worlds first manganese-doped CdSe@CdS core@shell nanoplatelets using our technique of ALD-assisted doping. Also, we studied silver-doped CdTe quantum dots under different conditions. Our experimental work proved that the quantum yield enhancement of silver-doped CdTe quantum dots is a strong function of the nanocrystal size and doping concentration. Tuning the nanocrystal size and doping level, our aqueous core-only CdTe nanocrystals reached a record high photoluminescence quantum efficiency of 68%. For these quantum dots, various decay kinetics were proposed and the enhancement in the quantum yield was attributed to the trap state annihilation. The methods and results provided in this thesis contribute to the fundamental understanding of semiconductornanocrystals and pave the way for high-performance colloidal platforms and devices.