Conductive atomic force microscopy study of single semiconductor quantum dots and quantum dot aggregates.

摘要

The design, synthesis and characterization of nanoparticles are being actively studied in the last few decades since the size of features in modern technological devices become increasingly smaller. Semiconductor nanoparticles, often referred as "quantum dots" are playing an increasingly important role in material design and device fabrication. The electronic properties of the quantum dots aroused great interest for the last two decades. It has been proved that quantum dots have very different opti-electronic properties from the macroscopic semiconductors. Optical and electrical spectroscopies have been used to study the electronic properties of quantum dots but they all have their limitations. For example, they can only study ensemble properties and some of the transitions in optical spectroscopy are forbidden due to selection rules.;In this thesis, we provide a new way of using conductive atomic force microscopy to investigate the electronic properties of the quantum dots. In chapter 1, we give a brief introduction on semiconductors and quantum dots and review some theories used to describe the electronic properties and density of states in both bulk semiconductors and semiconductor nanocrystals. A description of scanning tunneling microscopy is introduced followed by a detailed discussion of how it can be used to study the quantum dots. Some basic theories are introduced and we will show some simulation results.;In chapter 3, we studied the size-dependent tunneling spectra of InSb quantum dots. We discovered significant difference in the local density of state between InSb and InAs quantum dots and the tunneling through L-point states in InSb quantum dots is discussed in detail with both experimental evidences and theoretical results. In chapter 4, we further discussed the quantum coupling effect between the InSb quantum dots. Chapter 5 is a detailed discussion of PbSe quantum dots, which is a shell-tunneling regime that is very different from the tunneling condition of InSb quantum dots.;With the knowledge of how to use tunneling microscopy to study the electronic properties of semiconductor nanoparticles, we have a new and powerful weapon dealing with these new materials. Understanding the electronic properties will help us greatly in designing and assembling new materials with new, controllable properties for use in electronic, optoelectronic, thermoelectric and photovoltaic applications.