Application of Focused Ion Beam for Micro-machining and Controlled Quantum Dot Formation on Patterned GaAs Substrate

Abstract
This project is a study based on the application of focused ion beam (FIB) instrumentation, which has been widely used in fields such as electronic engineering, materials science, semiconductor technology and nanotechnology. We used a Ga+ source focused ion beam column from Orsay Physics mounted on a JEOL 6500F scanning electron microscopy, which forms a SEM-FIB dual-beam instrument.
This project consists of a few experimental projects based on the applications of the FIB in electronic engineering. The experimental work will demonstrate the micro-machining capability of the FIB system. The projects include the TEM/STEM cross-sectional sample preparation and the fabrication of a ring shaped aperture and a coded aperture for (S)TEM imaging.
The major project is to study InAs quantum dots grown on a FIB patterned GaAs (100) substrate, in order to produce regular arrays of quantum dots at specific sites. In(Ga)As quantum dots have been a very popular topic in electronic engineering for a long time. InGaAs quantum dots have an energy band gap between 0.66eV and 1.41eV, covering the range from infrared (IR) to visible light, which can be used for constructing infrared detectors, solar cells and etc. Regular quantum dot arrays are expected to have better size distribution and high uniformity over a small area with respect to randomly located self-assembled quantum dots, which results in better opto-electronic performance. Overgrowth of a FIB patterned substrate is one of the techniques to produce regular quantum dot arrays. Island-shaped quantum dots are nucleated at specific locations where the ion beam has formerly patterned the surface. Different ion beam patterning parameters are compared and optimized, including accelerating voltage, probe current, dwell time, pitch, growth temperature and thickness of deposited InAs. We have determined the range of the ion beam parameters and the overgrowth conditions, which consistently produce regular quantum dot arrays at the patterned areas without nucleation outside the patterned areas. The relationship between the size of the formed islands and the patterning parameters is investigated by analysing SEM images and AFM images. Micro-photoluminescence and TEM EDX analysis are applied to study the islands formed, to find out the optoelectronic performance and the chemical composition.