Development and application of a III-V surface electron microscope
thesisposted on 17.02.2017 by Zheng, Changxi
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
GaAs based communication and optoelectronic devices are widely used in our daily lives. Applications range from mobile phones and satellite communications to laser pointers, printers, barcode readers and DVD players. The components making up these devices are composed of thin layers of III-V semiconductor material, the thicknesses of which must be finely controlled. This is achieved by growing such layers via molecular beam epitaxy (MBE) with atomic layer precision. In addition to current technologies, the long-term research objective in III-V materials is to utilise variants of MBE to fabricate new quantum structures of nanoscale dimensions for new device applications. However, despite this current and future technological importance, the real-space imaging of III-V MBE surface growth dynamics is restricted by the presence of large incident As flux which restricts the use of conventional imaging techniques. To address this issue, the main goal of this thesis is therefore to develop a unique surface electron microscope to study the surface dynamics of III-V materials in real-time during MBE growth. The thesis begins with the design and development of a III-V low energy electron microscope (LEEM). The incorporation of III-V MBE and a high As flux, in particular, required numerous modifications to a commercial LEEM instrument (Elmitec LEEM III). These are described in detail in Chapter 2. Following the development of the LEEM it is important to understand the contrast associated with quantum structure formation. With this in mind, theories of mirror electron microscopy (MEM) were developed and experimentally verified using Ga droplets and their associated surface trails as convenient test objects. This work resulted in the development of the Laplacian and caustic theories of MEM imaging which is fully described in Chapters 3, 4 and 5. Finally, based on the advances in instrumental development and imaging, proof-of-principle applications were undertaken to confirm that III-V and other materials could be investigated under high As flux. These included the control of the GaAs (001) congruent evaporation temperature by As flux (Chapter 6), the asymmetric coalescence of Ga droplets during Langmuir evaporation (Chapter 7), and the dynamic behaviour of As on Si(111) at high temperatures (Chapter 8).