High Spatial Resolution Microanalysis of Semiconductor Interfaces

[摘要] The work presented in this thesis is concerned with high spatial resolution characterisation of compound semiconductor multilayer structures. The principal techniques used are high-angle annular dark field imaging (ADFI) and energy dispersive x-ray (EDX) microanalysis. These are both available on a scanning transmission electron microscope (STEM). The motivation for this project is that, to enable a greater understanding of material growth processes and of the electronic and optical properties of semiconductor multilayers, it is desirable to obtain a knowledge of the atomic perfection of, and elemental compositions across, layer interfaces in the materials. This thesis is primarily concerned with the analysis of AlGaAs/GaAs multilayer specimens grown by molecular beam epitaxy (MBE) and InGaAs/InP specimens grown by MBE and by atmospheric pressure metal-organic chemical vapour deposition (MOCVD). A brief description of the material growth processes and a general introduction to the structural and compositional characterisation of semiconductor multilayers is given in chapter 1. The theoretical bases that underlie the two analytical techniques used in this project are discussed in chapter 2. The chapter describes the way in which elastically scattered electrons can be used to provide compositional information on multilayers using the technique of high-angle ADFI. In preparation for the measurement of elemental compositions using EDX microanalysis, cross sections for the production of characteristic x-ray photons for the elements of interest in this project are calculated. Experimental procedures and data analysis techniques used in this thesis are established in chapters 3, 4 and 5. A detailed description of the STEM and its associated detectors is given in chapter 3. The discussion includes the calculation of the current density distribution in the electron probe used for each of the two analytical techniques. Chapter 3 concludes with a description of the technique used to prepare high quality cross-sectional specimens for microanalysis in a STEM. Considerations specific to the analysis of semiconductor multilayers using high-angle ADFI are addressed in chapter 4. Optimised experimental conditions for the technique are established, as is the image analysis technique that is used to yield as much information as possible from the acquired data. Chapter 4 also includes a description of a second composition sensitive imaging technique, namely structure factor contrast imaging which is principally used here for orienting the cross-sectional specimen in the microscope. Considerations relevant to EDX microanalysis of semiconductor multilayers are discussed in chapter 5. This includes a detailed description of a Monte Carlo simulation routine used to help in the interpretation of measured concentration distributions from interface regions. The application of EDX microanalysis and high-angle ADFI to the characterisation of the materials of interest is described in chapters 6, 7 and 8. In the study of high quality MBE grown AIGaAs/GaAs specimens described in chapter 6, emphasis is given to the development of a results analysis procedure that utilises the full potential of each analytical technique. The investigation of the InGaAs/InP specimens grown by atmospheric pressure MOCVD is described in chapter 7. In this chapter, the procedures developed in chapters 2 to 6 are used to provide as much information as possible on the variation in elemental composition across interfaces and at layer centres in the system. This information is used by material growers to modify and improve atmospheric pressure MOCVD growth techniques. Similar studies are carried out in chapter 8 in the investigation of MBE grown InGaAs/InP specimens. Finally, in chapter 9, general conclusions are drawn on the work described in this thesis and suggestions are made for future studies of semiconductor multilayers in a STEM.

[发布机构] University:University of Glasgow

[关键词] Condensed matter physics