Electronic Structure of Some Zincblende Semiconductor Surfaces
The main aim of this thesis is to study and understand the surface electronic structure of compound semiconductors (ex. GaAs, InP, ..etc.) using both experiment and theory. The experimental technique is photoelectron spectroscopy, in particular the angle-resolved form, while theory uses the empirical tight binding (ETB) method with the Green's function forma-lism. Most of the thesis is devoted to the study of (110) surfaces. This surface is the natural cleavage plane for zincblende semiconductor compounds and is thus relatively easy to prepare for experimental work. The surface does not reconstruct, rather relax keeping the symmetry of the ideally terminated bulk, which makes calculations easier. If empirical calc-ulat-ions are performed in conjunction with experiments, evaluation of both can be improved.
In addition to clean surfaces, adsorbates are considered. In some cases the adsorbates are used as surface perturbation, in order to preferentially modify the surface states. Cs was used for this purpose to identify surface states which closely track bulk bands on CdTe(110).
Other adsorbate systems studied were As/GaAs(110) and As/InP(110). In these cases the adsorbate forms ordered overlayers. In the case of As/GaAs(110) the interaction between the As overlayer and GaAs substrate was found to be very weak and the overlayer desorbs if the temperature is around 100°C. In contrast, the interaction in the case of As/InP(110) was found to be strong, and around 330°C As-P exchange occurs in the first surface layer.
A different study, a tilted superlattice (TSL), is also included in this thesis. A tilted (GaAs)0.5(AlAs)0.5 superlattice was grown using molecular beam epitaxy (MBE) on a GaAs(100) substrate which resulted in GaAs and AlAs layers of 40 Å thickness each. The system was argued to be more suitable for studying interface properties by photoemission than conventional thin overlayer structures, for example to determine band offsets in heteros-tructures. Similar valence bands offset values of 0.4 eV were derived from valence and core-level spectra.