| The design of heterostructure devices that utilize the bandgaps and band offsets of different semiconductor materials is what is commonly referred to as "bandgap engineering." While these structures have been fabricated for some time, many questions regarding the fundamental aspects of heteroepitaxy still remain. The quality of surfaces and interfaces formed during III-V semiconductor heteroepitaxy can substantially affect device characteristics, making it a relevant and critical issue in the development of many modern devices. In this work, the fundamental issues that arise in semiconductor heteroepitaxy will be identified and addressed in two general categories. The first is lattice-mismatched growth, specifically, the growth of InAs on GaAs will be discussed. InAs growth on the GaAs(001) surface proceeds via the Stranski-Krastanov growth mechanism in which 3-D islands (islands larger than one monolayer in height) emerge after the formation of an In(Ga)As wetting layer. We compare experimental results with Monte Carlo simulations to characterize the initial stages of the wetting layer formation in which InAs islands initially form on the GaAs(001)-(2 x 4) surface. In contrast, for InAs growth on the GaAs(111)A surface, strain relaxation does not occur by surface roughening, but rather by the formation of misfit dislocations while maintaining a layer-by-layer growth mode. Surprisingly, it turns out that thin GaAs buffer layers can exhibit a "compliant" nature and affect strain relaxation. Accordingly, the dependence of strain relaxation on the thickness of the GaAs buffer layer has been investigated on the (111)A surface by measuring the changes in the in-plane lattice constant of the evolving InAs films. The second category is the lattice-"matched" growth of semiconductor heterostructures that contain both arsenides and antimonides, specifically, the growth of AlSb on InAs. When forming InSb-like interfacial bonds, the stoichiometry of the different reconstructions that appear during growth produces surface roughness. The surface topography of the AlSb films has also been studied using a variety of growth conditions and techniques. Several changes in the growth parameters have been implemented into resonant tunneling diodes and preliminary results will be discussed. |
