Synthesis and Properties of GaAs1-xBix Prepared by Molecular Beam Epitaxy
GaAs1-xBix is a III-V semiconductor alloy which has generated much fundamental scientific interest. In addition, the alloy possesses numerous device-relevant beneficial characteristics. However, the synthesis of this material is very challenging and its properties are not well understood. The focus of this dissertation is to advance the understanding of its synthesis using molecular beam epitaxy (MBE) and, as a result, improve its key as-grown properties that are of great importance to device applications, such as increasing Bi concentration in the alloy and enhancing its optical emission efficiency. In chapter 3, the discovery of a trade-off between the structural and optical characteristics of GaAs1-xBix , controlled by the degree to which the growth is kinetically-limited, is described. Chapter 4 discusses the exploitation of a growth method that utilizes the spatial distribution of MBE fluxes to facilitate numerous studies of the critical dependence of GaAs1-xBix characteristics on the V/III flux ratio. Chapter 5 describes the results of experiments utilizing vicinal substrates to modify both Bi incorporation and optical emission efficiency of synthesized GaAs1-xBix and enable new understanding of the Bi incorporation mechanism. Specifically, incorporation primarily at A steps, defined as the steps generated by misorienting the GaAs (001) substrate toward the (111)A surfaces, enhances Bi incorporation but reduces optical emission efficiency. Chapter 6 describes the identification of two new signatures in the Raman spectra of GaAs1-xBix that can be used to determine the Bi content and the hole concentration of nominally undoped GaAs1-xBix. Finally, in Chapter 7 the GaAs1-xBix growth using pulsed Ga fluxes is described. The use of pulsed-growth significantly modifies the incorporation of Bi and suggests it is a promising method for widening the GaAs1-xBix MBE growth window enabling improved synthesis control and materials properties.
Electrical engineering, Materials Science, Physics, Dilute Bi, GaAsBi, molecular beam epitaxy, x-ray diffraction
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