Browsing by Subject "GaAsBi"
- Results Per Page
- Sort Options
Item Open Access GaAsBi Synthesis: From Band Structure Modification to Nanostructure Formation(2017) Collar, Kristen N.Research and development bismides have proven bismides to be a promising field for material science with important applications in optoelectronics. However, the development of a complete description of the electrical and material properties of bismide ternaries is not comprehensive or straightforward. One of the main benefits of this ternary system is the opportunity for bandgap tuning, which opens doors to new applications. Tuning the bandgap is achieved by means of varying the composition; this allows access to a wider energy spectrum with particular applications in long wavelength emitters and detectors. In addition to bandgap tuning, Bi provides an opportunity to decrease lasing threshold currents, the temperature sensitivity and a major loss mechanism of today’s telecom lasers.
We propose to characterize the electronic and chemical structure of GaAsBi grown by molecular beam epitaxy. We probe the binding structure using x-ray photoelectron spectroscopy. This provides insights into the antisite incorporation of Bi and the reactivity of the surface. Furthermore, we use XPS to track the energy variation in the valence band with dilute Bi incorporation into GaAs. These insights provide valuable perspective into improving the predictability of bandgaps and of heterostructure band offsets for the realization of bismides in future electronics.
The stringent growth conditions required by GaAsBi and the surfactant properties of Bi provide a unique opportunity to study nanostructure formation and epitaxial growth control mechanisms. The GaAsBi epitaxial films under Ga-rich growth conditions self-catalyze Ga droplet seeds for Vapor-Liquid-Solid growth of embedded nanowires. We demonstrate a means to direct the nanowires unidirectionally along preferential crystallographic directions utilizing the step-flow growth mode. We mediated the step-flow growth by employing vicinal surfaces and Bi’s surfactant-like properties to enhance the properties of the step-flow growth mode. Semiconductor nanostructures are becoming a cornerstone of future optoelectronics and the work presented herein exploits the power of a bottom-up architecture to self-assemble aligned unidirectional planar nanowires.
Item Open Access Synthesis and Properties of GaAs1-xBix Prepared by Molecular Beam Epitaxy(2016) Li, JinchengGaAs1-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.