Semiconductor devices based on III-V materials have been the focus of intense research due to their superior electron mobility and favorable energy direct bandgap which are applicable in infrared wavelength range optoelectronics and high speed electronic systems. The thesis presented here consists of two thrusts; the first focusing on infrared applications, and the second focusing on InP-based heterojunction bipolar transistors (HBTs). In the first thrust, we investigate type-II InAs/GaSb superlattice IR detector devices and the effect of substrate orientation on InSb and InAs nanostructure morphology. In the second thrust, we study InP-based high frequency HBTs. A low resistance InAs ohmic contact is demonstrated, and we presented along with a study of the crystalline qualities in GaAs0.5Sb0.5 films grown on tilted- axis InP substrates. Chapter 2 presents fabrication and characterization of two type-II superlattice structures with 15 monolayer (ML) InAs/12ML GaSb and 17ML InAs/7ML GaSb grown on GaSb (100) substrates by solid-source molecular beam epitaxy (MBE). The X-ray diffraction (XRD) measurements of both the 15ML InAs/12ML GaSb and 17MLInAs/7ML GaSb superlattices indicated excellent material and interface qualities. The cutoff wavelengths of 15ML InAs/12ML GaSb and 17ML InAs/7ML GaSb superlattices photodetectors were measured to be 6.6μm and 10.2μm, respectively. These different spectral ranges were achieved by growing alternating layers of varying thicknesses which allowed for bandgap engineering of the superlattices of InAs and GaSb. Lastly, a mid-IR type-II superlattice photodiode was demonstrated at 80K with a cutoff wavelength at 6.6µm. The device exhibited a near background limited performance (BLIP) detectivity at 80K and higher temperature operation up to 280K. In Chapter 3, we show that the (411) orientation, though not a naturally occurring surface, is a favorable orientation to develop a buffer layer into a super flat surface at a certain high growth temperature. The (411) surface is a combination of localized (311) and (511) surfaces but at a high growth temperature, adatoms can obtain enough energy to overcome the energy barrier between these localized (311) and (511) surfaces and form a uniform (411) surface with potential minima. This results in a super flat surface which is promising for high-density nanostructure growth. In this work, this is the first time that the highest InSb and InAs nanostructures density can be achieved on the (411) surface which is in comparison with the (100), (311), and (511) surfaces. Chapter 4 of this thesis addresses the use of an InAs layer as a low-resistance ohmic contact to InP-based heterostructure devices. Selective area crystal growth of InAs on a dielectric (Benzocyclobutene, BCB polymer) covered InP (100) substrate and direct growth of InAs on InP substrate were performed by MBE. Heavy doping of InAs using Te was carried out to determine the lowest sheet resistance. Based on scanning electron microscope (SEM) and XRD measurements, increasing substrate temperature from 210 ℃ to 350 ℃, led to an improvement in crystallinity from a polycrystalline layer to a single crystal layer with a corresponding improvement of surface morphology. Moreover, a narrow X-ray diffraction peak indicated full-relaxation of the inherent 3.3% lattice-mismatch in InAs/InP layers. Furthermore, around 290 ℃ a tradeoff was reached between crystallinity and optimized dopant incorporation of Te into InAs for the lowest sheet resistance. Lastly, Chapter 5 discusses the effect of substrate tilting on the material properties of MBE grown GaAsSb alloys closely lattice-matched to an InP substrate. InP(100) substrates tilted 0°off-(on-axis), 2°off-, 3°off-, and 4°off-axis were used for MBE growth; then the material qualities of GaAsSb epitaxial layers were compared using various techniques, including high resolution XRD, photoluminescence (PL) and transmission-line measurements (TLM). Substrate tilting improved the crystalline quality of the GaAsSb alloys, as shown by a narrower XRD linewidth and enhanced optical quality as evidenced by a strong PL peak. The results of TLM show that the lowest sheet resistance was achieved at a 2° off-axis tilt.

The development and characterization of lithographically patterned dielectric superlattice systems are presented, which have enabled the first clear realization of fully developed fractal mini-gaps owing to the interplay between a quantizing magnetic field and a lithographically defined spatial superlattice potential. Following a history of lateral superlattice gating on 2-D electron gas systems, we present patterned dielectric superlattice graphene systems of unmatched quality, allowing for the characterization of Hofstadter fractal band structure under triangular and square lattice geometries. Hexagonal boron nitride, graphene heterostructures are uniquely suited to integration with patterned gating structures, due to their high mobility and thin encapsulating dielectric environment. These systems have already been utilized for the observation of Hofstadter’s fractal spectrum through the moiré superlattice effect, but such systems are limited in their tunability. The patterned dielectric superlattice allows for control of the superlattice geometry, polarity, and strength. Utilizing this control, we compare the resultant fractal spectra from both triangular and square superlattice potentials, which confer unique gap structures in agreement with their lattice symmetry. More generally, patterned dielectric superlattices can be used to generate a variety of spatially dependent scalar potentials onto van der Waals heterostructures with length scales of order 10nm, while maintaining low disorder.

Electron transport and relaxation may be substantially different in low-dimensional systems compared to that observed in bulk material. In the present work, Monte Carlo models are used for the solution to the Boltzmann transport equation, with scattering rates calculated quantum mechanically for superlattice and quantum wells. Carrier relaxation following optical excitation is examined in multiple quantum well systems. Simulated results of the carrier relaxation process in coupled asymmetric wells and modulation doped wells are in good agreement with published experimental results on similar structures. Scattering rates in superlattices due to polar optical phonons, intervalley phonons, ionized impurities and carrier-carrier scattering are derived. Carrier transport through high energy superlattice minibands is examined in superlattice base hot electron transistors. Additionally, transport in the ballistic limit in periodic quantum wire structures, including geometric superlattices, is examined utilizing a mode matching method. / Graduation date: 1992

Thesis (Ph. D.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains x, 73 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 69-72).

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Thesis (Ph. D.)--University of Oregon, 2007. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 209-231). Also available for download via the World Wide Web; free to University of Oregon users.

Thesis (doctoral)--University of Oulu, 2008. / Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph. D.)--University of Oregon, 2004. / On t.p. "m̲" and "n̲" are subscript. Typescript. Includes vita and abstract. Includes bibliographical references (leaves 147-153). Also available for download via the World Wide Web; free to University of Oregon users.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2002. / Includes bibliographical references (leaves 35-37). Also available in electronic version. Access restricted to campus users.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 179-190). Also available on the Internet.