Theses and Dissertations from UMD

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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    TEMPERATURE DEPENDENCE OF THE GROWTH MODE DURING HOMOEPITAXY ON PATTERNED GALLIUM ARSENIDE (001); ATOMIC-SCALE MECHANISMS FOR UNSTABLE GROWTH.
    (2006-12-11) tadayyon-eslami, tabassom; Phaneuf, Raymond j; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    ABSTRACT Title of Document: TEMPERATURE DEPENDENCE OF THE GROWTH MODE DURING HOMOEPITAXY ON PATTERNED GALLIUM ARSENIDE (001); ATOMIC-SCALE MECHANISMS FOR UNSTABLE GROWTH. Tabassom Tadayyon-Eslami, Doctor of Philosophy, 2006 Directed By: Professor Raymond J. Phaneuf, Department of Materials Science and Engineering In this thesis we present an extensive investigation of instability in molecular beam epitaxial growth of GaAs(001) over a range of pattern periods, cell sizes, growth temperature and As2 flux. We find very good agreement with predictions of the continuum models of Sun, Guo and Grant [Phys. Rev. A 40, 6763(1989)] for the growth above ~540ºC and Lai and Das Sarma [Phys. Rev. Lett. 66, 2348 (1991)] for the growth below this temperature. Changing the growth temperature to lower than 540 ºC leads to the formation of ring-like protrusions in the [110] direction around pits patterned on the initial substrate, which are absent for growth at higher temperature. This change in growth mode occurs in the temperature range within in which both pre-roughening transition and surface reconstruction transition (β2(2x4) to c(4x4)) also occur. We rule out the possibility of preroughening and the change in surface reconstruction as the reason for this growth mode change, based on the As2 flux dependence of the growth mode transition temperature. Based on our atomic force microcopy characterization of the surface morphology during early the stage of growth, we propose a physically based model for the growth, which involves a competition between decreased adatom collection efficiency during growth on small terraces and a small anisotropic multiple step Ehrlich-Schwoebel barrier at the pit edge. This provides a physical basis for the nonlinear term in the continuum models proposed by Sun et. al., and Lai and Das Sarma, whose predictions qualitatively describe our experimental observations.
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    Evolution of Patterned Gallium Arsenide (001) surface subjected to Molecular Beam Epitaxy Growth
    (2004-05-14) Shah, Sonam Shantilal; Phaneuf, Raymond J; Material Science and Engineering
    We describe here a study of lateral length scale dependence of the transient evolution of surface corrugation during MBE growth of alternating layers of AlAs and GaAs with individual layer thickness of 50 nm (approximate configuration as used in the distributed Bragg reflectors of a VCSEL) or GaAs layers onto the patterned GaAs (001) substrates. By patterning the surface with arrays of cylindrical pits of varying diameter and spacing, we were able to study selectively the changes which occur as a function of lateral period over a range of corrugation amplitudes. The evolution in the surface morphology after various stages of growth was characterized in air with AFM. We show that there exists a critical length scale which separates regimes of amplification and decay of corrugation amplitude with further growth. We compare our observations with the predictions of existing continuum models.