Effects of Bi on the Morphology and Atomic Structure of III-V Semiconductor Surfaces.

[摘要] Use of Bi in III-V semiconductor films in recent years has a variety of applications.Bi lowers the bandgap, introduces a large spin-orbit coupling, and preserves electronmobility, enabling low bandgap, high mobility and novel spintronic devices. Bi isalso a nearly ideal surfactant, smoothing the surface, creating the right conditionsfor a sharp, high quality interface. However, the mechanism for this behavior andthe atomic surface reconstructions are poorly characterized, both for surface- andbulk-incorporated Bi. This dissertation consists of four studies to investigate thisbehavior.The first half explores the effects of Bi as an ideal surfactant. The first studyis an experimental scanning tunneling microscopy characterization of the Bi/GaAssurface, revealing the same reconstruction appears for the observed (1x3), (2x3), and(4x3) reflective high-energy electron diffraction patterns. Steps become wider on themicron length scale from the induced smoothing, owing to the increase of oppositedirection step edges on the nanometer length scale. The second study is a combinedcluster expansion aand density functional theory (DFT) analysis of the Bi/GaAsxvireconstructions. The (4x3) reconstruction was found to stabilize into a variety ofcompositions in the presence of Bi. Monte Carlo analysis of the (4x3) reconstructionshows a strong propensity for surface disorder even at temperatures well below Bideposition temperatures.The second half focuses on the surface effects of incorporated Bi. In the thirdstudy, several GaSbBi films were grown as a function of Ga, Sb, and Bi growthrates. Biphasic droplets were observed, with sub-droplets, facets, and etching intothe film. X-ray diffraction and Rutherford backscatter measurements showed a con-current increase in Bi and As concentration, indicating a previously unseen strainauto-compensation mechanism. The fourth study is a cluster expansion/DFT char-acterization of the Bi/GaSb surface system as a proxy for the GaSbBi surface. In par-ticular, the c(2x10) reconstruction was investigated for the bare GaSb and Bi/GaSbsystems, where the instability of this reconstruction was established in a rigorousmanner. Finally, the Bi-induced (2x1) reconstruction was found to be stable in theBi/GaSb system, consistent with other Bi/III-V systems.

[发布机构] University of Michigan

[效力级别] Molecular Beam Epitaxy (MBE)

[关键词] Bi-induced III-V Semiconductor Surfaces;Molecular Beam Epitaxy (MBE);Density Functional Theory (DFT);Bi Surfactant on GaAs and GaSb;Bi Incorporation Into GaSb;Reconstruction Stability of Bi/GaAs and Bi/GaSb;Materials Science and Engineering;Engineering;Science;Materials Science and Engineering