Collaborative Research: Using Nanoscale Patterning to Reveal the Atomic-scale Effects which Drive Unstable Growth on GaAs (001)

University Of Toledo, Toledo OH

Investigators

Abstract

Technical: Lithographic patterning followed by epitaxial growth provides a viable candidate to achieve rapid fabrication of large arrays of nanometer scale structures. Recent research reveals a transient instability in molecular beam epitaxial (MBE) growth of GaAs(001) on patterned substrate surfaces. Structures whose lateral dimensions exceed a thickness-dependent critical value increase in height, while those smaller than this value decay. This project is to investigate the effects responsible for growth instabilities of GaAs(001) surfaces patterned at various lateral length scales. The research bridges the gap in the scale between micrometers, where a continuum description is valid, and nanometers, where atomic scale processes enter more directly into the evolution. The project uses an integrated experimental/theoretical approach. In experiments, electron beam lithography is used to produce groove structures of dimensions as small as a few 10's of nanometers on substrates, which are used to grow GaAs at controlled temperatures, growth rates and As2/Ga flux ratios. A combination of photo lithography and electron beam lithography is utilized to fabricate hybrid nanometer/micrometer structures. Kinetic Monte Carlo (KMC) calculations are to be carried out for comparison with observations of the evolution during growth on the smaller structures. The goal is to understand the physical significance of the coefficients of the terms in the continuum equation. A second, more ambitious theoretical goal is to find an equation which has the CKPZ form in the continuum limit, but with correction terms that manifest themselves at the atomic scale. The research adopts a multi-scale approach in determining the rate and energy parameters for use in the KMC calculations, taking advantage of the existence of accurate quantum molecular dynamics (ab initio) methods based on density functional theory (DFT) that can accurately predict these parameters. Non-technical: The project addresses basic research issues in a topical area of materials science with high technological relevance. It aims at achieving a predictive capability for directed self organization and roughness control at the surface of a model substrate, GaAs, for applications in electronic, optoelectronic and spintronic devices. Through this project, graduate and undergraduate students will receive training in an interdisciplinary field. The results from this research projects will be introduced into the curriculum of two undergraduate courses, including one for a newly created Interdisciplinary NanoScience and Technology Minor program at the University of Maryland.