Prospects for atomically ordered device structures based on STM lithography

A new approach to future nanodevice fabrication is proposed which could, if successful, realize practical 3-dimensional control over electron transport in silicon and silicon-based heterostructures down to the atomic scale. The process we envision consists of:he following steps: (1) STM-induced desorption of hydrogen atoms to expose bare silicon dangling bonds on an H-terminated surface, (2) dosing with a few Langmuirs of PH3, AsH3, or B2H6 to deposit self-ordered arrays of dopant precursors onto the STM-exposed regions, (3) low-temperature silicon overgrowth using techniques designed to limit dopant redistribution to the atomic scale, (4) repetition to produce 3-dimensional electronic architectures. Reproducible electrical properties are made possible by the large Bohr diameter for bound state wavefunctions on the individual dopants, approximately 6.6 nm for electrons with in-plane mass m* = 0.190m(o), and preliminary calculations indicate that this same distance scale may apply to wave function coupling across lateral gaps between lithographically defined high-density donor/acceptor sheets. Potential advantages include: (1) elimination of disorder in random impurity doping, (2) greatly simplified all-UHV processing, (3) elimination of surface effects and offset charges through epitaxial encapsulation, (4) lateral tunnel junctions with reproducible impedance, and (5) structuring of electron transport in any desired 2D or 3D configuration. (C) 1998 Elsevier Science Ltd. All rights reserved.