Hydrogen-terminated Silicon Surface Devices


Future Research Directions



Our development of high quality electron systems on silicon surfaces opens the door to several possible avenues of experimentation:

· High mobility electron and hole systems.  The H terminated surface can in principle be entirely free of imperfections (there is no intrinsic randomness or alloy disorder).  Can mobilities consequently approach those in the material systems created with molecular beam epitaxy?

· Interacting electrons on H:Si[111] surfaces.  The combination of the large valley degeneracy, the high effective mass, and the low effective dielectric constant all mean that interaction effects will be extremely important in H:Si[111] 2D electrons.  At the very least novel fractional quantum Hall effect (FQHE) phenomena should be observable in systems of sufficient mobility.  Also interesting are longstanding predictions of superconductivity in Si[111] 2D electrons and the possible relevance of valley degenerate FQHE states to topological quantum computing.

· 2D electron systems coupled to atoms or molecules attached or adhering to surfaces.  Electronic devices can shrink no further than to the scale of atoms and molecules, and most quantum dots and wires in semiconductors have  considerably larger than atomic dimensions.  Typically, high mobility electron systems must be buried deep within a semiconductor and cannot interact with small features on a surface.  The proximity of electrons to the surface in our devices means that coupling atoms and molecules to a 2D electron system will be possible, especially since chemists are developing new methods of linking molecules to a silicon surface.

· 2D nuclear-electron systems The surface hydrogen in our devices comprises a 2D nuclear spin system (I=1/2).  These nuclei may have a measurable effect on the electrons in the QHE regime.  The electron system in turn can be used to control nuclear interactions.  It is possible that such a system may facilitate new approaches to spin-based quantum information processing.

· Vacuum dielectric FETs.  While the trend in industry is to move towards high k dielectrics, there are reasons that physicists should be exploring the opposite limit.  A particular reason relevant to the future of quantum computing is that qubits always work best when they are cold, but the control electronics (which are ideally located near the qubits) will generate an increasing amount of heat as the number of qubits increases.  Vacuum gaps between the qubits and the control electronics may be necessary for the operation of truly large quantum computers.

· Donor qubit imaging and measurement using scanned probes.  Because of the near absence of surface states, H-terminated Si surfaces may be a nearly ideal “window” for probing donors beneath a silicon surface.  We are exploring using a scanned probe capable of resolving the force from single electrons, both to locate donors and to measure the dynamics of simple one and two electron systems coupled to Si donors.


To contact us:

Laboratory for Physical Sciences
8050 Greenmead Dr.
College Park, MD  20740
Lab Phone: 301-935-6415
Reception: 301-935-6400
Facsimile: 301-935-6723