Solid State Physics, Physics of Semiconductor Quantum Structures
Ph.D. California Institute of Technology 1992; M.S. California Institute of Technology 1988; B. S. University of Arizona 1987. Honors and Awards: National Science Foundation Graduate Fellowship, 1987-1990; AT&T Ph.D. Scholarship 1990-1992.
The advent of non-equilibrium growth techniques which are capable of sub- nanometer compositional control has enabled materials physicists to produce artificially structured semiconductors with new physical properties. Superlattices, quantum wells, and resonant tunnelling structures exemplify the new class of nano-structured materials which has impacted science and technology in the last decade.
Peter Sercel's research is directed at extending the ability to structure materials with nanometer precision from one dimension, characteristic of conventional techniques such as molecular beam epitaxy (MBE), to three dimensions. This capability will enable experimental realization of quantum dots, model structures which behave as three dimensional quantum wells. The interaction of the electronic wavefunction with the boundary of such a structure causes the energy levels to be quantized; the energy level structure of a quantum dot is more akin to that of an atom than a bulk semiconductor. In particular, the optical transition oscillator strength is condensed in to a series of discrete lines. l Arrays of quantum dots embedded in a semiconductor matrix of larger band-gap thus represent an entirely new class of material characterized by extremely narrow linear absorption and gain spectra and enhanced optical non-linearities.
The challenge in this research is to develop an epitaxial growth technology which is capable of achieving nanometer-scale lateral structure definition. A novel approach to this problem being developed in Sercel's lab utilizes very-low-energy group-III metal cluster deposition to seed low temperature vapor-liquid-solid epitaxial growth of III-V quantum dots directly on a semiconductor substrate. Arrays of quantum dots produced in this way can then be "buried" by conventional MBE growth of a wider bandgap semiconductor such as AlxGa1-xAs producing the desired composite structure. These experiments will be performed in a custom built ultra high vacuum deposition chamber equipped with Knudsen type effusion cells, a custom cluster deposition source, and standard surface analysis tools. Ultimately, the technique may be combined with cluster mass filtering techniques to produce embedded fields of highly uniform quantum dots for applications to photonic devices such as the semiconductor laser.
A second experiment underway in Sercel's lab center around the production and characterization of free-standing quantum dots. Samples are grown by gas-phase homogeneous nucleation from a non-equilibrium vapor produced by explosive vaporization of a bulk semiconductor filament in an inert ambient. The quantum dots are collected thermophoretically on an appropriate substrate, permitting structural characterization by transmission electron microscopy and analysis by low temperature photoluminescence and absorption spectroscopy. The phenomenon of efficient visible photoluminescence from nanometer-scale silicon quantum dots produced in this manner is a current subject of investigation.