General Colloquium:
October 7 - 4:00pm Phys 223
(Coffee at 3:30p.m. in room 242)

Professor Eugene E. Haller
University of California at Berkeley
Dept. of Materials Science and Mineral Engineering
and
Lawrence Berkeley National Laboratory
Materials Sciences Division

Title: "Isotopically Controlled Semiconductors"

Abstract
The increase in the availability of highly enriched isotopes of numerous elements, including those forming semiconductors, has led to a sharp rise in the number of experimental and theoretical studies with isotopically controlled semiconductor crystals. In this talk I will review results obtained with isotopically pure as well as deliberately mixed semiconductor bulk crystals and thin film isotope heterostructures. Isotopic composition affects several properties of a semiconductor such as phonon energies, bandstructure and lattice constant in subtle but significant ways. Large isotope related effects are observed for thermal conductivity, local vibrational modes of impurities, after neutron transmutation doping (NTD) and for the lifetime of some electronic devices. Isotope heterostructures are especially well suited for self-diffusion studies. The absence of any chemical, mechanical or electrical driving forces makes possible the study of an ideal random walk problem. Recent results obtained with Si, Ge, GaAs, GaP and GaSb will be reviewed.

Major Research Areas

Awards and Fellowships
Recipient James C. McGroddy Prize for New Materials of the American Physical Society, 1999

Recipient Max-Planck Research Award, 1994

Research Professor, Miller Foundation for Basic Research in Science, 1990

Fellow, American Physical Society, 1986

U.S. Senior Scientist Award of the Alexander von Humboldt Foundation, 1986

More information on McGroddy Prize


Semiconductor crystal growth: Vapor phase epitaxy of wide bandgap GaN on sapphire and SiC; Liquid phase homo-epitaxy of ultra-pure GaAs on semi insulating and doped GaAs; Czochralski growth of ultra-pure and doped Ge crystal of natural and isotopically controlled composition; Semiconductor characterization: Electrical (variable temperature Hall effect and resistivity, Deep level transient spectroscopy (DLTS)), optical (far infrared spectroscopy with Fourier transform spectrometers, mid- and near-infrared, visible and ultraviolet grating spectrometers, photoluminescence) and ion beam characterization (Rutherford backscattering spectrometry RBS) of dopants, impurities, native defects and complexes in a number of semiconductor systems; Far infrared detectors and low temperature thermal sensors: Research and development of low background far infrared photoconductors and pyroelectric detectors for astrophysical, astronomical and cosmological applications; neutron transmutation doped Ge thermistors and thermistor arrays operating down to 10 milli Kelvin.