Le séminaire Extending GaAs-Based Planar Heterostructures to Longer Wavelengths se déroulera en anglais seulement.
Bienvenue à tous!
Dr. Patricia Mooney
Physics Department, Simon Fraser University
Extending GaAs-Based Planar Heterostructures to Longer Wavelengths
Semiconductor heterostructures, consisting of nanoscale epitaxial layers having different bandgap energies, are employed in a wide variety of applications including high efficiency multi-junction solar cells, lasers, and light emitting diodes. However, the change in bandgap energy with alloy composition is often accompanied by a change in the lattice constant of the material, for example, the alloy InxGa1-xAs. Therefore, above a critical layer thickness, relaxation of lattice mismatch strain through the introduction of 60⁰ misfit dislocations makes the structures unsuitable for their intended application. I will discuss two projects aimed at overcoming this limitation of planer semiconductor structures.
One project involves the fabrication of “engineered substrates” having a lattice constant at the wafer surface that is larger than the lattice constant of the Si or GaAs wafer. This is achieved by growing a compressively strained epitaxial SiGe/Si or InGaAs/GaAs layer structure on top of a sacrificial layer. Removing this layer by selective wet chemical etching allows the strained structure to expand elastically without misfit dislocations. A subsequent heat treatment forms covalent bonds between the strain-relaxed structure and the original substrate. The structural and electronic properties of bonded structures having lattice constants up to 5% larger than that of GaAs (equivalent to strain-relaxed InGaAs with In fraction ~8%) will be presented.
We are investigating a novel semiconductor alloy, GaAsBi, where the large reduction in bandgap energy as the Bi fraction is increased is accompanied by a relatively small increase in lattice constant. This alloy has interesting properties for opto-electronic devices. But epitaxial growth of GaAsBi films is difficult because Bi is incorporated into GaAs only at growth temperatures below 400⁰C, where high concentrations of point defects in the layers are expected. Using Deep Level Transient Spectroscopy (DLTS) we showed that incorporating Bi suppresses the dominant defect in n-type GaAs grown by molecular beam epitaxy (MBE) at 330⁰C, thus reducing the total defect concentration in GaAsBi by a factor of 20. The defects detected in n-type GaAsBi layers having Bi fraction up to 1.1% are As anti-site complexes, which are also present in comparable concentrations in GaAs layers grown at this temperature.
Patricia M. Mooney is Professor Emerita at Simon Fraser University, British Columbia, Canada. Prior to joining the SFU Physics Department as Tier 1 Canada Research Chair in Semiconductor Physics in 2005, she was a Research Staff Member at the IBM T.J. Watson Research Center, Yorktown Heights, NY for 25 years. Dr. Mooney is the author of more than 200 publications, including review articles, a monograph and several book chapters, and also has 18 issued patents. She received two outstanding Technical Achievement Awards from the IBM Corporation in addition to several patent awards.
Dr. Mooney is a Fellow of the Royal Society of Canada (RSC), the American Physical Society (APS), the American Association for the Advancement of Science (AAAS) and the Materials Research Society (MRS), and is a member of the Canadian Association of Physicists (CAP). She currently serves on the Interdisciplinary Adjucation Committee of the Canada Research Chairs Program. She recently served on the Governing Board of the American Institute of Physics, on the NSERC Grants Selection Committee for the Major Resources Program, and on the CAP Brockhouse Medal Award Committee. Previously she served on the APS Council, representing the Forum on Industrial and Applied Physics, and also on the APS Executive Board. She is Past Chair of the Division of Materials Physics (DMP) of the APS and has served on many APS Committees. She has been a member of the editorial boards of Physical Review B, Applied Physics Letters/Journal of Applied Physics and the Journal of Materials Science: Materials in Electronics. Dr. Mooney was chair of the Gordon Research Conference on Defects in Semiconductors, organized symposia at MRS meetings, and has served on the program committees of numerous other conferences. She was recently a member of the International Advisory Board of the International Conference on Defects in Semiconductors and currently serves on the Steering Committe for the International Workshop on Bismuth-Containing Semiconductors.
