RESEARCH INTERESTS

Experimental Condensed Matter

BIOGRAPHY
B.S., Physics (1980)
University of Peradeniya
M.S., Physics (1985)
University of Illinois at Chicago
Ph.D., Physics(1988)
University of Illinois at Chicago

The MicroPhysics Laboratory (MPL) pioneered the MBE growth, characterization, and device fabrication of HgCdTe and related materials for infrared focal plane arrays. As the Director of MicroPhysics Lab (MPL), my goal has been to form a major center for heteroexptiaxy with emphasis on the study of the physics of interface formation. With internal and external support, the MPL has already become such a center for researchers. I was able to increase our funding while several major research centers related to II-VI materials lost a majority of their funding. My ultimate organizational goal is to see the establishment of an interdepartmental, intercollegial Institute or Center for Materials Science and Technology with the emphasis in hetero-epitaxy. I have built research collaborations with national and international universities and institutes. I strongly believe that a close interaction between university and industrial researchers is not only important for moving forward the critical technologies, but also will provide appropriate training for graduate and undergraduate students. My personal research has centered upon the molecular beam epitaxial (MBE) growth of new heteroepitaxial systems under varied growth conditions, their characterization by electrical, structural and optical measurements, and the analysis of the results of these measurements to study the interfacial growth process. Semiconductor heteroepitaxy offers scientific and technological challenges because the two semiconductors on opposite sides of the heterointerface exhibit different lattice parameters, thermal expansion coefficients, and chemical bonding characteristics which can produce an electrostatic charge at the interface. These differences, and hence these challenges, are especially great for the growth of II-VI semiconductors on Si substrates, which have been pioneered by the MPL. The enormity of the difficulty of growing CdTe expitaxially on Si is obvious when one considers that (1) the lattice constants of CdTe and Si differ by 19.3 per cent, (2) the thermal expansion coefficients differ by almost a factor of two, and (3) CdTe has a large ionic component to its bonding, whereas Si bonds purely covalently. Usually, the accommodation of the lattice mismatch is achieved through interfacial dislocations, which are generated at the interface and propagate into the growing crystal. Yet, we have recently been able to reduce the dislocation density in CdTe/Si to 105 cm 2 , approximately the same density found in high quality bulk CdTe. This was achieved by introducing an interfacial layer, such as As, which has allowed the formation of coherent interface. The lattice mismatch was relaxed by almost perfect misfit dislocations. We were able to achieve this by careful understanding of the substrate surface and growth nucleation. MPL is currently focused on the issues related to the multicolor infrared detectors operated at high temperatures and direct localized epitaxial growth of HgCdTe/CdTe on processed Si with CMOS circuits (including the metallic interconnects). This will make it possible to fabricate monolithic large area infrared focal plane arrays. In addition, we have used our knowledge on the epitaxial growth of CdTe/Si to grow Ge on Si. Our initial results are encouraging. MPL will further expand its research focus to include SiGe, which has several novel device applications such as heterojunction bipolar transistors.

PUBLICATIONS

• Authored or co-authored over 170 refereed journal articles and oral presentations."Understanding ion-milling damage in Hg1-x CdxTe epilayers" C. Wang, D. Smith, S. Tobin, T. Parodos, J. Zhao, Y. Chang, S. Sivananthan. Journal of Vacuum Science Technol
• Performance and Reproducibility Enhancement of HgCdTe Molecular Beam Epitaxy Growth on CdZnTe Substrates Using Interfacial HgTe/CdTe Superlattice Layers. Y. Chang, J. Zhao, H. Abad, C.H. Grein, S. Sivananthan, T. Aoki, D. Smith, APL 86, 131924 (March
• Composition and thickness distribution of HgCdTe Molecular Beam Epitaxial Wafers by Infrared Microscope Mapping. Y. Chang, G. Badano, E. Jieang, J.W. Garland, J. Zhao, C.H. Grein, S. Sivananthan. Journal Crystal Growth Volume 277, issue 1-4 Page: 78 (2005
• "Growth of Tellurium on As-exposed Si(211): Electronic Structure Calculations". B. Gupta, I. Batra, S. Sivananthan, Physical Review B 71, 1 (2005)
• Formation Mechanism of Crater Defects on HgCdTe/CdZnTe (211)B Epilayers Grown by Molecular Beam Epitaxy, Y. Chang, G. Badano, J. Zhao, C. H. Grein, S. Sivananthan, T. Aoki, and David. J. Smith, Appl. Phys. Lett., 83(23), 4785(2003)