Title :

Semimetal/Semiconductor Nanostructured Composites and Their Applications

Speaker :

Dr. Hong LU

Project Scientist

University of California, Santa Barbara (UCSB), USA

Venue :

Room 215, William M. W. Mong Engineering Building, CUHK

Date :

Nov 6, 2012, Tuesday
4:00 PM - 5:00 PM

Abstract :

Rare earth element Er has been shown to form Er-V nanostructures spontaneously when it is included in III-V semiconductor growth (note 1). The common group V elements in the Er-V/III-V composite materials form a continuous sub-lattice that provides a unique coherent single crystal with embedded nanostructures. Grown by molecular beam epitaxy (MBE), these composites with Er-V nanostructures, mostly nanoparticles, have shown very interesting electrical, thermal, mechanical, and magnetic properties. For example, the ErAs or ErSb nanoparticles in their corresponding III-V semiconductor matrix can behave like traps to yield ultrafast photo induced carrier lifetime for THz technology; submonolayer deposition of ErAs at the junction greatly enhances the tunneling current for multi-junction solar cells, and the Er-V nanoparticles also can behave like scattering centers and carrier donors which can lower the thermal conductivity and increase the electrical conductivity of the composites at the same time for thermoelectric applications (note 2). Due to the semi-metallic property of Er-V compounds, strong surface plasma resonance are observed within the bandgap of the III-V seminconductors as well as strong polarization-dependent absorption due to the shape of the Er-V nanostructures. These interesting optical properties of the nanocomposites open up new opportunities for this material into applications that cover a wide wavelength range from near infrared to THz. In the talk, I will demonstrate that by controlling the MBE growth process we are able to control the formation, size and shape of Er-V nanostructures, therefore we can engineer the properties of these semimetal-semiconductor nanocomposites for various applications.

Notes: 1. Dmitri O. Klenov, Daniel C. Driscoll, Arthur C. Gossard, and Susanne Stemmer, “Scanning transmission electron microscopy of ErAs nanoparticles embedded in epitaxial In0.53Ga0.47As layers”, Applied Physics Letters, 86, 111912 (2005).

2. Hong Lu, Peter G. Burke, Arthur C. Gossard, Gehong Zeng, Ashok T. Ramu, Je-Hyeong Bahk, and John E. Bowers, “Semimetal/semiconductor nanocomposites for thermoelectrics”, Advanced Materials, 23, 2377 (2011).

Biography :

Dr. Hong Lu received her BS degree in Chemistry from University of Science and Technology of China, and PhD in Chemistry from the City University of New York in 2007. Her PhD research was focused on intersubband transitions of wide bandgap II-VI semiconductors grown by MBE. She is currently working in University of California at Santa Barbara (UCSB) as a project scientist. Her current research areas include using and developing MBE growth techniques for synthesis of materials and material structures, and characterization and processing for fundamental understanding and device applications, especially applications in thermoelectrics. Other research interests include two dimensional electron gas for electronic spin states control and rare earth-V compounds in III-V semiconductors for ultrafast photoconductive switches and THz based technology. Dr. Lu has coauthored in more than 40 papers in refereed journals.

    **************************************** ALL ARE WELCOME ****************************************

Enquiries: Ms. Winnie Wong, Department of Mechanical and Automation Engineering, CUHK at 3943 8337. *MAE Series (2012-13) is contained in the World-Wide Web home page at http://www3.mae.cuhk.edu.hk/maeseminars.php#mae.