报告人：Cun-Zheng Ning 教授
School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, AZ 85287, email: firstname.lastname@example.org,
题目: Semiconductor Alloy Nanowires for Optoelectronic Applications from UV to Midinfrared
Bandgap is one of the most important parameters of a semiconductor material for optoelectronic applications since they determine the spectral features of absorptions and emission processes. Many applications such as lasers, solar cells, detectors, and LEDs can benefit greatly from semiconductors with any desired bandgaps or variable bandgaps in a wide range. This has been a challenging task for the traditional planar epitaxial technology. Nanomaterials such as nanowires open new opportunities of bandgap engineering through alloying with almost arbitrary compositions.
In this talk, recent results are presented on growing and characterizing spatially composition-controlled alloys by combining spatial gradient of source materials with a temperature gradient in a CVD system. Using this dual gradient method, it will be demonstrated that a continuous spatial composition grading of single-crystal quaternary ZnxCd1-xSySe1-y alloy nanowires can be achieved over the complete bandgap range along the length of a substrate. The bandgap changes continuously from 3.55 eV (ZnS) to 1.75 eV (CdSe) on a single substrate, with the corresponding light emission over the entire visible spectrum. Further extension of bandgaps to mid-infrared wavelength range is made possible by alloying CdS with PbS. We also showed that the dual gradient method can be extended to achieve alloy composition control in two spatial dimensions, and possibly for color engineering. Various characterization results will be presented including, SEM, TEM, XRD, PL to confirm alloy properties.
Such unique alloy nanowire materials capabilities enable an array of new devices applications. These include nanowire lasers that can tune over 200 nm in wavelength, a new multiple lateral solar cells with efficiency comparable to the more expensive triple junctions cells at a potentially much less cost, or multispectral detectors in a wide spectral range. These and other examples of applications of alloy nanowires will be discussed.
Cun-Zheng Ning received his PhD (Dr. rer. nat.) in Physics from the University of Stuttgart, Germany, in 1991. He has published over 150 papers including many in high impact journals such as Physical Review Letters (6), Nano Letters (6)., ACS Nano (2), Proceedings of National Academy of Sciences (1), and Advanced Materials (1), J. Am. Chem. Soc. (1), in the areas of laser physics, geometric phases, quantum optics, semiconductor optoelectronics, many-body physics in semiconductors, nanophotonics and nanolasers. He has also presented over 110 invited, plenary, or colloquium talks worldwide. He was a senior scientist, Nanophotonics Group leader, and Nanotechnology Task manager at NASA Ames Research Center from 1997 to 2007, and an ISSP Visiting Professor at University of Tokyo in 2006. Since 2006, he has been professor of electrical engineering, and Affiliate Professor in Physics and in Materials Science and Engineering at Arizona State University. He was winner of several awards including NASA and NASA contractor Achievement Awards, NASA Space Act Patent Awards, CSC Technical Excellence Award, and IEEE/Photonics Society Distinguished Lecturer from 2007-2009. He has made several pioneering theoretical and experimental contributions in laser physics, nonlinear sciences, and nanophotonics. Notable among them are Ning-Haken or Landsberg-Ning-Haken formalism for geometric phases, stochastic resonances without external forces, first realization of single nanowire infrared laser, first realization of quaternary nanomaterial, first lasers beyond diffraction limit, and first room temperature operation of subwavelength nanolasers. Many of his recent achievements are highlighted in Science, Nature Photonics, Laser Focus World, Photonics Spectra, Materials Today, MRS Bulletin, and many other technology magazines worldwide. Further information about his group can be found at http://nanophotonics.asu.edu.