Wednesday, May 14, 2014
Spalding Laboratory 106 Caltech campus
Advanced Semiconductor Devices: From Nanotechnology-based Photovoltaics to Infrared Thermal Sensing
A Materials Research Lecture By Dr. Giacomo Mariani, Jet Propulsion Laboratory
Modern semiconductor electronics has enabled the development of several novel functionalities in medicine, transport, energy, or sensing. One key functionality is represented by converting and sensing electromagnetic radiation: from efficient solar energy conversion to accurate radiometry in planetary missions.
In the first part of the talk, solar radiation is converted into electricity. Nanotechnology-based photovoltaics represents a viable route to reduce the amount of semiconductor material utilized to achieve high conversion efficiency at a lower dollar/watt figure. Dome-shaped nanolenses  atop radial nanopillar junctions can maximize the photon coupling compared to planar architectures with experimental power conversion efficiencies above 10%. Ex-situ and in-situ surface passivations are also compared to alleviate the recombination effects caused by dangling bonds at the junction .
In the second part of the talk, infrared radiation is sensed via thermopile technology. Thermopile detectors are based on the Seebeck effect: at the junction of two dissimilar conductors a voltage can be generated by a change in temperature. Thermopile arrays do not require electrical bias, and generate a voltage output linearly proportional to the input radiation signal. Typically they are uncooled and insensitive to substrate temperature variations, relaxing constraints on temperature stabilization. Efforts at the Jet Propulsion Laboratory  advanced this technology to a point that it was recently exploited for global thermal profiling of the martian atmosphere and lunar surface.
 G. Mariani, Z. Zhou, A. Scofield, and D. L. Huffaker, Epitaxial GaAs core-multishell nanopillars photovoltaics featuring subwavelength optical concentrators, Nano Letters 13 (4), pp. 1632–1637, 2013.
 G. Mariani, A. Scofield, C.-H. Hung, and D. L. Huffaker, GaAs nanopillars-array solar cells employing in situ surface passivation, Nature Communications 4, p. 1497, 2013.
 M. Foote, M. Kenyon, T. Krueger, T. J. Schofield, D. J. McCleese, T. A. McCann, E. W. Jones, S. L. Soll, M. R. Dickie, S. Gaalema, W. Hu, Linear and 2-D thermopile detector arrays using high-Z thermoelectric materials, Proceedings ICT 2002.
Giacomo Mariani is currently a Caltech Postdoctoral Scholar at Jet Propulsion Laboratory working on uncooled thermopile detector arrays. He received his PhD degree from the Electrical Engineering Department at UCLA. His research interests are focused in advanced optoelectronic devices to investigate light-matter interactions (e.g. energy harvesting, detection). He earned his B.S. and M.S. degree in Electrical Engineering from University of Bologna, in 2006 and 2008, respectively.