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<div align="center"><font face="Times New Roman"
color="#000000"><b>Seminar on</b></font></div>
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<div align="center"><font face="Times New Roman"
color="#000000"><b>Modern Optics and Spectroscopy</b></font></div>
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color="#000000"><b><br></b></font></div>
<div align="center"><font face="Times New Roman"
color="#000000"><i><b>Optical spectroscopy of individual carbon
nanotube p-n diodes</b></i></font></div>
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color="#000000"><i><b><br></b></i></font></div>
<div align="center"><font face="Times New Roman" color="#000000"><b>Ji
Ung Lee</b>,</font></div>
<div align="center"><font face="Times New Roman"
color="#000000"> University of Albany, SUNY</font></div>
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color="#000000"><br></font></div>
<div align="center"><font face="Times New Roman"
color="#000000">Tuesday, March 3, 2009</font></div>
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<div align="center"><font face="Times New Roman" color="#000000">12:00
- 1:00 p.m.</font></div>
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<div align="center"><font face="Times" color="#000000">The<i> p-n</i>
junction diode is the basis for nearly all-modern semiconductor
electronics. It is the basis for most transistors and optical devices.
The<i> p-n</i> structure is also useful for studying fundamental
materials properties. Here, we show that a carbon nanotube<i> p-n</i>
diode can provide a comprehensive probe of the optical and electronic
transitions in SWNTs. The<i> p-n</i> doping is achieved using a
split gate structure that electrostatically dopes the two ends of a
single nanotube. The resulting diode can exhibit an ideal diode
behavior, the theoretical limit of performance for any diode. In
the photocurrent spectra, an alternating sequence of resonant peaks
from the dissociation of excitons and exciton-phonon bound states is
observed, for the lowest and higher electronic subbands. At an
intermediate energy, the onset of continuum is observed that allows
measurements of exciton binding energies. The measured binding
energies are large (>0.25eV), and both the binding energy and the
onset of continuum follow the inverse diameter relation as expected
from general theory of optical transitions in nanotubes. In
addition to the energy levels revealed in the photocurrent spectra,
detailed transport measurements provide a complete set of energy
levels of the<i> p-n</i> structure. Specifically, we demonstrate
that bandgap renormalization, the shrinkage of the fundamental bandgap
due to many-body exchange-correction properties of interaction
electrons, dramatically alters the electronic structure, resulting in
the formation of heterointerfaces along a homogeneous
material. </font></div>
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<div align="center"><font face="Times New Roman" color="#000000">Grier
Room, MIT Bldg 34-401</font></div>
<div align="center"><font face="Times New Roman"
color="#000000">Refreshments served after the lecture</font></div>
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