Speaker:
Dr. Zbig Wasilewski
Institute for Microstructural Sciences, National Research Council, Ottawa
Title:
MBE Growth of THz Quantum Cascade Lasers-Towards High-temperature Operation
Date:
Thursday, November 24, 2011
Time:
11:00 am - 12:00 noon
Location:
E5 5106/5128
Abstract:
The temperature performance of terahertz (THz) quantum cascade lasers
(QCL) has been continuously improving to the point that the empirical
limit of the maximum thermal energy, kBTmax, to the photon energy has
been surpassed in devices emitting from 1.2 THz to 3.3 THz, which makes
these photonic devices unique. Increasing the operating temperatures to
commercially available thermoelectric coolers range (about 240 K) will
make THz QCLs very attractive to a broad range of potential applications
in areas such as biological sensing, pharmaceutical sciences, THz wave
imaging and hazardous materials detection, to mention just a few. In
2007 we proposed the simplest at the time THz QCL design based on a
three quantum well active module[1], which proved to be particularly
effective in increasing the population inversion and hence the gain at
higher temperatures. Indeed, in 2008, Belkin et al[2] demonstrated
with this exact design a lasing temperature of 178K, using low-loss
copper metal-metal waveguides, while in 2009 a temperature of 186K
was reported by Kumar et al[3] using a diagonal variation of the three
well design with small leakage channels. The relative simplicity of this
design permitted us to conduct a series of experimental studies, using a
unique to molecular beam epitaxy (MBE) capability [4] of well controlled
variation of only one structure parameter across the substrate, while
retaining excellent spatial uniformity for the remaining parameters[5,6].
The same simplicity has also helped to develop an analytical model [7]
explaining the observed trends, giving us a valuable tool to further
optimize laser performance. This effort, conducted in collaboration
between our institute and University of Waterloo, resulted recently in
a new world record Tmax of 195K [8]. Even though the achieved operating
temperatures have already surpassed "reasonable" expectations, there
is no obvious barrier which would prevent these devices from operating
even at room temperature. However, further progress will demand the very
best of all "creation" stages: (i) modelling/design, (ii) MBE growth
and (iii) fabrication.
In this talk we present an account of this quest with emphasis on the
molecular beam epitaxial process and related challenges. A compact
overview of MBE technology and its capabilities will be given as an
introduction.
[1] H. Luo, S. R. Laframboise, Z. R. Wasilewski, G. C. Aers, H. C. Liu, and J. C. Cao, Appl. Phys. Lett. 90 (2007) 041112.
[2] M. A. Belkin, J. A. Fan, S. Hormoz, F. Capasso, S. P. Khanna, M. Lachab, A. G. Davies, and E. H. Linfield, Opt. Express 16 (2008) 3242.
[3] S. Kumar, Q. Hu, and J. L. Reno, Appl. Phys. Lett. 94 (2009) 131105.
[4] Z. R. Wasilewski, G. C. Aers, A. J. SpringThorpe, and C. J. Miner, J. Vac. Sci. Technol. B 9 (1991) 120.
[5] H. Luo, S. R. Laframboise, Z. R. Wasilewski, H. C. Liu, and J. C. Cao, Electron. Lett. 44 (2008) 630.
[6] H. Luo, S. R. Laframboise, Z. R. Wasilewski, and H. C. Liu, Electron. Lett. 43 (2007) 633.
[7] E. Dupont, S. Fathololoumi, and H. C. Liu, Phys. Rev. B 81 (2010) 205311.
[8] S. Fathololoumi, E. Dupont, C.W.I. Chan, Z.R. Wasilewski, S.R. Laframboise, D. Ban, A. Matyas, C. Jirauschek, Q. Hu and H. C. Liu, Opt. Express, in preparation.
Biography:
Z. R. Wasilewski received the Ph.D. degree from the Institute of Physics,
Polish Academy of Sciences, Warsaw, Poland, in 1986. His doctoral work
focused on the influence of high hydrostatic pressure on the magneto
optical properties of shallow and deep donors in InSb. He joined the
National Research Council of Canada, Ottawa, ON, Canada, in 1988 after
one year of Postdoctoral Fellowship with the Imperial College of Science
and Technology, London, U.K.
Since 1989, his work has been focused primarily on the molecular
beam epitaxial growth and characterization of III-V semiconductor
compounds. He currently holds the position of Principal Research Officer
in the Institute for Microstructural Sciences, National Research Council
of Canada. He is a coauthor of over 390 refereed journal articles and
conference proceedings.
