Download Proposal for nano science and technology project on nitride based

Using quantum dots and nanograting to improve emission efficiency of
III-nitride based light-emitting diodes (LEDs)
PIs: 程育人, 施閔雄, 張亞中,(RCAS), 王興宗,(NCTU), 綦振瀛(NCU & RCAS)
This research proposal will focus on two areas: 1) Studies of cavity exciton-polaritons in
III-nitride with and without quantum dots and the dependence of emission efficiency on
exciton-photon coupling. 2) Effects of nano-scale grating and geometry on the emission
efficiency. The goal is to understand scientific issues of the exciton-photon (light-matter)
interaction dynamics in III-nitride quantum well/dot LEDs and find ways to improve the
emission efficiency via nanotechnology.
The III-nitride based optoelectronic devices covers applications from solid state lighting,
high density optical data storage (blue/UV lasers) to high speed/power electronics. The III-nitride
based LED is considered the most promising device for energy efficient lighting application.
This material system also finds important applications in cavity polariton research due to its high
exciton binding energy and large oscillator strength. Research in III-nitride material and devices
are crucial for the next generation optoelectronic and energy devices. Many scientific and
technological issues related to III-nitride devices remain unsolved. For example, the
photoluminescence of III-nitride material was found to be much less sensitive to crystal defect
than other well developed III-V alloys, such as GaAs. III-nitride based microcavities can have
very large and fast optical nonlinearity. III-nitride growth technology still has a lot of room to
improve.
The strain built up from lattice-mismatch during growth usually leads to the formation of
crystal defects and/or self-assembled nano clusters. Aside from lattice-mismatch, the InGaN/InN
compound can also spontaneously form nano dots or clusters due to its phase segregation
property. These nano-scale embedded dots together with crystal dislocation defects all affect its
photoluminescent characteristics. We plan to investigate the optoelectronic properties and the
potential applications to energy efficient solid state lighting device. Furthermore, when excitons
in the excited semiconductor material interact with cavity photons in the strong interaction
regime, they can form a quasi bosonic particle state at room temperature, the so called cavity
polaritons. The condensation of polaritons can lead to spontaneous coherent radiation and have
applications in polariton lasers, nonlinear optics, and quantum information. In the past, the
research has been carried out in materials that can operate only under cryogenic temperature.
Recently, this scientific research has been moved to III-nitride material as it becomes more
available and promises a room temperature operation due to its large exciton binding energy. We
plan to study the exciton-photon interaction dynamics in III-nitride material and the polariton
laser realization.
We will also fabricate properly designed nanoscale photonic crystal cavity and couple it
with the III-nitride light-emitting device. We have internationally competitive expertise in laser
cavity, nanostructure electronic states and electromagnetic wave modeling, as well as
photonic-crystal cavity fabrication. We will explore the effect of exciton-photon coupling inside
the cavity and find the best design to optimize the extraction efficiency of light from the
III-nitride LEDs.
Research approaches:
1.
Develop fabrication processes that can produce controlled nano structures and quantum
dots in shape, size, and composition [1]. The formation of quantum dots often relies on the
self-assembled process, which is often induced by strain built up and/or subsequent annealing. It
always carries certain degrees of randomness. It is crucial to develop process parameters with
low degree of randomness.
2.
Characterize the optoelectronic properties, e.g. PL spectrum, temperature dependence, etc,
by various analysis tools (e.g. micro/nano PL/EL/Raman, NSOM, SEM, TEM, etc.) and compare
with theoretical simulation based on realistic models. The focus is to gain knowledge about the
dependence of quantum well/dot energy level and luminescent properties on its physical and
material parameters.
3.
Design photonic crystal cavity to optimize the light emission by using an efficient
plane-wave based Green’s function method developed by Y. C. Chang [2]. Once the best design
is found, the actual fabrication will be made by solid state fabrication processes [3]. The
fabrication procedure includes electron beam lithography, and plasma-assisted dry etching etc.
4.
Aside from the above practical application, cavity polariton dynamics is an important
scientific research subject. The device structure for realization can be a monolithically grown
quantum well(s)/dot(s) in vertical surface emitting cavity [4]. The cavity polariton dynamics will
be investigated by photoluminescent spectral measurement.
References:
[1]. C.-K. Chao, H.-S. Chang, T. M. Hsu, C.-N. Hsiao, C.-C. Kei, S.-Y. Kuo, and J.-I. Chyi , Nanotechnology,
17, 15, 3930, Aug. 2006; J.-I. Chyi et al., Phys. Rev. Lett. 96. 117401, (2006)
[2]. Y.-C. Chang, G. Li, H. Chu, J. Opsal, J. Opt. Soc. A 23, 638 (2006);Y. C. Chang, H. Chu, J. Opsal; US
patents 6867866B1 and 7038850B2.
[3]. M. H. Shih, W. Kuang, M. Bagheri, A. Mock, S. J. Choi, J. D. O’Brien and P. D. Dapkus, Appl. Phys. Lett.
90, 121116 (2007); M. H. Shih et al., IEEE Photon. Tech. Lett. 18, 535 (2006).
[4]. Y.-J. Cheng, J.-T. Chu, H.-C. Kuo, T.-C. Lu, and S.-C. Wang, Frontiers in Optics, postdeadline paper
PDP-B8, (2007); Y.-J. Cheng, PRL 97, 093601, 2006.