[Research Plan]

Photonic Crystals using Ordered Arrays of

Pyramidal Quantum Dots

[Introduction]

Photonic Crystal technologies now makes use of various interesting phenomena to control light in very small systems in a micro-meter scale[1]. This promises some important break-throughs in tele-communication technologies, such as extremely low loss waveguide systems[2], photonic crystal lasers[3,4], and potentially might bring about the realization of the world-smallest optical integrated circuits.

Nano-scale quantum dot (QD) technologies also are in their important stage to control only one electron in the well-controlled semiconductor structures[5,6].

In this research, I am going to combine these two world-forefront technologies to investigate the electron-light interactions in semiconductor nano-structures, and eventually to achieve the world-smallest well-controlled optical-electronic devices.

[Purpose]

Recently, Professor Kapon’s group in EPFL, Switzerland established a powerful technique to grow very uniform QD in pyramidal semiconductor structures[5,7](please see a figure below). Here, growth of QDs in inverted pyramids using self-ordering during organo-metallic chemical vapor deposition (OMCVD) on patterned substrates provides a unique way for preparing high optical quality, uniform QDs placed at predetermined locations.

I am going to join the Professor Kapon’s group in April 2002, and will try to make ordered arrays with such structures, thereby making it possible to achieve photonic crystals with well-characterized gain/absorption centers. These structures are very interesting for studies of the effect of optical gain and absorption on photonic crystals as well as for novel device applications, e.g., QD lasers or photonic crystal switches.

[Concrete research plans]

I propose to utilize these structures for studying the effect of the photonic crystal modes on the luminescence properties of QD arrays. Pyramidal QD arrays will be fabricated inside slab waveguides using electron beam lithography and OMCVD growth. The period and lattice structure will be designed so as to achieve Bragg reflection in the plane of propagation. The resulting photonic crystals will be studied first at low temperatures in a waveguide set-up permitting to launch a tunable laser beam into the structure. The absorption and luminescence spectra of the QD photonic crystals will be measured and compared to those obtained in a randomly arranged array of dots. Optical pumping of the structures will be used to evaluate the optical gain spectra and lasing in these structures will be explored. At a later stage, electrical injection into such QD arrays will be attempted using p-n junctions. Light emitting diode and diode laser structures based on such designs will be investigated.

[References]

[1] J. D. Joannopoulos, Nature (1997), 386, 143.

[2] J. C. Knight et al., Science (1998), 282, 476.

[3] O. Painter et al., Science (1999), 284, 1819.

[4] S. Noda et al., Science (2001), 293, 1123.

[5] A. Hartmann et al., Physical Review Letters (2000), 84, 5648.

[6] M. Bayer et al., Nature (2000), 405, 923.

[7] A. Hartmann et al., Applied Physics Letters (1998), 73, 2322.