Current Research Interests
Highly Ordered Quantum Dot Arrays
Our current research focuses on the fabrication and materials analysis of highly ordered semiconductor quantum dot arrays.
This work is based on the motivation to extend the results and good properties of self-assembled quantum dots to an unprecedented level by utilizing a self-organized approach to create lateral superlattices of quantum dots with high packing density and uniform size, shape, and spacing.
The foundation of our approach is rooted in the use of an anodized aluminum oxide (AAO) template which self-organizes into a porous hexagonal array (Figure 1) under controlled conditions. This template is used as a mask to create nanopores in a semiconductor substrate via reactive ion etching (RIE). The quantum dots are then grown in these nanocavities by molecular beam epitaxy (MBE). Significant advantages to this fabrication process are that it is non-lithographically based and it can be scaled to large areas. The AAO template has also been used for fabricating various other nanostructures, including nanodots and nanopillars.
Work performed by previous members in our group has demonstrated a growth pathway for highly ordered InAs quantum dots in GaAs nanopore arrays. 1 The size and spacing of the InAs quantum dots followed that of the AAO template (55 nm and 110 nm, respectively), while x-ray and TEM results indicated high quality InAs. A current example of InAs quantum dots grown in GaAs nanopores is shown in Figure 2. SiO 2 -assisted growth of InAs, where the surface interaction of the nanopatterned SiO 2 layer and InAs facilitates nucleation of the quantum dots, is demonstrated in Figure 3.
Currently, we are optimizing our fabrication methods in order to better understand the process window for this type of directed growth. In combination with other analysis methods, specifically photoluminescence (PL) and PL mapping, we seek to improve upon the quality of quantum dot-based devices including lasers and detectors by fabricating three-dimensionally confined nanostructures.
1. Liang, J. Y., H. L. Luo, R. Beresford et al. , "A growth pathway for highly ordered quantum dot arrays", Appl. Phys. Lett. 85 (24), 5974-5976 (2004).
Figure 1. SEM top view of a typical AAO template on a GaAs substrate. Top-left inset is the FFT of the SEM image; bottom-left inset is the pore size distribution.
Figure 2. SEM top view of InAs quantum dots grown by molecular beam epitaxy in a GaAs nanopore array.
Figure 3. SEM top view of InAs quantum dots grown using a nanopatterned SiO 2 mask on a GaAs substrate.
- Ph.D. Materials Science and Engineering, Northwestern University (2003)
- B.S. Materials Science and Engineering, Northwestern University (1998)