Scope of the Project
Background and Motivation
Nanocrystal quantum dots (NQDs) and quantum dot light emitting diodes (QD-LEDs) Semiconductor NQDs have recently commanded considerable attention from photonics researchers due to their unique optical characteristics and relatively straightforward processing. Semiconductor NQDs are nanocrystals that are smaller in size than the diameter of a Bohr exciton in a bulk crystal of the same material.
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Method of mist deposition
In the search for a more practical and effective solution to the challenges in the fabrication and patterning of multicolor QD-LED arrays, this project explores an alternative thin film formation method which is capable of quasi-conformal covering of solid surfaces with monolayer-accuracy, is mostly free from the inherent limitations of deposition techniques discussed earlier, and is compatible with selective area deposition.
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Research objectives and Project Thrusts
This study investigates and to employs a mist-deposition process in the assembly and patterning of NQDs in QD-LED fabrication. The processing variables that control the thickness, composition, morphology, and mesa patterning of the emissive NQD layer are investigated.
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Selected Results
NQD Film thickness control
The high-resolution TEM image shows that the mist-deposition of NQD CdSe film can be controlled down to a single-dot layer. By employing longer deposition time and/or varying nanodots concentration in the colloidal solution the NQD film thickness can be readily controlled.
Mist deposited NQD LEDs
The CdSe quantum dots featuring various sizes (3.5nm, 5.5nm, and 8.3nm) were mist deposited as an active layer in the LED structure on the ITO covered glass substrates. As a result, QD LEDs emitting different wavelengths were obtained.
NQD LEDs mist deposited on flexible substrates
The same as above process was reproduced using flexible substrates and working NQD CdSe-based LEDs were fabricated.
Feature Story
High quality CdSe quantum dots based LEDs were demonstrated using mist deposition process. As an example of performance, figure above shows current density and radiance power versus applied voltage for a red QD-LED fabricated with mist-deposition process. The insets show emission spectrum and image of the functional LED fabricated using methods introduced in this proposal.
Published Papers
T. Zhu, K. Shanmugasundaram, F. Zhang, S.C. Price, S. E. Mohney, Q. Zhang, A. Y. Wang, J. Ruzyllo and J. Xu , "Mist-Fabrication of Light Emitting Diodes with Colloidal Nanocrystal Quantum Dots", Applied Physics Letters, 92 (2), 023111 (2008)
S.C. Price, K. Shanmugasundaram, S. Ramani, T. Zhu, F. Zhang, J. Xu, S. Mohney,K. Kshirsagar, nd J. Ruzyllo, "Studies of Mist Deposition for the Formation of Quantum Dot CdSe Films", submitted to Semiconductor Science and Technology.
J. Xu, J, J. Ruzyllo, T. Zhu, K. Shammugasundaram, F. Zhang, S.C. Price, S. Mohney, Q. Zhang, A.Y. Wang, "Patterned Deposition of Solution-Processed Colloidal Nanocrystal Quantum Dots for LED Applications", Nanotech 2008 Conference and Trade Show, Boston, June 1-5, 2008.
A. Kshirsagar, S. Ramani, K. Shanmugasundaram, T. Zhu, K. Sridhara, S. Gao, Q. Zhang, S. Mohney, J. Xu and J. Ruzyllo, "Application of mist Deposition Process in the Formation of Quantum Nanodots Films", Electronic Material Conference 2009, University Park, PA, June 24-26, 2009