Semiconductor Quantum Dots: From Trap-States to Charge Stabilization and Single Photon Purity
Professor K. George Thomas
- Indian Institute of Science Education and Research Thiruvananthapuram (IISER)
Monday 21 November, 4.30pm
Abstract
Quantum confinement effects in semiconductor quantum dots (QDs) allowed newer possibilities in tuning their physical properties by varying the size and shape. The under coordinated atoms on the surface of QDs form dangling bonds and their periodic arrays give rise to bands. In binary QDs, these bands are formed within the bandgap, which traps the photogenerated charge carriers, often called trap states. Trapping of charge carriers increases the non-radiative decay pathways of excitons, thus decreasing the fluorescence quantum yield. Our studies have established that the optoelectronic properties of QDs are highly influenced by the trapping of charge carriers on the nanocrystal surface and the presentation will discuss the four aspects:
Understanding photoluminescence (PL) fluctuations in CdSe QDs using time-resolved photoluminescence spectroscopy at single-particle level by systematically varying its core size and maintaining a constant shell thickness.
Establishment of the existence of trap states in CdSe-CdS systems by concurrent investigation of PL fluctuations and HRTEM analysis, and its influence on photophysical properties.
Approaches to enhance the single photon purity by suppressing the biexciton emission, in semiconductor quantum dots analysed using second-order photon correlation studies.
Demonstration of the presence of deep trap states in InP which retards the charge recombination to sub-millisecond timescale as compared to QDs having shallow trap states. The role of the size of InP QDs on their In/P stoichiometry and the trap state distribution will also be discussed.
1. E. K. Vishnu, A. A. K. Nair, and K. George Thomas, J. Phys. Chem. C, 125, 25706 (2021).
2. E. M. Thomas, N. Pradhan, K. George Thomas, ACS Energy Lett., 7, 2856 (2022).
3. Thomas, K. Sandeep, S. M. Somasundaran, K. George Thomas, ACS Energy Lett. 3, 2368 (2018).
4. E. K. Vishnu, A. A. K. Nair, and K. George Thomas (under publication 2022).
About the speaker
George Thomas is a professor and J C Bose National Fellow at the School of Chemistry of the Indian Institute of Science Education and Research Thiruvananthapuram. He received his PhD degree in Chemistry from the University of Kerala and afterwards worked as senior scientist in the Photosciences & Photonics Section of the CSIR-National Institute for Interdisciplinary Science & Technology from July 1994 to April 2010.
In May 2010, he accepted an invitation from the newly established Indian Institute of Science Education and Research Thiruvananthapuram and joined as a Professor. Twenty students completed their doctoral degree under his supervision now occupying important positions as faculty members in prestigious Indian and foreign Universities.
He served as the founding Dean (Academics and Faculty Affairs) of IISER Thiruvananthapuram (2010-2015) and now serving as Dean (Faculty Affairs) since March 2020. He is instrumental in building IISER Thiruvananthapuram in various capacities. He also served as the Director (additional charge) of IISER Thiruvananthapuram during June 07 2013 – Feb. 13, 2014
He is currently the President of the Asian and Oceanian Photochemistry Association (APA) and was the member of editorial advisory committee of the Journal of Physical Chemistry of the American Chemical Society during the period 2012–2015.
George Thomas is a recipient of several awards and distinctions: most significant ones are the J C Bose National Fellowship (2014-2019 and 2019-2024), one of the highest national research fellowships with a research grant and the prestigious Shanti Swarup Bhatnagar Prize in Chemical Sciences (2006), the highest annual science award given for a researcher below the age of 45 years.
He is an elected fellow of Indian National Science Academy, New Delhi (2015) and Indian Academy of Sciences, Bangalore (2007) (two national science academies of India) and Honorary Professor of the Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore.
