Bhopal, 11th April 2023: Indian Institute of Science Education and Research Bhopal researchers explore the properties of transition metal dichalcogenides (TMDs), a class of advanced two-dimensional materials with unique electrical, optical, and mechanical properties.
The research on one kind of TMDs – Molybdenum Disulphide (MoS2) nanosheets, could pave the way for the development of advanced optoelectronic devices such as phototransistors, light detectors, light-emitting diodes (LEDs) and solar cells. The findings of this research have recently been published in The Journal of Physical Chemistry C, and Surface and Interface Analysis. The research is led by Dr. K. V. Adarsh, Professor, Department of Physics, IISER Bhopal, and his research scholars Ms. Pravrati Taank, and Ms. Riyanka Karmakar, who contributed equally to this work.
TMDs such as MoS2 nanosheets are semiconducting 2D layered materials, and their thickness-dependent band gap makes them a potential material for optoelectronic devices. Previous research has reported the existence of free carriers and excitons, which are particles produced when an electron is excited by light. These carriers play a vital role in electronic and optoelectronic applications. Scientists have conducted several studies to understand how these carriers behave when generated by light. These studies have shown that various factors, such as defects, free carriers, lattice heating, and sample processing, can affect carrier dynamics. However, distinguishing between them has been challenging.
Dr. K.V. Adarsh and his Ph.D. students, Ms. Pravrati Taank, Ms. Riyanka Karmakar, Dr. Rituraj Sharma, Dr. Rajesh Kumar Yadav, Dr. Megha Shrivastava, and Mr. Naresh Chandra Maurya and other co-authors Dr. Debjani Karmakar from BARC, Mumbai used an advanced technique called femtosecond transient absorption spectroscopy to study how light interacts with few-layer MoS2 nanosheets. Their work found clear evidence of two types of charge particles – excitons and free carriers, that behave differently based on the amount of energy used to excite them.
The researchers found that high-energy light produces excitons and free carriers, but the excitons disappeared quickly due to defects. Free carriers, on the other hand, lingered for up to a nanosecond (a hundred thousandth of a second). Low-energy light only produced excitons, which disappeared quickly.
“Our systematic studies in few-layer MoS2 nanosheets reveal crucial information on the unexplored domain of excitons and free carriers’ recombination in the presence of defects for several optoelectronic applications,” said Dr. K.V. Adarsh, IISER Bhopal.
The scientists have also examined the characteristics of defects and studied various configurations of sulphur vacancies using density functional theory (DFT) and time-dependent DFT.
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