Electro-modulation spectroscopy of van der Waals crystals

Speaker: Prof. Robert Kudrawiec
Affiliation: (1) Department of Semiconductor Materials Engineering, Wroclaw University of Science and Technology,  Wrocław, Poland, (2) PORT – Polish Center for Technology Development, Łukasiewicz Research Network, Wrocław, Poland

Electro-modulation spectroscopy, photoreflectance (PR) and contactless electroreflectance (CER), is a very sensitive and nondestructive absorption-like technique to investigate the electronic band structure of semiconductor materials and heterostructures [1, 2]. Van der Waals crystals are known for long time but for recent years some of them have garnered significant interest because of different reasons. For example since pioneering work on optical properties of MoS₂ layers [3], it is well established that the electronic band structure of MoS₂ strongly varies with the number of layers and exhibits indirect-to-direct band gap transition with the reduction of crystal size to a single layer. For recent years similar studies of optical properties and the electronic band structure have been performed for other van der Waals crystals such as MoSe₂, MoTe₂, WS₂, and WSe₂ but still a lot of them is unexplored experimentally by some experimental techniques including the electro-modulation spectroscopy. In this seminar I will present our recent progress in the application of PR and CER spectroscopy to study the direct optical transitions in van der Waals crystals and heterostructures containing van der Waals crystals.

[1] R. Kudrawiec and J. Misiewicz, Chapter 4: Optical modulation spectroscopy, Editor: A. Patane, Experimental techniques in semiconductor research, Springer (2012).
[2] R. Kudrawiec and W. Walukiewicz, Electromodulation spectroscopy of highly mismatched alloys, J. Appl. Phys. 126, 141102 (2019).
[3] K.F. Mak, Ch. Lee, J. Hone, J. Shan, and T.F. Heinz, Atomically Thin MoS₂: A New Direct-Gap Semiconductor, Phys. Rev. Lett. 105, 136805 (2010).

Seminar language: English

Chairman: Ireneusz Weymann