Modeling Raman and Photoluminescence Spectra of Defective Materials

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School of Science | Doctoral thesis (article-based) | Defence date: 2023-01-27
Degree programme
72 + app. 68
Aalto University publication series DOCTORAL THESES, 5/2023
Defects are inevitable in solid materials as a result of fluctuations in thermal equilibrium and their processing kinetics. Depending on the targeted application, they can be either beneficial or detrimental. For example, doping semiconductors by foreign atoms can be used to increase carrier concentrations, but at the same time, the carrier mobilities decrease due to enhanced scattering. Defects can also introduce a two-state light emitter system to compensate for the indirect nature of the electronic band gap. However, it is necessary to elucidate the presence of defects and their influence on the properties of materials to develop an application-specific strategy for defect engineering. Raman spectroscopy can be utilized as a contactless and inexpensive diagnostic tool to characterize materials and evaluate their qualities. Photoluminescence spectroscopy is another non-destructive technique that helps us to understand the behavior of optically active defects in materials. While experimental measurements can be complicated, modern computational platforms possess good predictive power and can give us a deep insight into the relevant physical processes. In the case of defects, one needs high computational resources and an advanced theoretical framework to calculate Raman spectra. These issues need to be tackled in a reliable way before calculations. This thesis focuses on simulating Raman and photoluminescence spectra to investigate defects signatures in materials. An efficient computational method to simulate Raman spectra of large systems, which applies to alloys and systems with a small number of defects is devised. The method is based on the projection of vibrational eigenvectors of the supercell to the eigenvectors from the pristine primitive unit cell and using the Raman tensors calculated for the latter. Using photoluminescence and accounting for electron-phonon interactions, we investigate vibronic structures of color centers and calculate phonon side bands. Through this thesis, the behavior of phonons in several two-dimensional semiconducting alloys is explored. We demonstrate that (i) the so-called mass approximation significantly facilitates the calculation of Raman spectra, (ii) simulating the Raman spectra for defective materials can be done by a combination of empirical potentials and quantum mechanical density functional theory calculations, (iii) the so-called phonon confinement model can be used to capture the asymmetric broadening of the prominent peaks. In the context of photoluminescence, we compare the vibronic structures of different color centers by evaluating several important characteristics that are experimentally achievable.
Supervising professor
Ala-Nissilä, Tapio, Prof., Aalto University, Department of Applied Physics, Finland; Puska, Martti, Emeritus Prof., Aalto University, Finland
Thesis advisor
Krasheninnikov, Arkady, Dr., Helmholtz-Zentrum Dresden-Rossendorf, Germany
Komsa, Hannu-Pekka, Dr., University of Oulu, Finland
Raman spectroscopy, photoluminescence, phonon, defect, two-dimensional, empirical potential, density functional theory, mass approximation, Phonon confinement model, vibronic structure
Other note
  • [Publication 1]: A. Hashemi, A. V. Krasheninnikov, M. J. Puska, and H.-P. Komsa. Efficient method for calculating Raman spectra of solids with impurities and alloys and its application to two-dimensional transition metal dichalcogenides. Physical Review Materials, Volume 3, Issue 2, 023806, February 2019.
    Full text in Acris/Aaltodoc:
    DOI: 10.1103/PhysRevMaterials.3.023806 View at publisher
  • [Publication 2]: S. M. Oliver, J. J. Fox, A. Hashemi, A. Singh, R. L. Cavalero, S. Yee, D. W. Snyder, R. Jaramillo, H.-P. Komsa, P. M Vora. Phonons and excitons in ZrSe2-ZrS2 alloys. Journal of Materials Chemistry C, Volume 8, Issue 17, 5732-5743, March 2020.
    DOI: 10.1039/d0tc00731e View at publisher
  • [Publication 3]: Z. Kou, A. Hashemi, M. J. Puska, A. V. Krasheninnikov, H.-P. Komsa. Simulating Raman spectra by combining first-principles and empirical potential approaches with application to defective MoS2. npj Computational Materials, Volume 6, Issue 1, 1-7, May 2020.
    Full text in Acris/Aaltodoc:
    DOI: 10.1038/s41524-020-0320-y View at publisher
  • [Publication 4]: Z. Shang, A. Hashemi, Y. Berencen, H.-P. Komsa, P. Erhart, S. Zhou, M. Helm, A. V. Krasheninnikov, G. V. Astakhov. Local vibrational modes of Si vacancy spin qubits in SiC. Physical Review B, Volume 101, Issue 14, 144109, April 2020.
    DOI: 10.1103/PhysRevB.101.144109 View at publisher
  • [Publication 5]: V A. Hashemi, C. Linderälv, A. V. Krasheninnikov, T. Ala-Nissila, P. Erhart, H.-P. Komsa. Photoluminescence line shapes for color centers in silicon carbide from density functional theory calculations. Physical Review B, Volume 103, Issue 12, 125203, March 2021.
    Full text in Acris/Aaltodoc:
    DOI: 10.1103/PhysRevB.103.125203 View at publisher