Mathias Schubert, University of Nebraska-Lincoln, Phonons, free charge carriers, excitons and band-to-band transitions in beta Ga2O3 and related alloys determined by ellipsometry and optical Hall effect

Date: Mon. October 21st, 2019, 12:45 pm-1:45 pm
Location: Rockefeller 221 (Les Foldy Room)
Website: https://ncmn.unl.edu/faculty/schubert

Phonons, free charge carriers, excitons and band-to-band transitions in beta Ga2O3 and related alloys determined by ellipsometry and optical Hall effect

1. Schubert^1,2,3, A. Mock⁴, S. Knight¹, M. Hilfiker¹, M. Stokey¹, V. Darakchieva², A. Papamichail², R. Korlacki¹, M.J. Tadjer⁵, Z. Galazka⁶, G. Wagner⁶, N. Blumenschein⁷, A. Kuramata⁸, K. Goto^8,9, H. Murakami⁹, Y. Kumagai⁸, M. Higashiwaki¹⁰, A. Mauze¹¹, Y. Zhang¹¹, J. S. Speck¹¹

 

¹Department of Electrical and Computer Engineering, University of Nebraska – Lincoln, Nebraska 68588, USA

²Department of Physics, Chemistry and Biology (IFM), Linkoping University, SE 58183 Linkoping, Sweden

³Leibniz Institute for Polymer Research, 01069 Dresden, Germany

⁴National Research Council Postdoctoral Fellow, residing at U.S. Naval Research Laboratory, Washington, DC 20375 USA

⁵U.S. Naval Research Laboratory Electronics Science and Technology Division, Washington, DC 20375, USA

⁶Leibniz-Institut für Kristallzüchtung, Berlin 12489, Germany

⁷Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695, USA

⁸Novel Crystal Technology, Inc. Saitama, Japan

⁹Department of Applied Chemistry, Tokyo University of Agriculture and Technology, Koganei, Tokyo, Japan

¹⁰National Institute of Information and Communications Technology, Koganei, Tokyo, Japan

¹¹Materials Department, University of California Santa Barbara, Santa Barbara, CA 93106, USA

 

Email: schubert@engr.unl.edu

We discuss the analysis of the dielectric function tensor for monoclinic metal oxides obtained from generalized spectroscopic ellipsometry. We investigate the potential high-power device material gallium oxide and derive dispersions of transverse, longitudinal and plasmon coupled modes [Phys. Rev. B 93, 125209 (2016); Editors’ Suggestion] and the band-to-band transitions and excitons along with their eigenvectors [Phys. Rev. B 96, 245205 (2017)]. Additionally, we show that this technique can fully explain the unusual ordering of optical phonon mode pairs which is observed in beta-Ga2O3 [Phys. Rev. B 99, 041201(R) (2019)] as well as their dependency on free charge carrier concentrations. [Appl. Phys. Lett. 114, 102102 (2019); Editor’s Pick].  We apply this technique also for the identification of transverse and longitudinal phonons in monoclinic scintillator material cadmium tungstate [Phys. Rev. B 95, 165202 (2017)], and high-power laser materials yttrium orthosilicate [Phys. Rev. B, 97 165203 (2018)] and lutetium orthosilicate [under review]. We apply our technique to investigate the effective electron mass tensor using optical Hall effect measurements [Appl. Phys. Lett. 112, 012103 (2018); Editors’ Pick], the temperature dependence of band-to-band transitions energies [Appl. Phys. Lett. 112, 041905 (2018)], and the effects of aluminum alloying concentration onto the band-to-band transition energies [Appl. Phys. Lett. 114, 231901 (2019)]. We further apply our technique to epitaxial layers of beta-phase gallium oxide and discuss the relationship between the X-ray diffraction measured strains with respect to the optically determined shifts in transverse optical phonon modes as compared to the bulk material. Understanding of the stress and strain relationship to properties in monoclinic materials will help facilitate better control of material properties for engineering next generation power devices based on beta-Ga2O3.

Host: Walter Lambrecht