TY - CHAP
T1 - Phonon properties
T2 - Phonon and free charge carrier properties in monoclinic-symmetry β-Ga2O3
AU - Schubert, Mathias
AU - Mock, Alyssa
AU - Korlacki, Rafał
AU - Knight, Sean
AU - Monemar, Bo
AU - Goto, Ken
AU - Kumagai, Yoshinao
AU - Kuramata, Akito
AU - Galazka, Zbigniew
AU - Wagner, Günther
AU - Tadjer, Marko J.
AU - Wheeler, Virginia D.
AU - Higashiwaki, Masataka
AU - Darakchieva, Vanya
N1 - Funding Information:
Acknowledgements This work was supported in part by the National Science Foundation under award DMR 1808715, by Air Force Office of Scientific Research under award FA9550-18-1-0360, by the Nebraska Materials Research Science and Engineering Center under award DMR 1420645, and by the Knut and Alice Wallenbergs Foundation grant 2018-2023 “Wide-bandgap semiconductors for next generation quantum components”. We acknowledge support from the Swedish Energy Agency under award P45396-1, the Swedish Research Council VR under award No. 2016-00889, the Swedish Foundation for Strategic Research under Grant Nos. FL12-0181, RIF14-055, and EM16-0024, and the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University, Faculty Grant SFO Mat LiU No. 2009-00971. M. S. acknowledges support by the University of Nebraska Foundation and the J. A. Woollam Foundation.
Publisher Copyright:
© Springer Nature Switzerland AG 2020.
PY - 2020
Y1 - 2020
N2 - We present and discuss the complete set of infrared-active phonon modes in monoclinic-symmetry crystal modification gallium oxide (gallia, β-Ga2O3). The phonon mode set is obtained from a comprehensive analysis of generalized spectroscopic ellipsometry data in the farinfrared and infrared spectral regions investigating various n-type electrically conductive single crystal samples with different free electron volume density parameters cut under different orientations. The analysis of the ellipsometry data is performed using an eigendielectric displacement vector summation (EDVS) approach. In this approach, the effect of the free charge carriers onto the lattice modes of intrinsic β-Ga2O3 are removed by calculation. Density functional theory calculations are performed in the general gradient approximation and all phonon modes at the Brillouin-center and their displacement direction dependencies are obtained. Transverse and longitudinal optical phonon mode parameters polarized within the monoclinic plane as well as perpendicular to the monoclinic plane agree excellently between experiment and theory. We also present and discuss the directional limiting frequency parameters within the monoclinic plane, the shape and anisotropy of the reststrahlen band, and the order of the phonon modes in semiconductors with polar phonon modes and monoclinic crystal structure. We further present and discuss the effect of coupling of longitudinal optical phonons with free charge carriers, leading to longitudinal-phonon-plasmon coupled modes. We reveal that the coupled modes, which affect electric and thermal transport, change amplitude, frequency, and direction within the monoclinic plane as a function of free electron concentration. Finally, we show optical Hall effect measurements, and provide experimentally determined effective electron mass parameters in β-Ga2O3 for moderately-doped n-type samples.
AB - We present and discuss the complete set of infrared-active phonon modes in monoclinic-symmetry crystal modification gallium oxide (gallia, β-Ga2O3). The phonon mode set is obtained from a comprehensive analysis of generalized spectroscopic ellipsometry data in the farinfrared and infrared spectral regions investigating various n-type electrically conductive single crystal samples with different free electron volume density parameters cut under different orientations. The analysis of the ellipsometry data is performed using an eigendielectric displacement vector summation (EDVS) approach. In this approach, the effect of the free charge carriers onto the lattice modes of intrinsic β-Ga2O3 are removed by calculation. Density functional theory calculations are performed in the general gradient approximation and all phonon modes at the Brillouin-center and their displacement direction dependencies are obtained. Transverse and longitudinal optical phonon mode parameters polarized within the monoclinic plane as well as perpendicular to the monoclinic plane agree excellently between experiment and theory. We also present and discuss the directional limiting frequency parameters within the monoclinic plane, the shape and anisotropy of the reststrahlen band, and the order of the phonon modes in semiconductors with polar phonon modes and monoclinic crystal structure. We further present and discuss the effect of coupling of longitudinal optical phonons with free charge carriers, leading to longitudinal-phonon-plasmon coupled modes. We reveal that the coupled modes, which affect electric and thermal transport, change amplitude, frequency, and direction within the monoclinic plane as a function of free electron concentration. Finally, we show optical Hall effect measurements, and provide experimentally determined effective electron mass parameters in β-Ga2O3 for moderately-doped n-type samples.
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U2 - 10.1007/978-3-030-37153-1_28
DO - 10.1007/978-3-030-37153-1_28
M3 - Chapter
AN - SCOPUS:85084669681
T3 - Springer Series in Materials Science
SP - 501
EP - 534
BT - Springer Series in Materials Science
PB - Springer
ER -