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- Schubert, Mathias, et al.
(författare)
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Phonon properties: Phonon and free charge carrier properties in monoclinic-symmetry ß-Ga2O3
- 2020
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Ingår i: Gallium Oxide. - Cham : Springer. - 9783030371524 - 9783030371555 - 9783030371531 ; , s. 501-534
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- We present and discuss the complete set of infrared-active phonon modes in monoclinic-symmetry crystal modification gallium oxide (gallia, ββ-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 ββ-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 ββ-Ga2O3 for moderately-doped n-type samples.
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| 2. |
- Spencer, Joseph A., et al.
(författare)
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A review of band structure and material properties of transparent conducting and semiconducting oxides: Ga2O3, Al2O3, In2O3, ZnO, SnO2, CdO, NiO, CuO, and Sc2O3
- 2022
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 9:1
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Forskningsöversikt (refereegranskat)abstract
- This Review highlights basic and transition metal conducting and semiconducting oxides. We discuss their material and electronic properties with an emphasis on the crystal, electronic, and band structures. The goal of this Review is to present a current compilation of material properties and to summarize possible uses and advantages in device applications. We discuss Ga2O3, Al2O3, In2O3, SnO2, ZnO, CdO, NiO, CuO, and Sc2O3. We outline the crystal structure of the oxides, and we present lattice parameters of the stable phases and a discussion of the metastable polymorphs. We highlight electrical properties such as bandgap energy, carrier mobility, effective carrier masses, dielectric constants, and electrical breakdown field. Based on literature availability, we review the temperature dependence of properties such as bandgap energy and carrier mobility among the oxides. Infrared and Raman modes are presented and discussed for each oxide providing insight into the phonon properties. The phonon properties also provide an explanation as to why some of the oxide parameters experience limitations due to phonon scattering such as carrier mobility. Thermal properties of interest include the coefficient of thermal expansion, Debye temperature, thermal diffusivity, specific heat, and thermal conductivity. Anisotropy is evident in the non-cubic oxides, and its impact on bandgap energy, carrier mobility, thermal conductivity, coefficient of thermal expansion, phonon modes, and carrier effective mass is discussed. Alloys, such as AlGaO, InGaO, (AlxInyGa1-x-y)(2)O-3, ZnGa2O4, ITO, and ScGaO, were included where relevant as they have the potential to allow for the improvement and alteration of certain properties. This Review provides a fundamental material perspective on the application space of semiconducting oxide-based devices in a variety of electronic and optoelectronic applications.& nbsp;Published under an exclusive license by AIP Publishing
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