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- ItemTransport Properties and Finite Size Effects in β-Ga2O3 Thin Films([London] : Macmillan Publishers Limited, part of Springer Nature, 2019) Ahrling, Robin; Boy, Johannes; Handwerg, Martin; Chiatti, Olivio; Mitdank, Rüdiger; Wagner, Günter; Galazka, Zbigniew; Fischer, Saskia F.Thin films of the wide band gap semiconductor β-Ga2O3 have a high potential for applications in transparent electronics and high power devices. However, the role of interfaces remains to be explored. Here, we report on fundamental limits of transport properties in thin films. The conductivities, Hall densities and mobilities in thin homoepitaxially MOVPE grown (100)-orientated β-Ga2O3 films were measured as a function of temperature and film thickness. At room temperature, the electron mobilities ((115 ± 10) cm2/Vs) in thicker films (>150 nm) are comparable to the best of bulk. However, the mobility is strongly reduced by more than two orders of magnitude with decreasing film thickness ((5.5 ± 0.5) cm2/Vs for a 28 nm thin film). We find that the commonly applied classical Fuchs-Sondheimer model does not explain sufficiently the contribution of electron scattering at the film surfaces. Instead, by applying an electron wave model by Bergmann, a contribution to the mobility suppression due to the large de Broglie wavelength in β-Ga2O3 is proposed as a limiting quantum mechanical size effect.
- ItemTemperature dependence of the Seebeck coefficient of epitaxial β -Ga2O3 thin films(Melville, NY : AIP Publ., 2019) Boy, Johannes; Handwerg, Martin; Ahrling, Robin; Mitdank, Rüdiger; Wagner, Günter; Galazka, Zbigniew; Fischer, Saskia F.The temperature dependence of the Seebeck coefficient of homoepitaxial metal organic vapor phase grown, silicon doped β-Ga 2 O 3 thin films was measured relative to aluminum. For room temperature, we found the relative Seebeck coefficient of Sβ-Ga2O3-Al=(-300±20) μV/K. At high bath temperatures T > 240 K, the scattering is determined by electron-phonon-interaction. At lower bath temperatures between T = 100 K and T = 300 K, an increase in the magnitude of the Seebeck coefficient is explained in the frame of Stratton's formula. The influence of different scattering mechanisms on the magnitude of the Seebeck coefficient is discussed and compared with Hall measurement results. © 2019 Author(s).