Robin Ahrling | Searcharxiv

arXiv2018

Temperature dependence of the Seebeck coefficient of epitaxial $β$-Ga$_2$O$_3$ thin films

The temperature dependence of the Seebeck coefficient of homoepitaxial metal organic vapor phase (MOVPE) 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 $S_{β\text{-Ga}_2\text{O}_3\text{-Al}}=(-300\pm20)\;μ$V/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 Strattons formula. The influence of the different scattering mechanisms on the magnitude of the Seebeck coefficient is discussed and compared with Hall measurement results.

cond-mat.mtrl-sci↗

arXiv2018

Transport Properties and Finite Size Effects in $β$-Ga$_2$O$_3$ Thin Films

Thin films of the wide band gap semiconductor $β$-Ga$_2$O$_3$ 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 \mbox{(100)-orientated $β$-Ga$_2$O$_3$} films were measured as a function of temperature and film thickness. At room temperature, the electron mobilities ((115$\pm$10) $\mathrm{\frac{cm^2}{Vs}}$) 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$\pm$0.5) $\mathrm{\frac{cm^2}{Vs}}$ for a 28 nm thin film). We find that the commonly applied classical Fuchs-Sondheimer model does not explain the contribution of electron scattering at the film surfaces sufficiently. Instead, by applying an electron wave model by Bergmann, a contribution to the mobility suppression due to the large de Broglie wavelength in $β$-Ga$_2$O$_3$ is proposed as a limiting quantum mechanical size effect.

cond-mat.mtrl-sci↗