Search

By employing a mixed SnO$_2$+Sn source, we demonstrate suboxide molecular beam epitaxy growth of phase-pure single crystalline metastable SnO(001) thin films at a growth rate of ~1.0nm/min without the need for additional oxygen. These films grow epitaxially across a wide substrate temperature range from 150 to 450{\deg}C. Hence, we present an alternative pathway to overcome the limitations of high Sn or SnO$_2$ cell temperatures and narrow growth windows encountered in previous MBE growth of metastable SnO. In-situ laser reflectometry and line-of-sight quadrupole mass spectrometry were used to investigate the rate of SnO desorption as a function of substrate temperature. While SnO ad-molecules desorption at Ts = 450{\deg}C was growth-rate limiting,the SnO films did not desorb at this temperature after growth in vacuum. The SnO (001) thin films are transparent and unintentionally p-type doped, with hole concentrations and mobilities in the range of 0.9 to 6.0x10$^{18}$cm$^{-3}$ and 2.0 to 5.5 cm$^2$/V.s, respectively. These p-type SnO films obtained at low temperatures are promising for back-end-of-line (BEOL) compatible applications and for integration with n-type oxides in p-n heterojunction and field-effect transistors, Comment: 18 pages, 10 figures

The lattice vibrations and optical properties of α-Ga2O3 are investigated by polarized Raman scattering and spectroscopic ellipsometry measurements at room temperature. Three types of epitaxial α-Ga2O3 film samples were grown on c-plane sapphire substrates by halide vapor phase epitaxy (HVPE) in three different growth modes, namely by O2-control, Ga-control, and reference mode. Seven Raman active phonons and three infrared active phonons are determined experimentally for all samples. The relative intensities of Eg(2), Eg(4), and Eg(5) modes in Z(XY)Z Raman spectra varies as a function of growth mode. The growth mode has no obvious effect on the infrared active Eu(2) and Eu(4) modes, while phonon lifetime of the Eu(3) mode drastically changes. For the Eu(3) mode, the O2-control sample exhibits a significantly reduced broadening factor of 7.6 cm-1 compared with that of the reference (10 cm-1), and the Ga-control (16.6 cm-1) samples. All the three types of samples show similar complex ordinary dielectric functions in the spectral range between 0.5 and 6.5 eV indicating no obvious changes within the band structure by changing the growth mode.