arXiv subjects

Elias Kluth

Publications and source records attributed to Elias Kluth.

3 recordsLinked to original sources

arXiv2022

Epitaxial synthesis of unintentionally doped p-type SnO (001) via suboxide molecular beam epitaxy

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°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°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

cond-mat.mtrl-sci↗

arXiv2022

Tackling Disorder in $γ$-Ga$_2$O$_3$

Ga$_2$O$_3$ and its polymorphs are attracting increasing attention. The rich structural space of polymorphic oxide systems such as Ga$_2$O$_3$ offers potential for electronic structure engineering, which is of particular interest for a range of applications, such as power electronics. $γ$-Ga$_2$O$_3$ presents a particular challenge across synthesis, characterisation, and theory due to its inherent disorder and resulting complex structure -- electronic structure relationship. Here, density functional theory is used in combination with a machine learning approach to screen nearly one million potential structures, thereby developing a robust atomistic model of the $γ$-phase. Theoretical results are compared with surface and bulk sensitive soft and hard X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, spectroscopic ellipsometry, and photoluminescence excitation spectroscopy experiments representative of the occupied and unoccupied states of $γ$-Ga$_2$O$_3$. The first onset of strong absorption at room temperature is found at 5.1 eV from spectroscopic ellipsometry, which agrees well with the excitation maximum at 5.17 eV obtained by PLE spectroscopy, where the latter shifts to 5.33 eV at 5 K. This work presents a leap forward in the treatment of complex, disordered oxides and is a crucial step towards exploring how their electronic structure can be understood in terms of local coordination and overall structure.

cond-mat.mtrl-sci↗

arXiv2021

Molecular beam epitaxy of single-crystalline bixbyite (In$_{1-x}$Ga$_x$)$_2$O$_3$ films ($x \leq 0.18$): Structural properties and consequences of compositional inhomogeneity

In this work, we show the heteroepitaxial growth of single-crystalline bixbyite (In$_{1-x}$Ga$_x$)$_2$O$_3$ films on (111)-oriented yttria-stabilized zirconia substrates using plasma-assisted molecular beam epitaxy under various growth conditions. A pure In$_2$O$_3$ buffer layer between the substrate and (In$_{1-x}$Ga$_x$)$_2$O$_3$ alloy is shown to result in smoother film surfaces and significantly improved crystallinity. Symmetric out-of-plane 2$θ- ω$ x-ray diffraction scans show a single (111) crystal orientation and transmission electron microscopy confirms the single-crystallinity up to $x = 0.18$ and only slight film quality deterioration with increasing Ga content. Partially relaxed layers are demonstrated via reciprocal space mapping with lattice parameters fitting well to Vegard's law. However, the Ga cations are not evenly distributed within the films containing nominally $x > 0.11$: inclusions with high Ga density up to $x = 0.50$ are observed within a "matrix" with $x \approx 0.08$. The cubic bixbyite phase is preserved, in both the "matrix" and the inclusions. Moreover, for $x \geq 0.11$, both the Raman phonon lines as well as the optical absorption onset remain nearly constant. Hard x-ray photoelectron spectroscopy measurements also indicate a widening of the band gap and exhibit similar saturation of the Ga 2p core level position for high Ga contents. This saturation behavior of the spectroscopic properties further supports the limited Ga incorporation into the "matrix" of the film.

cond-mat.mtrl-sci↗