The epitaxial growth of functional oxides using a substrate with a graphene layer is a highly desirable method for improving structural quality and obtaining freestanding epitaxial nanomembranes for scientific study, applications, and economical reuse of substrates. However, the aggressive oxidizing conditions typically used in growing epitaxial oxides can damage graphene. Here, we demonstrate the successful use of hybrid molecular beam epitaxy for SrTiO
3
growth that does not require an independent oxygen source, thus avoiding graphene damage. This approach produces epitaxial films with self-regulating cation stoichiometry. Furthermore, the film (46-nm-thick SrTiO
3
) can be exfoliated and transferred to foreign substrates. These results open the door to future studies of previously unattainable freestanding oxide nanomembranes grown in an adsorption-controlled manner by hybrid molecular beam epitaxy. This approach has potentially important implications for the commercial application of perovskite oxides in flexible electronics and as a dielectric in van der Waals thin-film electronics.
SrSnO3 (SSO) is an emerging
ultrawide band gap (UWBG)
semiconductor with potential in high-power applications. In-plane
compressive strain was recently shown to stabilize the high-temperature
tetragonal phase of SSO at room temperature (RT), which exists at T ≥ 1062 K in bulk. Here, we report on the study
of strain relaxation in the epitaxial, tetragonal phase of Nd-doped
SSO films grown on GdScO3 (110) (GSO) substrates and how
it influences the electronic transport properties. The thinnest SSO
film (thickness, t = 12 nm) yielded a fully coherent
tetragonal phase at RT. At 12 nm < t < 110
nm, the tetragonal phase first transformed into the orthorhombic phase,
and then at t ≥ 110 nm, the orthorhombic phase
began to relax by forming misfit dislocations. Remarkably, the tetragonal
phase remained fully coherent until it completely transformed into
the orthorhombic phase. A significant increase in mobility from 14
to 73 cm2 V–1 s–1 was
discovered between 12 and 330 nm. Using thickness- and temperature-dependent
electronic transport measurements, we discuss the important roles
of the surface, phase coexistence, and misfit dislocations on carrier
density and mobility in Nd-doped SSO. This study provides unprecedented
insight into the effect of thickness and strain relaxation behavior
and their consequences for electronic transport in doped SSO with
implications for high-power electronic devices.
The discovery and development of ultra-wide bandgap (UWBG) semiconductors is crucial to accelerate the adoption of renewable power sources. This necessitates an UWBG semiconductor that exhibits robust doping with high carrier mobility over a wide range of carrier concentrations. Here we demonstrate that epitaxial thin films of the perovskite oxide NdxSr1−xSnO3 (SSO) do exactly this. Nd is used as a donor to successfully modulate the carrier concentration over nearly two orders of magnitude, from 3.7 × 1018 cm−3 to 2.0 × 1020 cm−3. Despite being grown on lattice-mismatched substrates and thus having relatively high structural disorder, SSO films exhibited the highest room-temperature mobility, ~70 cm2 V−1 s−1, among all known UWBG semiconductors in the range of carrier concentrations studied. The phonon-limited mobility is calculated from first principles and supplemented with a model to treat ionized impurity and Kondo scattering. This produces excellent agreement with experiment over a wide range of temperatures and carrier concentrations, and predicts the room-temperature phonon-limited mobility to be 76–99 cm2 V−1 s−1 depending on carrier concentration. This work establishes a perovskite oxide as an emerging UWBG semiconductor candidate with potential for applications in power electronics.
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