Oliver Bierwagen
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View article: Supersaturation-Dependent Competition between β and κ Phases in the MOVPE Growth of Ga <sub>2</sub> O <sub>3</sub> on Al <sub>2</sub> O <sub>3</sub> (0001) and GaN (0001) Substrates
Supersaturation-Dependent Competition between β and κ Phases in the MOVPE Growth of Ga <sub>2</sub> O <sub>3</sub> on Al <sub>2</sub> O <sub>3</sub> (0001) and GaN (0001) Substrates Open
We present an analysis of the phase stabilization of β-Ga2O3 and κ-Ga2O3 grown by metal-organic vapor-phase epitaxy with varying supersaturation of the gas-phase precursors on c-sapphire and GaN …
View article: Advances in Gallium Oxide—from Fundamental Materials Science to Device Implementation
Advances in Gallium Oxide—from Fundamental Materials Science to Device Implementation Open
View article: Effect of lithium diffusion into Ga2O3 thin films
Effect of lithium diffusion into Ga2O3 thin films Open
View article: Assessment of Trapping Phenomena in As‐Grown and Thermally‐Treated Si‐Doped κ‐Ga<sub>2</sub>O<sub>3</sub> Layers via Optical Admittance Spectroscopy
Assessment of Trapping Phenomena in As‐Grown and Thermally‐Treated Si‐Doped κ‐Ga<sub>2</sub>O<sub>3</sub> Layers via Optical Admittance Spectroscopy Open
The impact of thermal treatments on the trapping phenomena in (001) Si‐doped κ‐Ga 2 O 3 epi‐layers, via optical admittance spectroscopy technique, is reported. Two Pt/κ‐Ga 2 O 3 Schottky contacts are investigated: one made on top of an as‐…
View article: Formation of 2D Electron Gas at a Non‐Polar Perovskite Oxide Interface: SrHfO<sub>3</sub>/BaSnO<sub>3</sub>
Formation of 2D Electron Gas at a Non‐Polar Perovskite Oxide Interface: SrHfO<sub>3</sub>/BaSnO<sub>3</sub> Open
A consistent increase in conductance in La‐doped BaSnO 3 (BLSO) is observed after forming an interface with the non‐polar perovskite SrHfO 3 (SHO). The conductance enhancement at the SHO/BLSO interface is measured as a function of the thic…
View article: Efforts to reduce the energy needed for the operation of our molecular beam epitaxy lab
Efforts to reduce the energy needed for the operation of our molecular beam epitaxy lab Open
The climate crisis and rising energy costs have motivated us to analyze the energy consumed by the operation of the molecular beam epitaxy (MBE) lab at our institute. This research lab houses 13 growth chambers for different material syste…
View article: In situ TEM study of phase transformation in oxide semiconductors
In situ TEM study of phase transformation in oxide semiconductors Open
View article: Carrier Concentration–Dependent Seebeck Coefficient in β‐Ga<sub>2</sub>O<sub>3</sub>
Carrier Concentration–Dependent Seebeck Coefficient in β‐Ga<sub>2</sub>O<sub>3</sub> Open
β‐Ga 2 O 3 is an ultrawide‐bandgap semiconductor whose thermal stability makes it a potentially interesting candidate for high‐temperature thermoelectric applications. In this work, the experimental relation between the room‐temperature (R…
View article: Unravelling the oxygen influence in cubic bixbyite In<sub>2</sub>O<sub>3</sub> on Raman active phonon modes by isotope studies
Unravelling the oxygen influence in cubic bixbyite In<sub>2</sub>O<sub>3</sub> on Raman active phonon modes by isotope studies Open
In this study, we performed comprehensive investigations on the Raman active phonon modes in cubic bixbyite In 2 O 3 , an important oxide based, wide-bandgap semiconductor. Fundamental insights into the lattice dynamics are...
View article: Kinetics, thermodynamics, and catalysis of the cation incorporation into GeO2, SnO2, and (Sn<i>x</i>Ge1−<i>x</i>)O2 during suboxide molecular beam epitaxy
Kinetics, thermodynamics, and catalysis of the cation incorporation into GeO2, SnO2, and (Sn<i>x</i>Ge1−<i>x</i>)O2 during suboxide molecular beam epitaxy Open
Rutile GeO2 is a promising ultra-wide bandgap semiconductor for future power electronic devices whose alloy with the wide bandgap semiconductor rutile-SnO2 enables bandgap engineering and the formation of heterostructure devices. The (SnxG…
View article: Effect of Lithium Diffusion into Ga2o3 Thin Films
Effect of Lithium Diffusion into Ga2o3 Thin Films Open
View article: Enabling 2D Electron Gas with High Room‐Temperature Electron Mobility Exceeding 100 cm<sup>2</sup> Vs<sup>−1</sup> at a Perovskite Oxide Interface
Enabling 2D Electron Gas with High Room‐Temperature Electron Mobility Exceeding 100 cm<sup>2</sup> Vs<sup>−1</sup> at a Perovskite Oxide Interface Open
In perovskite oxide heterostructures, bulk functional properties coexist with emergent physical phenomena at epitaxial interfaces. Notably, charge transfer at the interface between two insulating oxide layers can lead to the formation of a…
View article: Kinetics, thermodynamics, and catalysis of the cation incorporation into GeO2, SnO2, and (SnxGe1-x)O2 during suboxide molecular beam epitaxy
Kinetics, thermodynamics, and catalysis of the cation incorporation into GeO2, SnO2, and (SnxGe1-x)O2 during suboxide molecular beam epitaxy Open
Rutile GeO$_2$ is a promising ultra-wide bandgap semiconductor for future power electronic devices whose alloy with the wide bandgap semiconductor rutile-SnO$_2$ enables bandgap engineering and the formation of heterostructure devices. The…
View article: Photo-capacitance measurement in dual-frequency mode and its application to study of Pt/κ-Ga2O3 planar Schottky diode
Photo-capacitance measurement in dual-frequency mode and its application to study of Pt/κ-Ga2O3 planar Schottky diode Open
View article: Phase-selective growth of <i>κ</i>- vs <i>β</i>-Ga2O3 and (In<i>x</i>Ga1−<i>x</i>)2O3 by In-mediated metal exchange catalysis in plasma-assisted molecular beam epitaxy
Phase-selective growth of <i>κ</i>- vs <i>β</i>-Ga2O3 and (In<i>x</i>Ga1−<i>x</i>)2O3 by In-mediated metal exchange catalysis in plasma-assisted molecular beam epitaxy Open
Its large intrinsic polarization makes the metastable κ-Ga2O3 polymorph appealing for multiple applications, and the In-incorporation into both κ and β-Ga2O3 allows us to engineer their bandgap on the low-end side. In this work, we provide…
View article: Enabling two-dimensional electron gas with high room-temperature electron mobility exceeding 100 cm$^2$/Vs at a perovskite oxide interface
Enabling two-dimensional electron gas with high room-temperature electron mobility exceeding 100 cm$^2$/Vs at a perovskite oxide interface Open
In perovskite oxide heterostructures, bulk functional properties coexist with emergent physical phenomena at epitaxial interfaces. Notably, charge transfer at the interface between two insulating oxide layers can lead to the formation of a…
View article: Engineering shallow and deep level defects in κ-Ga2O3 thin films: comparing metal-organic vapour phase epitaxy to molecular beam epitaxy and the effect of annealing treatments
Engineering shallow and deep level defects in κ-Ga2O3 thin films: comparing metal-organic vapour phase epitaxy to molecular beam epitaxy and the effect of annealing treatments Open
Orthorhombic gallium oxide (κ-Ga2O3) is an ultra-wide bandgap semiconductor with great potential in new generation electronics. Its application is hindered at present by the limited physical understanding of the relat…
View article: Etching of elemental layers in oxide molecular beam epitaxy by O2-assisted formation and evaporation of their volatile (sub)oxide: The examples of Ga and Ge
Etching of elemental layers in oxide molecular beam epitaxy by O2-assisted formation and evaporation of their volatile (sub)oxide: The examples of Ga and Ge Open
The delivery of an elemental cation flux to the substrate surface in the oxide molecular beam epitaxy (MBE) chamber has been utilized not only for the epitaxial growth of oxide thin films in the presence of oxygen but also in the absence o…
View article: Molecular Beam Epitaxy of β-(In<sub><i>x</i></sub>Ga<sub>1–<i>x</i></sub>)<sub>2</sub>O<sub>3</sub>on β-Ga<sub>2</sub>O<sub>3</sub>(010): Compositional Control, Layer Quality, Anisotropic Strain Relaxation, and Prospects for Two-Dimensional Electron Gas Confinement
Molecular Beam Epitaxy of β-(In<sub><i>x</i></sub>Ga<sub>1–<i>x</i></sub>)<sub>2</sub>O<sub>3</sub>on β-Ga<sub>2</sub>O<sub>3</sub>(010): Compositional Control, Layer Quality, Anisotropic Strain Relaxation, and Prospects for Two-Dimensional Electron Gas Confinement Open
In this work, we investigate the growth of monoclinic β-(InxGa1-x)2O3 alloys on top of (010) β-Ga2O3 substrates via plasma-assisted molecular beam epitaxy. In …
View article: Etching of elemental layers in oxide molecular beam epitaxy by O2-assisted formation and evaporation of their volatile suboxide: The examples of Ga and Ge
Etching of elemental layers in oxide molecular beam epitaxy by O2-assisted formation and evaporation of their volatile suboxide: The examples of Ga and Ge Open
The delivery of an elemental cation flux to the substrate surface in the oxide molecular beam epitaxy (MBE) chamber has been utilized not only for the epitaxial growth of oxide thin films in the presence of oxygen but also in the absence o…
View article: Unraveling the atomic mechanism of the disorder–order phase transition from γ-Ga2O3 to β-Ga2O3
Unraveling the atomic mechanism of the disorder–order phase transition from γ-Ga2O3 to β-Ga2O3 Open
In this paper, we employ in situ transmission electron microscopy to study the disorder–order phase transition from amorphous Ga2O3 to γ-Ga2O3 and then to β-Ga2O3. The in situ studies are complemented by ex situ annealing experiments, of w…
View article: Phase-selective growth of $κ$- vs $β$-Ga$_2$O$_3$ and (In$_x$Ga$_{1-x}$)$_2$O$_3$ by In-mediated metal exchange catalysis in plasma-assisted molecular beam epitaxy
Phase-selective growth of $κ$- vs $β$-Ga$_2$O$_3$ and (In$_x$Ga$_{1-x}$)$_2$O$_3$ by In-mediated metal exchange catalysis in plasma-assisted molecular beam epitaxy Open
Its piezo- and potentially ferroelectric properties make the metastable kappa polymorph of Ga$_2$O$_3$ an interesting material for multiple applications, while In-incorporation into any polymorphs of Ga$_2$O$_3$ allows to lower their bandg…
View article: Interfacial Properties of the SnO/κ-Ga<sub>2</sub>O<sub>3</sub> p-n Heterojunction: A Case of Subsurface Doping Density Reduction via Thermal Treatment in κ-Ga<sub>2</sub>O<sub>3</sub>
Interfacial Properties of the SnO/κ-Ga<sub>2</sub>O<sub>3</sub> p-n Heterojunction: A Case of Subsurface Doping Density Reduction via Thermal Treatment in κ-Ga<sub>2</sub>O<sub>3</sub> Open
The interfacial properties of a planar SnO/κ-Ga2O3 p-n heterojunction have been investigated by capacitance-voltage (C-V) measurements following a methodological approach that allows consideration of sig…
View article: Underlying Mechanisms and Tunability of the Anomalous Hall Effect in NiCo<sub>2</sub>O<sub>4</sub> Films with Robust Perpendicular Magnetic Anisotropy
Underlying Mechanisms and Tunability of the Anomalous Hall Effect in NiCo<sub>2</sub>O<sub>4</sub> Films with Robust Perpendicular Magnetic Anisotropy Open
Their high tunability of electronic and magnetic properties makes transition‐metal oxides (TMOs) highly intriguing for fundamental studies and promising for a wide range of applications. TMOs with strong ferrimagnetism provide new platform…
View article: Erratum: “Drastically enhanced cation incorporation in the epitaxy of oxides due to formation and evaporation of suboxides from elemental sources” [APL Mater. 9, 111110 (2021)]
Erratum: “Drastically enhanced cation incorporation in the epitaxy of oxides due to formation and evaporation of suboxides from elemental sources” [APL Mater. 9, 111110 (2021)] Open
View article: <i>In situ</i> study and modeling of the reaction kinetics during molecular beam epitaxy of GeO2 and its etching by Ge
<i>In situ</i> study and modeling of the reaction kinetics during molecular beam epitaxy of GeO2 and its etching by Ge Open
Rutile GeO2 has been predicted to be an ultra-wide bandgap semiconductor suitable for future power electronic devices, while quartz-like GeO2 shows piezoelectric properties. To explore these crystalline phases for application and fundament…
View article: In-situ study and modeling of the reaction kinetics during molecular beam epitaxy of GeO2 and its etching by Ge
In-situ study and modeling of the reaction kinetics during molecular beam epitaxy of GeO2 and its etching by Ge Open
Rutile GeO2 has been predicted to be an ultra-wide bandgap semiconductor suitable for future power electronics devices while quartz-like GeO2 shows piezoelectric properties. To explore these crystalline phases for application and fundament…
View article: Tuning the Surface Electron Accumulation Layer of In<sub>2</sub>O<sub>3</sub> by Adsorption of Molecular Electron Donors and Acceptors
Tuning the Surface Electron Accumulation Layer of In<sub>2</sub>O<sub>3</sub> by Adsorption of Molecular Electron Donors and Acceptors Open
In 2 O 3 , an n‐type semiconducting transparent transition metal oxide, possesses a surface electron accumulation layer (SEAL) resulting from downward surface band bending due to the presence of ubiquitous oxygen vacancies. Upon annealing …
View article: Acceptor and compensating donor doping of single crystalline SnO (001) films grown by molecular beam epitaxy and its perspectives for optoelectronics and gas-sensing
Acceptor and compensating donor doping of single crystalline SnO (001) films grown by molecular beam epitaxy and its perspectives for optoelectronics and gas-sensing Open
(La and Ga)-doped tin monoxide [stannous oxide, tin (II) oxide, SnO] thin films were grown by plasma-assisted and suboxide molecular beam epitaxy with dopant concentrations ranging from ≈ 5 × 1018 to 2 × 1021 cm−3. In this concentration ra…
View article: Potential of La-Doped SrTiO<sub>3</sub> Thin Films Grown by Metal–Organic Vapor Phase Epitaxy for Thermoelectric Applications
Potential of La-Doped SrTiO<sub>3</sub> Thin Films Grown by Metal–Organic Vapor Phase Epitaxy for Thermoelectric Applications Open
La-doped SrTiO3 thin films with high structural quality were homoepitaxially grown by the metal-organic vapor phase epitaxy (MOVPE) technique. Thermogravimetric characterization of the metal-organic precursors determines suitabl…