A5081471113- Ga2O3 and related materials
- GaN-based semiconductor devices and materials
- Graphene research and applications
- ZnO doping and properties
- Surface and Thin Film Phenomena
- Topological Materials and Phenomena
- Semiconductor Quantum Structures and Devices
- Quantum and electron transport phenomena
- Semiconductor materials and devices
- Advanced Chemical Physics Studies
- Molecular Junctions and Nanostructures
- Advanced Photocatalysis Techniques
- Spectroscopy and Quantum Chemical Studies
- Electronic and Structural Properties of Oxides
- Quantum Dots Synthesis And Properties
- Metal and Thin Film Mechanics
- 2D Materials and Applications
- Spectroscopy and Laser Applications
- Semiconductor materials and interfaces
- Laser-Matter Interactions and Applications
- Carbon Nanotubes in Composites
- Synthesis and Properties of Aromatic Compounds
- Optical Coatings and Gratings
- Quantum, superfluid, helium dynamics
- Chalcogenide Semiconductor Thin Films
Cornell University
2020-2024
University of Bremen
2022-2024
Max Planck Institute for Solid State Research
2024
Justus-Liebig-Universität Gießen
2022
United States Air Force Research Laboratory
2021
Interface (United States)
2021
Pennsylvania State University
2021
Chemnitz University of Technology
2017-2019
University of California, Santa Barbara
2018
Technische Universität Berlin
2008-2017
Because of its unique physical properties, graphene, a 2D honeycomb arrangement carbon atoms, has attracted tremendous attention. Silicene, the graphene equivalent for silicon, could follow this trend, opening new perspectives applications, especially due to compatibility with Si-based electronics. Silicene been theoretically predicted as buckled Si atoms and having an electronic dispersion resembling that relativistic Dirac fermions. Here we provide compelling evidence, from both structural...
The polarization of the in-plane electroluminescence (0001) orientated (In)(Al)GaN multiple quantum well light emitting diodes in ultraviolet-A and ultraviolet-B spectral range has been investigated. intensity for transverse-electric polarized relative to transverse-magnetic decreases with decreasing emission wavelength. This effect is attributed rearrangement valence bands at Γ-point Brillouin zone changing aluminum indium mole fractions wells. For shorter wavelength crystal-field split-off...
Silicene, the considered equivalent of graphene for silicon, has been recently synthesized on Ag(111) surfaces. Following tremendous success graphene, silicene might further widen horizon two-dimensional materials with new allotropes artificially created. Due to stronger spin-orbit coupling, lower group symmetry and different chemistry compared presents many interesting features. Here, we focus very important aspects layers Ag(111): First, present scanning tunneling microscopy (STM)...
The epitaxial growth and the electrical resistance of multilayer silicene on Ag(111) surface has been investigated. We show that atomic structure first layer differs from next layers adsorption Si induces formation extended terraces surrounded by step bunching. Thanks to controlled contact between tips a multiple probe scanning tunneling microscope these terraces, low sheet resistance, albeit much higher than underlying silver substrate, measured, advocating for viability silicene.
Silicene, a monolayer of silicon atoms arranged in honeycomb lattices, can be synthesized on the Ag(111) surface, where it forms several superstructures with different buckling patterns and periodicity. Using scanning tunneling microscopy (STM), we obtained high-resolution images silicene grown revealed its five phases, i.e., 4 × − α, β, β γ, some observed for first time. For each have determined atomic structure by comparing atomic-resolution STM theoretical simulation results previously...
This paper introduces a growth method—suboxide molecular-beam epitaxy (S-MBE)—which enables drastic enhancement in the rates of Ga2O3 and related materials to over 1 μm h−1 an adsorption-controlled regime, combined with excellent crystallinity. Using Ga + mixture oxygen mole fraction x(O) = 0.4 as MBE source, we overcome kinetic limits that had previously hampered by MBE. We present up 1.6 1.5 for Ga2O3/Al2O3 Ga2O3/Ga2O3 structures, respectively, very high crystalline quality at unparalleled...
We report the use of suboxide molecular-beam epitaxy (S-MBE) to grow β-Ga2O3 at a growth rate ∼1 µm/h with control silicon doping concentration from 5 × 1016 1019 cm−3. In S-MBE, pre-oxidized gallium in form molecular beam that is 99.98% Ga2O, i.e., suboxide, supplied. Directly supplying Ga2O surface bypasses rate-limiting first step two-step reaction mechanism involved by conventional MBE. As result, readily achieved relatively low temperature (Tsub ≈ 525 °C), resulting films high...
The growth of α-Ga2O3 and α-(InxGa1−x)2O3 on m-plane α-Al2O3(101̄0) by molecular beam epitaxy (MBE) metal-oxide-catalyzed (MOCATAXY) is investigated. By systematically exploring the parameter space accessed MBE MOCATAXY, phase-pure α-Ga2O3(101̄0) α-(InxGa1−x)2O3(101̄0) thin films are realized. presence In surface remarkably expands its window far into metal-rich flux regime to higher temperatures. With increasing O-to-Ga ratio (RO), incorporates up x ≤ 0.08. Upon a critical thickness,...
We report on the optoelectronic properties of Al0.25Ga0.75N/GaN-based ultraviolet (UV) photodetectors for application as a high current, gain optical switch. Due to an internal mechanism combined with conductivity two-dimensional electron gas at heterostructure interface, photocurrents in milliampere-range were obtained UV illumination. By employing mesa structure design meander geometry very low dark currents below 50 nA up bias voltage 100 V achieved. Optical switching on/off-current-ratio...
By mapping the low-energy electronic dynamics using angle resolved photoemission spectroscopy (ARPES), we have shed light on essential characteristics of (3 × 3) silicene phase Ag(111) surfaces. In particular, our results show a silicene-derived band with clear gap and linear energy-momentum dispersion near Fermi level at Γ symmetry point several distinctive Brillouin zones. Moreover, confirmed that large buckling ~0.7 Å this structure induces opening close to higher than least 0.3 eV, in...
The growth of multilayer silicene is an exciting challenge for the future silicon nano-electronics. Here, we use angle-resolved photoemission spectroscopy to map entire Brillouin zone (BZ) (√3 × √3)R30° reconstructed epitaxial islands, growing on top first (3 3) wetting layer, Ag(111) substrates. We found Λ- and V-shape linear dispersions, which relate π π* bands massless quasiparticles in silicene, at BZ centre all centres zones extended scheme, due folding Dirac cones points (1 1) BZ....
Silicene is a two‐dimensional structure composed of buckled hexagonal honeycomb lattice silicon atoms. Freestanding silicene yet to be synthesized, but epitaxial monolayers have been directly observed or predicted exist on number supporting substrates. Herein the atomic and electronic structures five distinct morphologies Ag(111) are examined through complementary techniques density functional theory soft X‐ray spectroscopy at Si L 2,3 edge. Hybridization with substrate shown cause these...
We demonstrate a marked increase in the possible growth domain and rate of O plasma-assisted molecular beam epitaxy β-(AlxGa1−x)2O3, by adding element In during growth. explain these enhancement results from metal-exchange catalytic effect. This mechanism allows us to synthesize β-(AlxGa1−x)2O3/β-Ga2O3 heterostructures at conditions that are not accessible absence In, stabilizing monoclinic β-phase. β-(AlxGa1−x)2O3 temperatures up 900 °C. Moreover, we illustrate how additional on surface...
Here, we have explored the thermal stability of α-(Al,Ga)2O3 grown by molecular-beam epitaxy on m-plane sapphire under high-temperature annealing conditions for various Al compositions (i.e., 0%, 46%, and 100%). Though uncapped α-Ga2O3 undergoes a structural phase transition to thermodynamically stable β-phase at high temperatures, find that an aluminum oxide cap atomic layer deposition preserves α-phase. Unlike α-Ga2O3, 46% 100% content remain temperatures. We quantify evolution properties...
We report controlled silicon doping of Ga2O3 grown in plasma-assisted molecular beam epitaxy. Adding an endplate to the Si effusion cell enables control mobile carrier density, leading over 5-orders magnitude change electrical resistivity. Room temperature mobilities >100 cm2/V s are achieved, with a peak value >125 at density low-1017/cm3. Temperature-dependent Hall effect measurements exhibit freeze out for samples doped below Mott criterion. A mobility 390 is observed 97 K.
Abstract The possibility to synthesize honeycomb silicene has recently been demonstrated upon providing compelling evidence through the combination of complementary experimental results and density functional theory calculations (Vogt et al 2012 Phys. Rev. Lett. 108 155501). In this case is grown on Ag(1 1 1) substrates shows a nearest neighbour distance two Si atoms ∼0.23 nm in agreement with theoretical for free-standing silicene. another publication from group authors different...
A detailed analysis based on first-principles calculations with self-energy corrections is combined photoemission spectroscopy to determine the origin of features observed in reflectance anisotropy (RAS) at semiconductor surfaces. Using $\mathrm{InP}(001)(2\ifmmode\times\else\texttimes\fi{}4)$ surface as a model case we obtain quantitative agreement between slab and low-temperature RAS measurements. We find contributions signal related either directly states or transitions perturbed bulk...
The two-dimensional silicon allotrope, silicene, could spur the development of new and original concepts in Si-based nanotechnology. Up to now silicene can only be epitaxially synthesized on a supporting substrate such as Ag(111). Even though structural electronic properties these epitaxial layers have been intensively studied, very little is known about its vibrational characteristics. Here, we present detailed study Ag(111) using situ Raman spectroscopy, which one most extensively employed...
The heteroepitaxial growth and phase formation of Ga2O3 on Al-polar AlN(0001) templates by molecular-beam epitaxy (MBE) are studied. Three different MBE approaches employed: (i) conventional MBE, (ii) suboxide (S-MBE), (iii) metal-oxide-catalyzed (MOCATAXY). We grow phase-pure β-Ga2O3(2̄01) ϵ/κ-Ga2O3(001) with smooth surfaces S-MBE MOCATAXY. Thin film analysis shows that the crystallographic surface features β-Ga2O3(2̄01)/AlN(0001) ϵ/κ-Ga2O3(001)/AlN(0001) epilayers high crystalline quality....
The InP(001)(2 x 1) surface has been reported to consist of a semiconducting monolayer buckled phosphorus dimers. This apparent violation the electron counting principle was explained by effects strong correlation. Combining first-principles calculations with reflectance anisotropy spectroscopy and LEED experiments, we find that (2 reconstruction is not at all clean surface: it induced hydrogen adsorbed in an alternating sequence on P Thus, microscopic structure InP growth plane relevant...
Silicon atoms deposited on Ag(111) produce various single layer silicene sheets with different buckling patterns and periodicities. Low temperature scanning tunneling microscopy reveals that one of the sheets, hypothetical √7 × structure, 2√3 Ag(111), is inherently highly defective displays no long-range order. Moreover, Auger photoelectron spectroscopy measurements reveal its sudden death, to end, in a dynamic fating process at ∼300 °C. This result clarifies real nature 2√3R(30°) phase thus...
We observe a catalytic mechanism during the growth of III-$\mathrm{O}$ and IV-$\mathrm{O}$ materials by suboxide molecular-beam epitaxy ($S$-MBE). By supplying molecular catalysts ${\mathrm{In}}_{2}\mathrm{O}$ SnO we increase rates ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$. This action is explained metastable adlayer $A$, which increases reaction probability reactants ${\mathrm{Ga}}_{2}\mathrm{O}$ with active atomic oxygen, leading to an derive model for binary...
We report the growth of $\alpha-Ga_2O_3$ on $m$-plane $Al_2O_3$ by conventional plasma-assisted molecular-beam epitaxy (MBE) and In-mediated metal-oxide-catalyzed (MOCATAXY). a growth-rate-diagram for (10-10), observe (i) rate increase, (ii) an expanded window, (iii) reduced out-of-lane mosaic spread when MOCATAXY is employed $\alpha-Ga_2O_3$. Through use catalysis, rates over $0.2\,\mu\text{m}\,\text{hr}^{-1}$ rocking curves with full width at half maxima $\Delta\omega \approx 0.45^{\circ}$...
Sapphire is a technologically highly relevant material, but it poses many challenges when performing epitaxial thin-film deposition. We have identified and applied the conditions for adsorption-controlled homoepitaxial growth of c-plane sapphire. The films thus grown are atomically smooth, controlled termination, outstanding crystallinity. Their chemical purity exceeds that substrates. exhibit exceptional optical properties, such as single-crystal-like bandgap low density F+ centers.
We demonstrate that the polarity of polar (0001), (0001¯) and semipolar (112¯2) InN GaN thin layers can be determined by valence band X-ray photoemission spectroscopy (XPS). The has been confirmed wet etching convergent beam electron diffraction. Unlike these two techniques, XPS is a non-destructive method unaffected surface oxidation or roughness. Different intensities states in spectra recorded using AlKα radiation are observed for N-polar group-III-polar layers. highest intensity state at...