Heterostructure growth, electrical transport and electronic structure of crystalline Dirac nodal arc semimetal PtSn.

Topological semimetals have recently garnered widespread interest in the quantum materials research community due to their symmetry-protected surface states with dissipationless transport which have potential applications in next-generation low-power electronic devices. One such material, [Formula: see text], exhibits Dirac nodal arcs and although the topological properties of single crystals have been investigated, there have been no reports in crystalline thin film geometry. We examined the growth of [Formula: see text] heterostructures on a range of single crystals by optimizing the electron beam evaporation of Pt and Sn and studied the effect of vacuum thermal annealing on phase and crystallinity.

Synthesis, Structure, and Properties of CuBiSeCl: A Chalcohalide Material with Low Thermal Conductivity.

Mixed anion halide-chalcogenide materials have recently attracted attention for a variety of applications, owing to their desirable optoelectronic properties. We report the synthesis of a previously unreported mixed-metal chalcohalide material, CuBiSeCl (), accessed through a simple, low-temperature solid-state route. The physical structure is characterized through single-crystal X-ray diffraction and reveals significant Cu displacement within the CuSeCl octahedra.

Looking Outside the Square: The Growth, Structure, and Resilient Two-Dimensional Surface Electron Gas of Square SnO Nanotubes.

Nanotechnology has delivered an amazing range of new materials such as nanowires, tubes, ribbons, belts, cages, flowers, and sheets. However, these are usually circular, cylindrical, or hexagonal in nature, while nanostructures with square geometries are comparatively rare. Here, a highly scalable method is reported for producing vertically aligned Sb-doped SnO nanotubes with perfectly-square geometries on Au nanoparticle covered m-plane sapphire using mist chemical vapor deposition.

Band Alignments, Electronic Structure, and Core-Level Spectra of Bulk Molybdenum Dichalcogenides (MoS, MoSe, and MoTe).

A comprehensive study of bulk molybdenum dichalcogenides is presented with the use of soft and hard X-ray photoelectron (SXPS and HAXPES) spectroscopy combined with hybrid density functional theory (DFT). The main core levels of MoS, MoSe, and MoTe are explored. Laboratory-based X-ray photoelectron spectroscopy (XPS) is used to determine the ionization potential (IP) values of the MoX series as 5.

Computational Prediction and Experimental Realization of Earth-Abundant Transparent Conducting Oxide Ga-Doped ZnSbO.

Transparent conducting oxides have become ubiquitous in modern optoelectronics. However, the number of oxides that are transparent to visible light and have the metallic-like conductivity necessary for applications is limited to a handful of systems that have been known for the past 40 years. In this work, we use hybrid density functional theory and defect chemistry analysis to demonstrate that tri-rutile zinc antimonate, ZnSbO, is an ideal transparent conducting oxide and to identify gallium as the optimal dopant to yield high conductivity and transparency.

Long-Life and pH-Stable SnO-Coated Au Nanoparticles for SHINERS.

Shell-isolated nanoparticles (SHINs) with a 37 nm gold core and an 11 nm tin dioxide (SnO) coating exhibited long-life Raman enhancement for 3 months and a wide pH stability of pH 2-13 in comparison with conventional SiO-coated SHINs. Herein, Au-SnO is demonstrated as a more durable SHIN for use in the technique Shell-Isolated Nanoparticles for Enhanced Raman Spectroscopy (SHINERS).

Tackling Disorder in γ-Ga O.

Ga O and its polymorphs are attracting increasing attention. The rich structural space of polymorphic oxide systems such as Ga O offers potential for electronic structure engineering, which is of particular interest for a range of applications, such as power electronics. γ-Ga O presents a particular challenge across synthesis, characterization, and theory due to its inherent disorder and resulting complex structure-electronic-structure relationship.

GeSe photovoltaics: doping, interfacial layer and devices.

Germanium selenide (GeSe) bulk crystals, thin films and solar cells are investigated with a focus on acceptor-doping with silver (Ag) and the use of an SbSe interfacial layer. The Ag-doping of GeSe occurred by a stoichiometric melt growth technique that created Ag-doped GeSe bulk crystals. A combination of capacitance voltage measurements, synchrotron radiation photoemission spectroscopy and surface space-charge calculations indicates that Ag-doping increases the hole density from 5.

Indium Gallium Oxide Alloys: Electronic Structure, Optical Gap, Surface Space Charge, and Chemical Trends within Common-Cation Semiconductors.

The electronic and optical properties of (InGa)O alloys are highly tunable, giving rise to a myriad of applications including transparent conductors, transparent electronics, and solar-blind ultraviolet photodetectors. Here, we investigate these properties for a high quality pulsed laser deposited film which possesses a lateral cation composition gradient (0.01 ≤ ≤ 0.

How Oxygen Exposure Improves the Back Contact and Performance of Antimony Selenide Solar Cells.

The improvement of antimony selenide solar cells by short-term air exposure is explained using complementary cell and material studies. We demonstrate that exposure to air yields a relative efficiency improvement of n-type SbSe solar cells of ca. 10% by oxidation of the back surface and a reduction in the back contact barrier height (measured by ) from 320 to 280 meV.

Vacancy-Ordered Double Perovskite CsTeI Thin Films for Optoelectronics.

Alternatives to lead- and tin-based perovskites for photovoltaics and optoelectronics are sought that do not suffer from the disadvantages of toxicity and low device efficiency of present-day materials. Here we report a study of the double perovskite CsTeI, which we have synthesized in the thin film form for the first time. Exhaustive trials concluded that spin coating CsI and TeI using an antisolvent method produced uniform films, confirmed as CsTeI by XRD with Rietveld analysis.

GeSe: Optical Spectroscopy and Theoretical Study of a van der Waals Solar Absorber.

The van der Waals material GeSe is a potential solar absorber, but its optoelectronic properties are not yet fully understood. Here, through a combined theoretical and experimental approach, the optoelectronic and structural properties of GeSe are determined. A fundamental absorption onset of 1.

Resonant Ta Doping for Enhanced Mobility in Transparent Conducting SnO.

Transparent conducting oxides (TCOs) are ubiquitous in modern consumer electronics. SnO is an earth abundant, cheaper alternative to InO as a TCO. However, its performance in terms of mobilities and conductivities lags behind that of InO.

Band Alignments, Band Gap, Core Levels, and Valence Band States in CuBiS for Photovoltaics.

The earth-abundant semiconductor CuBiS (CBS) exhibits promising photovoltaic properties and is often considered analogous to the solar absorbers copper indium gallium diselenide (CIGS) and copper zinc tin sulfide (CZTS) despite few device reports. The extent to which this is justifiable is explored via a thorough X-ray photoemission spectroscopy (XPS) analysis: spanning core levels, ionization potential, work function, surface contamination, cleaning, band alignment, and valence-band density of states. The XPS analysis overcomes and addresses the shortcomings of prior XPS studies of this material.

Core Levels, Band Alignments, and Valence-Band States in CuSbS for Solar Cell Applications.

The earth-abundant material CuSbS (CAS) has shown good optical properties as a photovoltaic solar absorber material, but has seen relatively poor solar cell performance. To investigate the reason for this anomaly, the core levels of the constituent elements, surface contaminants, ionization potential, and valence-band spectra are studied by X-ray photoemission spectroscopy. The ionization potential and electron affinity for this material (4.

Optimization of self-catalyzed InAs Nanowires on flexible graphite for photovoltaic infrared photodetectors.

The recent discovery of flexible graphene monolayers has triggered extensive research interest for the development of III-V/graphene functional hybrid heterostructures. In order to fully exploit their enormous potential in device applications, it is essential to optimize epitaxial growth for the precise control of nanowire geometry and density. Herein, we present a comprehensive growth study of InAs nanowires on graphitic substrates by molecular beam epitaxy.

Direct Measurements of Fermi Level Pinning at the Surface of Intrinsically n-Type InGaAs Nanowires.

Surface effects strongly dominate the intrinsic properties of semiconductor nanowires (NWs), an observation that is commonly attributed to the presence of surface states and their modification of the electronic band structure. Although the effects of the exposed, bare NW surface have been widely studied with respect to charge carrier transport and optical properties, the underlying electronic band structure, Fermi level pinning, and surface band bending profiles are not well explored. Here, we directly and quantitatively assess the Fermi level pinning at the surfaces of composition-tunable, intrinsically n-type InGaAs NWs, as one of the prominent, technologically most relevant NW systems, by using correlated photoluminescence (PL) and X-ray photoemission spectroscopy (XPS).

Realization of Vertically Aligned, Ultrahigh Aspect Ratio InAsSb Nanowires on Graphite.

The monolithic integration of InAs(1-x)Sb(x) semiconductor nanowires on graphitic substrates holds enormous promise for cost-effective, high-performance, and flexible devices in optoelectronics and high-speed electronics. However, the growth of InAs(1-x)Sb(x) nanowires with high aspect ratio essential for device applications is extremely challenging due to Sb-induced suppression of axial growth and enhancement in radial growth. We report the realization of high quality, vertically aligned, nontapered and ultrahigh aspect ratio InAs(1-x)Sb(x) nanowires with Sb composition (xSb(%)) up to ∼12% grown by indium-droplet assisted molecular beam epitaxy on graphite substrate.

Sb-induced phase control of InAsSb nanowires grown by molecular beam epitaxy.

For the first time, we report a complete control of crystal structure in InAs(1-x)Sb(x) NWs by tuning the antimony (Sb) composition. This claim is substantiated by high-resolution transmission electron microscopy combined with photoluminescence spectroscopy. The pure InAs nanowires generally show a mixture of wurtzite (WZ) and zinc-blende (ZB) phases, where addition of a small amount of Sb (∼2-4%) led to quasi-pure WZ InAsSb NWs, while further increase of Sb (∼10%) resulted in quasi-pure ZB InAsSb NWs.

Graphitic platform for self-catalysed InAs nanowires growth by molecular beam epitaxy.

We report the self-catalysed growth of InAs nanowires (NWs) on graphite thin films using molecular beam epitaxy via a droplet-assisted technique. Through optimising metal droplets, we obtained vertically aligned InAs NWs with highly uniform diameter along their entire length. In comparison with conventional InAs NWs grown on Si (111), the graphite surface led to significant effects on the NWs geometry grown on it, i.

Giant reduction of InN surface electron accumulation: compensation of surface donors by Mg dopants.

Extreme electron accumulation with sheet density greater than 10(13) cm(-2) is almost universally present at the surface of indium nitride (InN). Here, x-ray photoemission spectroscopy and secondary ion mass spectrometry are used to show that the surface Fermi level decreases as the Mg concentration increases, with the sheet electron density falling to below 10(8) cm(-2). Surface space-charge calculations indicate that the lowering of the surface Fermi level increases the density of unoccupied donor-type surface states and that these are largely compensated by Mg acceptors in the near-surface hole depletion region rather than by accumulated electrons.

Conductivity in transparent oxide semiconductors.

Despite an extensive research effort for over 60 years, an understanding of the origins of conductivity in wide band gap transparent conducting oxide (TCO) semiconductors remains elusive. While TCOs have already found widespread use in device applications requiring a transparent contact, there are currently enormous efforts to (i) increase the conductivity of existing materials, (ii) identify suitable alternatives, and (iii) attempt to gain semiconductor-engineering levels of control over their carrier density, essential for the incorporation of TCOs into a new generation of multifunctional transparent electronic devices. These efforts, however, are dependent on a microscopic identification of the defects and impurities leading to the high unintentional carrier densities present in these materials.

Thickness dependence of the strain, band gap and transport properties of epitaxial In2O3 thin films grown on Y-stabilised ZrO2(111).

Epitaxial films of In(2)O(3) have been grown on Y-stabilised ZrO(2)(111) substrates by molecular beam epitaxy over a range of thicknesses between 35 and 420 nm. The thinnest films are strained, but display a 'cross-hatch' morphology associated with a network of misfit dislocations which allow partial accommodation of the lattice mismatch. With increasing thickness a 'dewetting' process occurs and the films break up into micron sized mesas, which coalesce into continuous films at the highest coverages.

Surface band-gap narrowing in quantized electron accumulation layers.

An energy gap between the valence and the conduction band is the defining property of a semiconductor, and the gap size plays a crucial role in the design of semiconductor devices. We show that the presence of a two-dimensional electron gas near to the surface of a semiconductor can significantly alter the size of its band gap through many-body effects caused by its high electron density, resulting in a surface band gap that is much smaller than that in the bulk. Apart from reconciling a number of disparate previous experimental findings, the results suggest an entirely new route to spatially inhomogeneous band-gap engineering.

Unintentional conductivity of indium nitride: transport modelling and microscopic origins.

A three-region model for the high n-type conductivity in InN, including contributions from the bulk, surface and buffer layer interface of the sample, is considered. In particular, a parallel conduction analysis is used to show that this model can account for the carrier concentration and mobility variation with film thickness that has previously been determined from single-field Hall effect measurements. Microscopic origins for the donors in each region are considered, and the overriding tendency towards n-type conductivity is discussed in terms of the bulk band structure of InN.