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Undoped, Al-doped and Al-B co-doped ZnO transparent semiconductor thin films were deposited on glass substrates by sol-gel method and spin coating technique. This study investigated the influence of Al (2 at.%) doping and Al (2 at.%)-B (1 or 2 at.%) co-doping on the microstructural, surface morphological, electrical and optical properties of the ZnO-based thin films. XRD analysis indicated that all as-prepared ZnO-based thin films were polycrystalline with a single-phase hexagonal wurtzite structure. The substitution of extrinsic dopants (Al or Al-B) into ZnO thin films can significantly degrade the crystallinity, refine the microstructures, improve surface flatness, enhance the optical transparency in the visible spectrum and lead to a shift in the absorption edge toward the short-wavelength direction. Experimental results showed that the Al-doped and Al-B co-doped ZnO thin films exhibited high average transmittance (&gt, 91.3%) and low average reflectance (&lt, 10%) in the visible region compared with the ZnO thin film. The optical parameters, including the optical bandgap, Urbach energy, extinction coefficient and refractive index, changed with the extrinsic doping level. Measured results of electrical properties revealed that the singly doped and co-doped samples exhibited higher electron concentrations and lower resistivities than those of the undoped sample and suggested that 2 at.% Al and 1 at.% B were the optimum dopant concentrations for achieving the best electrical properties in this study.

Antimonene is a promising two-dimensional (2D) material that is calculated to have a significant fundamental bandgap usable for advanced applications such as field-effect transistors, photoelectric devices, and the quantum-spin Hall (QSH) state. Herein, we demonstrate a phenomenon termed topological proximity effect, which occurs between a 2D material and a three-dimensional (3D) topological insulator (TI). We provide strong evidence derived from hydrogen etching on Sb2Te3 that large-area and well-ordered antimonene presents a 2D topological state. Delicate analysis with a scanning tunneling microscope of the evolutionary intermediates reveals that hydrogen etching on Sb2Te3 resulted in the formation of a large area of antimonene with a buckled structure. A topological state formed in the antimonene/Sb2Te3 heterostructure was confirmed with angle-resolved photoemission spectra and density-functional theory calculations; in particular, the Dirac point was located almost at the Fermi level. The results reveal that Dirac fermions are indeed realized at the interface of a 2D normal insulator (NI) and a 3D TI as a result of strong hybridization between antimonene and Sb2Te3. Our work demonstrates that the position of the Dirac point and the shape of the Dirac surface state can be tuned by varying the energy position of the NI valence band, which modifies the direction of the spin texture of Sb-BL/Sb2Te3via varying the Fermi level. This topological phase in 2D-material engineering has generated a paradigm in that the topological proximity effect at the NI/TI interface has been realized, which demonstrates a way to create QSH systems in 2D-material TI heterostructures.

A record high zT of 2.2 at 740 K is reported in Ge0.92Sb0.08Te single crystals, with an optimal hole carrier concentration ≈4 × 1020 cm−3 that simultaneously maximizes the power factor (PF) ≈56 µW cm−1 K−2 and minimizes the thermal conductivity ≈1.9 Wm−1 K−1. In addition to the presence of herringbone domains and stacking faults, the Ge0.92Sb0.08Te exhibits significant modification to phonon dispersion with an extra phonon excitation around ≈5–6 meV at Γ point of the Brillouin zone as confirmed through inelastic neutron scattering (INS) measurements. Density functional theory (DFT) confirmed this phonon excitation, and predicted another higher energy phonon excitation ≈12–13 meV at W point. These phonon excitations collectively increase the number of phonon decay channels leading to softening of phonon frequencies such that a three‐phonon process is dominant in Ge0.92Sb0.08Te, in contrast to a dominant four‐phonon process in pristine GeTe, highlighting the importance of phonon engineering approaches to improving thermoelectric (TE) performance., The origin of high zT ≈ 2.2 at 740 K of Ge0.92Sb0.08Te is uncovered via DFT and inelastic neutron scattering measurements that reveal the presence of a new phonon band at a transfer energy E ≈5–6 meV, highlighting the importance of phonon engineering approaches to improving thermoelectricperformance.

In this work, a high thermoelectric figure of merit, zT of 1.9 at 740 K is achieved in Ge1−xBixTe crystals through the concurrent of Seebeck coefficient enhancement and thermal conductivity reduction with Bi dopants. The substitution of Bi for Ge not only compensates the superfluous hole carriers in pristine GeTe but also shifts the Fermi level (EF) to an eligible region. Experimentally, with moderate 6–10% Bi dopants, the carrier concentration is drastically decreased from 8.7 × 1020 cm−3 to 3–5 × 1020 cm−3 and the Seebeck coefficient is boosted three times to 75 μVK−1. In the meantime, based on the density functional theory (DFT) calculation, the Fermi level EF starts to intersect with the pudding mold band at L point, where the band effective mass is enhanced. The enhanced Seebeck coefficient effectively compensates the decrease of electrical conductivity and thus successfully maintain the power factor as large as or even superior than that of the pristine GeTe. In addition, the Bi doping significantly reduces both thermal conductivities of carriers and lattices to an extremely low limit of 1.57 W m−1K−1 at 740 K with 10% Bi dopants, which is an about 63% reduction as compared with that of pristine GeTe. The elevated figure of merit observed in Ge1−xBixTe specimens is therefore realized by synergistically optimizing the power factor and downgrading the thermal conductivity of alloying effect and lattice anharmonicity caused by Bi doping.

A photocurrent was applied to a Sb2SeTe2 topological insulator nanosheet at a wavelength of 325 nm, and it exhibited extremely high performance such that the responsivity and photoconductive gain are 354 A W−1 and 1531, respectively, at a bias of 0.1 V. This photoresponse is orders of magnitude higher than most reported values for topological insulators and two-dimensional transitional metal dichalcogenides. The photoresponse is linear with the applied voltage. Responsivity and gain under vacuum are higher than that in air by a factor of 2.5. This finding suggests that the Sb2SeTe2 topological insulator nanosheet has great potential for ultraviolet optoelectronic device applications.

A record high zT of 2.2 at 740 K is reported in Ge0.92Sb0.08Te single crystals, with an optimal hole carrier concentration ≈4 × 1020 cm-3 that simultaneously maximizes the power factor (PF) ≈56 µW cm-1 K-2 and minimizes the thermal conductivity ≈1.9 Wm-1 K-1. In addition to the presence of herringbone domains and stacking faults, the Ge0.92Sb0.08Te exhibits significant modification to phonon dispersion with an extra phonon excitation around ≈5-6 meV at Γ point of the Brillouin zone as confirmed through inelastic neutron scattering (INS) measurements. Density functional theory (DFT) confirmed this phonon excitation, and predicted another higher energy phonon excitation ≈12-13 meV at W point. These phonon excitations collectively increase the number of phonon decay channels leading to softening of phonon frequencies such that a three-phonon process is dominant in Ge0.92Sb0.08Te, in contrast to a dominant four-phonon process in pristine GeTe, highlighting the importance of phonon engineering approaches to improving thermoelectric (TE) performance.

In this work, a high thermoelectric figure of merit, zT of 1.9 at 740 K is achieved in Ge1−xBixTe crystals through the concurrent of Seebeck coefficient enhancement and thermal conductivity reduction with Bi dopants. The substitution of Bi for Ge not only compensates the superfluous hole carriers in pristine GeTe but also shifts the Fermi level (EF) to an eligible region. Experimentally, with moderate 6–10% Bi dopants, the carrier concentration is drastically decreased from 8.7 × 1020 cm−3 to 3–5 × 1020 cm−3 and the Seebeck coefficient is boosted three times to 75 μVK−1. In the meantime, based on the density functional theory (DFT) calculation, the Fermi level EF starts to intersect with the pudding mold band at L point, where the band effective mass is enhanced. The enhanced Seebeck coefficient effectively compensates the decrease of electrical conductivity and thus successfully maintain the power factor as large as or even superior than that of the pristine GeTe. In addition, the Bi doping significantly reduces both thermal conductivities of carriers and lattices to an extremely low limit of 1.57 W m−1K−1 at 740 K with 10% Bi dopants, which is an about 63% reduction as compared with that of pristine GeTe. The elevated figure of merit observed in Ge1−xBixTe specimens is therefore realized by synergistically optimizing the power factor and downgrading the thermal conductivity of alloying effect and lattice anharmonicity caused by Bi doping.

The electric and optical properties were studied in Sb2Te3 with different thickness. It reveals the same resistivity at measured temperatures, but shows a larger magnetoresistance ratio at thicker flakes. All measured data conformed to a linear correlation between magnetoresistance ratio which is one-order enhanced, and mobility over a wide mobility range. A higher photocurrent response is observed in thicker flakes. These results support that the thickness enhances the effective carrier mobility which leads to magneto-transport and optic properties enhancement.

High-quality ZnO films have been reproducibly grown on a LiGaO2 substrate by chemical vapor deposition with optimized growth parameters. The in-plane epitaxial relationship of ZnO[100]//LiGaO2[100] is revealed by transmission electron microscopy (TEM). The surface morphology of as-grown ZnO films characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrates a very smooth surface with a root-mean-square roughness of 0.6 nm. The full width at half maximum value (FWHM) of 0.03° for the (0002) X-ray rocking curve shows the excellent crystalline quality of as-grown ZnO films. High transparency of the ZnO films in the visible range was revealed by optical transmittance measurements. The strong near-band-edge UV emission accompanied by a negligible defect-related green band emission suggests that the as-grown ZnO films have a high optical quality. Microstructural properties and strain state of the samples were also studied by TEM, X-ray diffraction (XRD) reciprocal space maps and Raman scattering analysis. Substrate compliant deformation, confirmed by the high-resolution TEM analysis, is suggested to be beneficial to decrease the compressive strain in the epilayer and increase the quality of the ZnO. This facile growth process towards high-quality ZnO opens up a broad potential application of high-efficiency ZnO-based devices on a LiGaO2 substrate.

The photocurrent was performed in the Sb2SeTe2 topological insulator at a wavelength of 532 nm. It exhibits extremely high performance that the responsivity and the photoconductive gain reach 2293 AW−1 and 5344 at 1 V. This high photoresponse is orders of magnitude higher than most reported values in topological insulators and two-dimensional transitional metal dichalcogenides. This finding suggests that the Sb2SeTe2 nanoflake has great potential for future optoelectronic device applications.

LiGaO 2 single crystal, a promising substrate for GaN and ZnO epitaxial growth, has been grown by theCzochralski method. X-ray diffraction, atomic force microscopy, micro-Raman, DUV –visible NIR, photo-luminescence and cathodoluminescence were used to characterize as-grown LiGaO 2 single crystals. Thepolished LiGaO 2 substrates displayed improved surface morphology with inconspicuous surfacescratches. The optical band gap energy of the LiGaO 2 single crystal was found to be 5.26 eV. Thecathodoluminescence spectrum of the LiGaO 2 single crystal exhibited strong UV emission, accompaniedby weak, green–yellow emission.& 2014 Elsevier B.V. All rights reserved. 1. IntroductionWurtzite-like structured β -LiGaO 2 (LGO) has attracted greatinterest in recent years due to the fact that it is the most closelylattice-matched substrate currently being considered for GaNheteroepitaxy, which offers distinct advantages toward growth ofhigh quality GaN [1,2]. It is also a promising lattice-matchedsubstrate for heteroepitaxy of ZnO and InN [3,4]. LGO is orthor-hombic with space group Pna2

Ga-doped ZnO (GZO), B–Ga codoped ZnO (GZO:B), and Al–Ga codoped ZnO (GZO:Al) transparent semiconductor thin films and photoconductive ultraviolet (UV) detectors were fabricated on alkali-free glass substrates by the sol–gel route. The doping concentration of Ga was 0.5 at.%, and that of Ga plus B or Al was 1 at.% in the precursor solutions. The structural, electrical, and optical properties of GZO, GZO:B and GZO:Al thin films were compared and the photoconductivity and photoresponsivity of ZnO-based UV photodetectors are reported. All as-prepared ZnO-based thin films had high transparency in the visible region, and the GZO:Al thin film exhibited the best electrical properties. Current–voltage (I–V) characteristics in dark and illuminated conditions showed that the resistance of the films fell by more than an order of magnitude upon UV light illumination. In this study, we found that the photoconductive UV detector based on GZO:Al film exhibited the highest responsivity, 3.22 A/W at 5 V bias under UV light illumination.

The photocurrent was performed in the Sb2SeTe2 topological insulator at a wavelength of 532 nm. It exhibits extremely high performance that the responsivity and the photoconductive gain reach 2293 AW−1 and 5344 at 1 V. This high photoresponse is orders of magnitude higher than most reported values in topological insulators and two-dimensional transitional metal dichalcogenides. This finding suggests that the Sb2SeTe2 nanoflake has great potential for future optoelectronic device applications.

A topological insulator (TI) is a quantum material in a new class with attractive properties for physical and technological applications. Here we derive the electronic structure of highly crystalline Sb2Te2Se single crystals studied with angle-resolved photoemission spectra. The result of band mapping reveals that the Sb2Te2Se compound behaves as a p-type semiconductor and has an isolated Dirac cone of a topological surface state, which is highly favored for spintronic and thermoelectric devices because of the dissipation-less surface state and the decreased scattering from bulk bands. More importantly, the topological surface state and doping level in Sb2Te2Se are difficult to alter for a cleaved surface exposed to air; the robustness of the topological surface state defined in our data indicates that this Sb2Te2Se compound has a great potential for future atmospheric applications.

A topological insulator (TI) is a quantum material in a new class with attractive properties for physical and technological applications. Here we derive the electronic structure of highly crystalline Sb2Te2Se single crystals studied with angle-resolved photoemission spectra. The result of band mapping reveals that the Sb2Te2Se compound behaves as a p-type semiconductor and has an isolated Dirac cone of a topological surface state, which is highly favored for spintronic and thermoelectric devices because of the dissipation-less surface state and the decreased scattering from bulk bands. More importantly, the topological surface state and doping level in Sb2Te2Se are difficult to alter for a cleaved surface exposed to air; the robustness of the topological surface state defined in our data indicates that this Sb2Te2Se compound has a great potential for future atmospheric applications.

We report the Aharonov-Bohm (AB) oscillation in the BiSbTe3 topological insulator macroflake. The magnetoresistance reveals periodic oscillations. The oscillation index number reveals the Berry phase is π which supports the oscillation originates from the surface state. The AB oscillation frequency increases as temperature decreases, and the corresponding phase coherence length is consistent with that extracted from the weak antilocalization. The phase coherence length is proportional to T−1∕2. The magnetoresistance ratio reaches 700% (1000%) at 9 T (14 T) and 2 K, and it is proportional to the carrier mobility. The magnetoresistance ratio is larger than all reported values in (Bi, Sb)2(Te, Se)3 topological insulators.

The robustness of Sb2SeTe2 topological insulators against surface oxidation has been comparatively investigated through their magneto-transport and X-ray photoelectron spectroscopic properties with samples freshly cleaved or exposed to air over various timeframes. The magnetoresistance data exhibit Shubnikov-de Haas oscillations with the same period of oscillations for all samples regardless of surface oxidation, whereas the core-level electron binding energies of the constituent elements vary. That there is no shift in Fermi levels and no smearing-out in the amplitude of oscillations suggests that the surface states of the studied topological insulators are impervious to surface oxidation.

A non-saturating linear magnetoresistance (MR) is observed in Cu0.1Bi2Se3 in a wide range of temperatures. The crossover magnetic field, B*, deviating from the linear MR, increases as the temperature increases. The experimental results show that the normalized B*, inverse MR slope and mobility follow the same temperature dependence that is consistent with the model constructed by Parich and Littlewood (PL model). The mechanism of the T 2 dependent B* is systematically and comprehensively discussed through existing theories, and might be due to the electron−electron scattering in a highly uniform system with a few low mobility defects.

A topological insulating Bi2Te3 single crystal was successfully grown with good uniformity using a home-made resistance-heated floated zone furnace. The temperature-dependent resistance and Hall voltage confirm that the transport is metallic and the overall carriersareholes. The angle and temperature dependence of the quantum Shubnikov–de Haas oscillation period amplitude suggests that the transport comes from the carriers of surface states. The Berry phase, determined from Landau level diagram, also reveals that the transport carriers are Dirac fermions. In contrast with many previous publications, the transport parameters relating to the surface carriers derived from the relationship of the Lifshitz–Kosevich (LK) theory are consistent with angle resolved photoemission spectroscopy results.