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Er-doped ZnO (Zn (1-x) Er (x) O) films with (002) preferential orientated wurtzite structure were fabricated on a c-plane sapphire substrate by pulsed laser deposition (PLD). The effects of Er composition, oxygen pressure during growth, and post-growth annealing on the films' structural, electrical, and optical properties were studied by employing a comprehensive spectroscopic approach. Er-doped ZnO films with a resistivity of 4 × 10−4 Ωcm, electron conductivity n+∼1021 cm−3, and high optical transmittance (>90%) were disclosed to be appropriate candidates for transparent conducting electrode applications. A shallow donor is reported to be associated with the Er Zn defect, which is optically inactive. Er-doped ZnO samples grown with high Er composition and oxygen pressure don't show n+ conductivity because of the formation of an O-rich Er Zn -related compensating defect. Annealing at 750 °C converts the Er Zn shallow donor to another defect configuration, which is optically active for intra-4f-shell transition emissions, but no longer a shallow donor. The growth condition for maximizing the intra-4f-shell transition emission was also obtained. [ABSTRACT FROM AUTHOR]

SnTe is receiving a lot of attention as a topological crystalline insulator. Herein, SnTe films are grown directly on GaAs (100) substrates by molecular beam epitaxy. The surface morphology and electronic properties are measured by atomic force microscopy and Hall effect measurement, respectively. Considering previous X‐ray diffraction results, the samples grown with high beam‐intensity ratios show hexagonal Te segregation in the films, which deteriorates the surface morphology and decreases the conductivity. By suppressing the supply of Te, better surface morphology and electrical properties are obtained. [ABSTRACT FROM AUTHOR]

• This work highlights the differences and similarities of charge transport mechanisms of SiOC monolithic and thin-film samples. • The effect of varying the structure going from bulk to thin-film sample to improve the electrical transport mechanism in C/SiOC is established in this work. • It is found that the substrate induces compressive strain on the film in the biaxial direction which boosts the charge carrier mobility of the material. • The decrease in activation energy, Ea ca. 0.07 eV, is correlated to the increased size of the sp2 carbon domains with an average of ca. 40 nm which supports the positive effect of the microstructure of the film. • Hall measurement revealed p-type carriers as the main charge carrier of the system. • The charge carrier concentration of both monolith and thin-film samples is found to be comparable while a significant increase in mobility, by 2 orders of magnitude, is realized for the SiOC thin film. • The conductivity of the C/SiOC thin film, ca. 16 S cm-1, is also 2 magnitudes higher as compared to monolithic samples and is supposed to rely on the improved charge carrier mobility as well as on the decreased percolation threshold due to the phase-separated morphology of the thin film. • The present study indicates that the charge carrier transport in SiOC-based systems can be modulated not only by adjusting the chemical composition (i.e., carbon content) of SiOC but also by tailoring its morphology and residual stress. This work correlates the charge carrier transport mechanism of silicon oxycarbide-based thin films with their morphology and thermal stress. Segregation of highly-graphitized carbon-rich, oxygen-depleted C/SiC areas homogeneously dispersed within an oxygen-rich C/SiOC matrix was seen on the 500 nm-SiOC thin films. Compressive biaxial stress induced by the mismatch with the Si-substrate thermal expansion coefficient was calculated at 109 MPa. Through Hall measurements, p-type carriers were shown dominating the SiOC film similar to monolithic samples. Thin films and monoliths have comparable carrier concentrations while the carrier mobility in SiOC thin films was 2 magnitudes higher than that of monolithic samples and is considered a consequence of the compressive thermal stress acting on the film. Improved conductivity of 16 S cm -1 is measured for the SiOC thin film sample which is assumed considering the enhanced carrier mobility alongside the reduced percolation threshold ascribed to the phase-separated morphology of the thin film. [ABSTRACT FROM AUTHOR]

A comprehensive investigation on the low-field 2-DEG mobility in InxAl1-xN/AlN/GaN heterostructure has been made through Hall experimental and numerical calculation based on an ensemble Monte Carlo (MC) approach. Hall measurement on a lattice-matched (LM) In0.18Al0.82N/AlN/GaN heterostructure grown by metal-organic chemical vapor deposition (MOCVD) has been carried out as a function of temperature ranging from 77 to 405 K. A more rigorous model is presented taking both inter- and intra-subband scattering into account. The scattering rates are derived from the results of the electron density, the quantized energy levels, and the corresponding wave functions based on the self-consistent solutions of Poisson’s and Schrödinger’s equation given in our previous work. We confirm that the interface scattering process dominates the mobility within the low temperature (77–130 K), as increasing of the temperature, the highly inelastic scattering caused by partial occupation of the higher subband is responsible for the rapid degradation of the 2-DEG mobility. The role of surface morphology and indium fraction of the heterostructure on the dependence of the 2-DEG mobility have been clarified qualitatively in detail. The calculated results are widely compared with the published literature and our experimental finding. A reasonable agreement is achieved. [ABSTRACT FROM AUTHOR]

We make a new type of bipolar Schottky diodes using the p-type La 2/3 Sr 1/3 VO 3 (LSVO)/n-TiO 2 heterostructure. The p-type LSVO metal thin films are grown on various substrates using radio frequency magnetron co-sputtering deposition. We find that the LSVO film grown on anatase TiO 2 layer produce the lowest resistivity of 0.28 mΩ cm. We discover that the resistivity decreases with decreasing LSVO film thickness for LSVO/TiO 2 /Si structures. Hall measurements are performed and the dielectric functions of LSVO films are measured. The effective mass of LSVO/TiO 2 /Si is determined to be 2.54 ± 0.05 m 0. The current-voltage curves of the Schottky diodes of p-LSVO/n-TiO 2 is measured and is explained using band alignment diagram. We identify a new type of Schottky diode, where both electrons in n-TiO 2 and holes in p-LSVO can flow under bias. Conventional Schottky diodes are unipolar devices. We make a new type of bipolar Schottky diodes using p-type La 2/3 Sr 1/3 VO 3 /n-type TiO 2 heterostructure. The diode behavior of current-voltage curve is explained using band level alignments measured using ultra-violet photoemission spectroscopy and spectroscopic ellipsometry. The large effective mass of the hole carriers of p-La 2/3 Sr 1/3 VO 3 metallic films reveals a strong correlation between the hole carriers. Image 1 • A new type of bipolar Schottky diodes using the p-La 2/3 Sr 1/3 VO 3 /n-TiO 2 heterostructure. • Band energy alignments of p- La 2/3 Sr 1/3 VO 3 /n-TiO 2 heterostructure are determined to explain current-voltage curves. • La 2/3 Sr 1/3 VO 3 films grown on anatase TiO 2 /Si had the lowest resistivity (0.28 mΩ cm). • The effective mass of the La 2/3 Sr 1/3 VO 3 films was determined as 2.54 m 0. [ABSTRACT FROM AUTHOR]

Zinc selenide (ZnSe) thin films with various thicknesses were grown on ultrasonically clean glass substrates using vacuum evaporation of 99.99% pure ZnSe powder. Thickness dependence of the structural, optical and electrical properties was thoroughly investigated. X-ray diffraction (XRD) analyses revealed that (110) ZnSe plane is the dominant crystal plane for all the fabricated films. Both dislocation density and micro-strain go down with the increase in film thickness, indicating lower lattice defects and improvement in crystallinity at higher film thickness. Transmittance spectra show that all the films have almost linear upward tendency of transmittance in near-infrared region and small fluctuations in visible region for higher-thickness films. With the increase in film thickness, the optical bandgap increases and also an increasing tendency of dielectric constant was observed. Studies of electrical properties showed a sharp increase in carrier mobility and concentration with film thickness. As the film thickness increases from 30 to 90 nm, the carrier mobility goes up from 255 to 1250 cm2/VS and the carrier concentration increases from 2.14 × 1018 to 9.37 × 1018 cm−3. The electrical transport properties of the deposited thin films were explained in terms of scattering of the charge carrier. [ABSTRACT FROM AUTHOR]

Partially nitrided LiCoO2 thin films with stoichiometric contents of Li and Co were fabricated on sapphire substrates using an ethanol solution. The precursor films were formed by spin-coating. By thermal treatment of' the precursor films at 350, 450, 550 and 650°C for 30 min in air, four kinds of LiCoO2 thin films were obtained. That annealing of the precursor film at 650°C resulted in the nucleation of Co3O4 from the layered LiCoO2, which has been confirmed by the Raman spectrum. Three X-ray photoelectron spectroscopy peaks observed at 527.9 eV, 402.1 eV, and 396.2 eV were newly assigned to the O-Co4+, N-Co4+, and N-Co2+ bonds, respectively, using a peak-analysis technique. The resistivity of the layered LiCoO2 thin film fabricated at 650°C was measured to be 1.2 Ω cm. [ABSTRACT FROM AUTHOR]

Narrow band-gap semiconductors, namely ternary InAsSb alloys, find substantial technological importance for mid-infrared application as photodetectors in medical diagnostics or environmental monitoring. Thus, it is crucial to develop electrical contacts for these materials because they are the fundamental blocks of all semiconductor devices. This study demonstrates that electroplated gold contacts can be considered as a simple and reliable metallization technology for the electrical-response examination of a test structure. Unalloyed electroplated Au contacts to InAsSb exhibit specific contact resistivity even lower than vacuum-deposited standard Ti–Au. Moreover, temperature-dependent transport properties, such as Hall carrier concentration and mobility, show similar trends, with a minor shift in the transition temperature. It can be associated with a difference in metallization technology, mainly the presence of a Ti interlayer in vacuum-deposited contacts. Such a transition may give insight into not only the gentle balance changes between conductivity channels but also an impression of changing the dominance of carrier type from p- to n-type. The magnetotransport experiments assisted with mobility spectrum analysis clearly show that such an interpretation is incorrect. InAsSb layers are strongly p-type dominant, with a clear contribution from valence band carriers observed at the whole analyzed temperature range. Furthermore, the presence of thermally activated band electrons is detected at temperatures higher than 220 K.

γ-MnS thin films were prepared on glass substrate by spray pyrolysis method at 280 °C. The optical constants and thickness of the films were extracted using the pattern search optimization technique in combination with a seed preprocessing procedure (spPS). Refractive index dispersion of the films was analyzed by using the concept of the single oscillator model. The values of the oscillator energy, E0, and the dispersion energy, Ed, were determined as 8.83 eV and 5.65 eV, respectively. The analysis of the optical properties of the γ-MnS film showed a direct transition with energy band gap of 2.74 eV. Utilizing Hall Effect measurement, we have determined values of the resistivity p which equals to 1150 Ocm. The positive value of hall coefficient showed a p-type in nature of the obtained thin film. The maximum of photocurrent density estimated by Yablonovitch limit is equal to 46 mA/cm2. [ABSTRACT FROM AUTHOR]

Abstract Tin sulfide (SnS) thin film was deposited on glass substrates using simple nebulizer spray pyrolysis method. The influence of vacuum annealing on structural, optical, morphological, electrical and photovoltaic properties of the films were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy, atomic force microscopy, energy dispersive analysis of X- ray, UV-Visible spectrophotometry, photoluminescence spectrofluorometry and Hall measurements. Structural parameters such as lattice structure, crystallite size, micro strain and dislocation density were estimated using XRD analysis. There was a notable enhancement in morphology and surface roughness of the films and they were found to vary with respect to the annealing temperature. Optical studies done on the films revealed a decrease in energy gap for the increase of annealing temperatures. From the Hall effect study, it was found that SnS thin films have p-type conductivity. The lowest resistivity and higher carrier concentration were found to be 0.074 Ω cm and 1.07 × 1019 (cm−3) respectively. A heterojunction solar cell, CdS/SnS was fabricated and its solar conversion efficiency obtained was about 0.73% for tin sulfide films annealed at 400 °C. Highlights • Tin sulfide (SnS) films grown by using simple nebulizer spray pyrolysis technique. • Improvement in the structural and morphological properties of the film was observed after annealing. • Optimized SnS film is used for n-CdS/p-SnS structured solar cell. • The conversion efficiency of about η = 0.73% was obtained using SnS heterojunction. [ABSTRACT FROM AUTHOR]

Herein we report a well-organized analysis on various key-properties of SnS thin films for solar cell fabricated by nebulizer spray pyrolysis technique. X-ray diffraction study reveals the polycrystalline nature of deposited films with orthorhombic crystal structure. The crystallite size was calculated and observed to be in the range of 8–28 nm with increasing molarity of precursor solution. The stoichiometry composition of SnS was confirmed by EDX study. SEM/AFM studies divulge the well-covered deposited surface with spherical grains and the size of grains is increasing with concentration and so the roughness. A remarkable decrease in band gap from 2.6 eV to 1.6 eV was noticed by raising the molar concentration from 0.025 M up to 0.075 M. A single strong emission peak at about 825 nm is observed in PL spectra with enhanced intensity which may be attributed to near band edge emission. From the Hall effect measurement, it was found that the SnS thin film exhibits p-type conductivity. The calculated values of resistivity and carrier concentration are 0.729 Ω cm and 3.67 × 10 18 /cm 3 respectively. Furthermore, to study the photovoltaic properties of SnS thin films a heterojunction solar cell, FTO/n-CdS/p-SnS was produced and the conversion efficiency was recorded about 0.01%. [ABSTRACT FROM AUTHOR]

The quality of graphene strongly affects the performance of graphene-based biosensors which are highly demanded for the sensitive and selective detection of biomolecules, such as DNA. This work reported a novel transfer process for preparing a residue-free graphene film using a thin gold supporting layer. A Hall effect device made of this gold-transferred graphene was demonstrated to significantly enhance the sensitivity (≈ 5 times) for hybridization detection, with a linear detection range of 1 pM to 100 nM for DNA target. Our findings provide an efficient method to boost the sensitivity of graphene-based biosensors for DNA recognition. [ABSTRACT FROM AUTHOR]

Transparent conductive Ga-doped ZnO (GZO) thin films were grown on glass substrates by pulsed laser deposition using 2 at% Ga 2 O 3 doped ZnO target. A Substrate temperature of 400 °C and oxygen pressure of 7 × 10 −3 Torr was kept constant during the deposition. The effects of laser pulse repetition rate from 3 to 15 Hz on crystallographic, surface morphological, optical and electrical properties of the GZO films were investigated. All the samples show the hexagonal wurtzite phase with a dominant c-axis orientation and the optimal crystallization of the GZO film occurs at 10 Hz; which is slightly better that of the film deposited at 5 Hz. AFM and FE-SEM analysis revealed that the film growth is profoundly influenced by the pulse repetition rate and the film thickness increases with an increase in the pulse repetition rate due to enhancement in deposition rate and the island density. Hall-effect measurements confirmed that all samples are heavily doped degenerate semiconductors with n-type electrical conductivity. The electrical transport properties of the film are found to be largely dependent on the crystallinity; while their optical transmittance is majorly dominated by the film thickness and roughness. The GZO film deposited at 5 Hz shows the highest figure of merit (76.11 × 10 −3 /Ω) as a result of its optimum sheet resistance (3.63 Ω /□ ) and optical transmittance (∼88%). [ABSTRACT FROM AUTHOR]

In this paper, we experimentally studied the effect of AlN spacer layer on optical and electrical properties of AlGaN/GaN high electric mobility transistors (HEMTs) grown by metal organic chemical vapor deposition method. For AlGaN layer in HEMT structure, the Al composition of the sample was determined using x-ray diffraction and photoluminescence. Electrolyte electro-reflectance (EER) measurement not only confirmed the aluminum composition of AlGaN layer, but also determined the electric field strength on the AlGaN layer through the Franz-Keldysh oscillation phenomenon. This result indicated that the electric field on the AlGaN layer could be improved from 430 to 621 kV/cm when AlN spacer layer was inserted in HEMT structure, which increased the concentration of two dimensional electron gas (2DEG) and improve the mobility. The temperature dependent Hall results show that both the mobility and the carrier concentration of 2DEG would decrease abruptly causing HEMT loss of function due to phonon scattering and carrier thermal escape when temperature increases above a specific value. Meanwhile, our study also demonstrates using AlN spacer layer could be beneficial to allow the mobility and carrier density of 2DEG sustaining at high temperature region. [ABSTRACT FROM AUTHOR]

Hall effect is a very popular technique and is widely used to quantify important electrical parameters such as carrier concentration, resistivity, mobility and Hall coeffi cient of different types of samples. In this paper, electrical characteristics of three ceramic samples will be analyzed using a Hall effect measurement system (Ecopia, HMS-3000), which is based on the van der Pauw method. Measured results for mobility and electrical resistivity at three temperatures (25°C, 50°C and 80°C) will be presented. Current-voltage and current-resistance dependence between terminals of four point contact of different samples will be also demonstrated.

Highlights: [•] Textured ZnO ultra thin films are grown using MOCVD technique. [•] Growth mode dependent microstructures are fabricated. [•] The microstructure formation is understood on the basis of van der Drift model. [•] Hall effect measurement provides reliable results. [•] Correlation between the microstructures and the gas sensing behavior is explained. [ABSTRACT FROM AUTHOR]

Indium zinc tin oxide (IZTO) thin films were deposited on glass substrate by radio frequency magnetron sputtering at various substrate temperatures. The indium content of the IZTO targets was reduced from 60at.% to 30at.% and replaced with equal amounts of zinc and tin (20, 25, 30, and 35at.%). The crystallinity of the as-deposited films improved with increasing substrate temperature. For all IZTO films, the onset of crystallization began at above 100°C. The IZTO films deposited at higher substrate temperature showed better optical transmittance and lower electrical resistivity than those deposited at lower temperatures. The minimum electrical resistivity of approximately 8.0×10−4 Ω·cm was observed in the IZTO films prepared deposited at 400°C from targets containing 20at.% Zn and 20at.% Sn. The optical transmittance was above 80% for all IZTO films. On the other hand, higher co-doping resulted in amorphous films, which slightly impaired the electrical properties. The deterioration in the electrical properties of IZTO films, however, was compensated for by the higher optical transparency. Therefore, reduced-indium IZTO films are promising alternatives for some transparent conducting oxide applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A series of N-doped carbon dots were synthesized by varying the citric acid to urea ratio in the precursors. • The effects of nitrogen doping on chemical, optical and electronic properties of carbon dots were systematically characterized. • The insights acquired are instructive for designing carbon dots, and optical and electronic devices based on them. Photoluminescent carbon dots have received significant research interest in recent years owing to their extraordinary optical properties, biocompatibility, and versatile functionalities. Nitrogen-doping is a widely used strategy for enhancing the photo-electronic functionalities of carbon dots. However, there is a lack of systematic study on the composition and concentration-dependency emission behaviour of N-doped carbon dots in the literature. In this study, multicolour carbon dots (CDs) having different degree of nitrogen doping were synthesized by varying the molar ratio of citric acid to urea in the precursor via hydrothermal treatment. The effects of nitrogen doping on chemical, optical, and electronic properties of CDs were characterized using various techniques including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR); fluorescence and absorption spectroscopy; fluorescence lifetime and Hall effect measurements. Three main emissive centres were recognized in concentration-dependent fluorescence study of N-CDs which can be ascribed to molecular type of fluorescence, core emission, and mid-gap nitrogen states on the edge/surface of CDs. A plausible mechanism in relation to the obtained results is proposed. This work provides insights on the opto-electro-tunability of CDs via N-doping. [ABSTRACT FROM AUTHOR]

Highlights: [•] Important report on simplified spray deposited In-doped ZnO films. [•] PL, electrical and structural results are corroborated with each other. [•] Enhancement of electrical parameters by means of indium-doping. [•] Smooth nanostructures are grown along c-axis. [•] The linear dependence of physical properties on the substrate temperature of as-grown films is confirmed. [ABSTRACT FROM AUTHOR]

Abstract: The effect of annealing temperature on photoelectric properties of metal–semiconductor–metal (MSM) black silicon photodetector has been studied. The black silicon was fabricated by alkaline etching and metal assisted etching. The nanopores and micro-columns formed by the etching process enhance spectral absorptance significantly at wavelength from 250nm to 1100nm. The MSM black silicon photodetectors were annealed at different temperatures in N2 ambient with a rapid thermal annealing (RTA) process. The fast ramp-up and cool-down rate of RTA is a key factor that eliminates the tensile stress and point defects in Si nanoparticle made from metal assisted wet etching, leading to significant increase of mobility, conductivity and carrier concentration. In addition, the photocurrent and spectral responsivities of detectors increase with annealing temperature. At the wavelength of 600nm, the responsivity (76.8A/W) at 673K is almost three orders of magnitude greater than that of the unannealed sample. [Copyright &y& Elsevier]

Abstract: Indium zinc tin oxide (IZTO) thin films with two different chemical compositions, i.e. IZTO15 and IZTO25, where In content was fixed at 60 at.% and Sn content was 15 and 25 at.%, respectively, were deposited onto alkaline-free glass substrate at temperature from 37°C to 600°C. The deposition process was carried out in argon using an RF magnetron sputter. After deposition, the films were annealed in argon atmosphere at 450°C for 30 min. The effect of substrate temperature and annealing treatment was investigated, and the minimum resistivity value of 3.44×10−4Ω.cm was obtained from the film deposited at 400°C using IZTO25 target followed by rapid thermal annealing at 450°C for 30 min. The average optical transmittance was kept fairly high over 80%. It was proven that both substrate temperature and thermal annealing were important parameters in lowering the electrical resistivity without deteriorating optical properties. [Copyright &y& Elsevier]

Abstract: The gallium doped zinc oxide has been one of the candidates for the transparent conducting oxide thin film electrode. It is not suitable to use a conventional light interference method to measure the thickness of the gallium doped zinc oxide thin film because the refractive index and extinction coefficient of the thin film is unknown during the optimization of the deposition conditions. In this paper, we report on the details of the film thickness program which uses the measured optical and electric properties and relationship between the plasma frequency and the optical constant of the film. The obtained film thickness of the prepared gallium doped zinc oxide thin film using the program was comparable with thicknesses measured by a cross-sectional analysis of the atomic force microscopy and the surface profiler. Moreover, the optical constant of refractive index and extinction coefficient of the film could also be estimated. [ABSTRACT FROM AUTHOR]

The course "Materials in Electrical Engineering" is a core course in the Mechatronics curriculum at the Faculty of Technical Sciences, University of Novi Sad, Serbia. In the past, this course was comprehensive and mainly theory-based. Teaching methods used in this course had not been changed for many years, and were mainly based on a traditional approach. They were therefore often outdated, and boring for students. In addition, the lack of modern materials characterization equipment was a significant weakness of the course in its early stages. This paper presents the main aspects of the modified course, which features a greater inclusion of modern equipment in its teaching methodology; in particular it produces the Hall effect measurement system as an indispensable characterization technique in education, research and in the semiconductor industry. This paper also describes how students can be taught to use the Hall effect measurement system to determine the structural and electrical characteristics of different materials. Finally, students' feedback and observations on the modified course and the applied teaching methodology are discussed. [ABSTRACT FROM AUTHOR]

Abstract: In this report, we present a study on lattice and electronic structures of B doped layers formed using B implantation into diamond. Boron layers were produced using the multiple-energy B ion implantation (total dose: 2.1×1015 to 1.7×1017 cm−2) into type IIa diamond at ~400 °C. Optical absorption and Hall effects were measured in the range of 80−1000 K for investigating the change of the lattice and electronic structures with the B concentration in diamond. The p-type carrier conduction was observed at 80−1000 K in all the samples. While a lightly B doped sample displays typical semiconductive, temperature-dependent valence-band conduction, heavily B doped samples have the very weak or almost zero temperature dependence of the carrier concentrations, resistivity and Hall mobility in this temperature region, suggesting characteristics of a p-type degenerate semiconductor. In such heavily doped samples, broad optical absorption bands, most likely corresponding to Drude absorption originating from free holes, were observed. The minimum resistivity and the sheet resistance at room temperature among the samples were 1.4 mΩcm and 56 Ω/□, respectively. These results indicate that very low-resistive p-type degenerate semiconducting layers were produced, preserving diamond lattice (preventing graphitization), despite high-dose ion irradiation. [Copyright &y& Elsevier]

Abstract: Changes in electrical as well as surface composition such as chemical and electronic properties of Mg-doped p-type GaN by phosphorus implanting are systematically investigated using Hall effect and X-ray photoelectron spectroscopy (XPS) measurements. It is shown that p-type conductivity of Mg-doped GaN can be improved by implanting P atoms after a proper post-implantation annealing treatment, probably due to the reduction of self-compensation by P atoms substitution on N vacancy sites. XPS analysis is further found that the decrease of surface oxides and the shift of the surface Fermi level toward the valence band edge through P atoms introduced. These experimental results indicate that the P implantation is an effective method to improve p-type conductivity of Mg-doped GaN and reducing the surface barrier height, which can lead to a lower metal contact resistivity to p-type GaN. [Copyright &y& Elsevier]

Abstract: The dependence of electrical and structural properties on film thickness was studied on polycrystalline undoped zinc oxide (ZnO) thin films on glass substrates at 200 ∘C prepared by plasma-assisted electron-beam deposition. The film thickness was varied from 23 to 316 nm. Hall effect measurements for undoped ZnO films showed that while the Hall mobility increased with increasing film thickness up to almost 130 nm, it remains almost constant on further increasing the film thickness (>130 nm). The carrier concentration changes a little. As a result, the dependence of the resistivity on film thickness was determined by that of Hall mobility. It was clarified by out-of-plane and in-plane X-ray diffraction (XRD) that while the orientation of undoped ZnO with a thickness below 130 nm is random, ZnO films with a larger thickness (>130 nm) change to -axis orientation. In-plane XRD line broadening analysis, using the Williamson–Hall method, reveals that both the crystallite size and remaining microstrain increase with increasing film thickness. The same tendency of the averaged surface roughness (Ra), from atom force microscopy (AFM) measurement, as that of the structural and physical properties described above was observed. [Copyright &y& Elsevier]

Very high quality p-type AlxGa1−xN/GaN superlattice has been achieved through optimization of Mg flow and period of superlattice. Theoretical model was used to optimize the structure of superlattice by choosing suitable Al compositions and superlattice periods. The experiments show that for x=0.26, the resistivity is as low as 0.19 Ω cm and hole concentration is as high as 4.2×1018 cm−3, the highest values ever reported for p-type AlGaN/GaN superlattices. Hall effect measurement and admittance spectroscopy on the samples confirm the high quality of the superlattices. The activation energy calculated for p-type GaN and p-type A0.1Ga0.9N/GaN superlattice is estimated to be ∼125 and 3 meV respectively. [Copyright &y& Elsevier]

Ternary Ta2NiSe5 is a novel electronic material having the property of an excitonic insulator at room temperature. The electrical properties of Ta2NiSe5 have not been elucidated in detail. We discuss the electronic properties in Ta2NiSe5 films and the formation of heterojunctions. Hall effect measurements showed p-type conductivity. The activation energies estimated from the temperature dependence of the carrier concentration were seen to be 0.17 eV and 0.12 eV, at approximately 300 and 400 K, respectively. It was observed that carrier generation behavior changes at the critical temperature of the excitonic insulator state (328 K). The temperature dependence of the Hall mobility below the critical temperature nearly follows the bell-shaped curves for conventional semiconductor materials. A MoS2/Ta2NiSe5 van der Waals heterojunction was fabricated using the transfer method. Rectification characteristics, which depend on the gate bias voltage, were obtained. The barrier height at the MoS2/Ta2NiSe5 heterointerface and the on/off ratio could be modulated by applying a gate bias voltage, suggesting that the carrier transport was exhibited in band-to-band flow. Our demonstration suggests that the knowledge of Ta2NiSe5 increased as an electronic material, and diode performance was successfully achieved for the electronic device applications. [ABSTRACT FROM AUTHOR]

Narrow band-gap semiconductors, namely ternary InAsSb alloys, find substantial technological importance for mid-infrared application as photodetectors in medical diagnostics or environmental monitoring. Thus, it is crucial to develop electrical contacts for these materials because they are the fundamental blocks of all semiconductor devices. This study demonstrates that electroplated gold contacts can be considered as a simple and reliable metallization technology for the electrical-response examination of a test structure. Unalloyed electroplated Au contacts to InAsSb exhibit specific contact resistivity even lower than vacuum-deposited standard Ti–Au. Moreover, temperature-dependent transport properties, such as Hall carrier concentration and mobility, show similar trends, with a minor shift in the transition temperature. It can be associated with a difference in metallization technology, mainly the presence of a Ti interlayer in vacuum-deposited contacts. Such a transition may give insight into not only the gentle balance changes between conductivity channels but also an impression of changing the dominance of carrier type from p- to n-type. The magnetotransport experiments assisted with mobility spectrum analysis clearly show that such an interpretation is incorrect. InAsSb layers are strongly p-type dominant, with a clear contribution from valence band carriers observed at the whole analyzed temperature range. Furthermore, the presence of thermally activated band electrons is detected at temperatures higher than 220 K. [ABSTRACT FROM AUTHOR]

Al doped ZnO (AZO) is a promising transparent conducting oxide to replace the expensive Sn doped In 2 O 3 (ITO). Understanding the formation and evolution of defects in AZO is essential for its further improvement. Here, we synthesize transparent conducting AZO thin films by reactive DC magnetron sputtering. The effects of oxygen flow ratio as well as the rapid thermal annealing (RTA) in different conditions on their structural and optoelectrical properties were investigated by a variety of analytical techniques. We find that AZO thin films grown in O-rich conditions exhibit inferior optoelectrical performance as compared with those grown in Zn-rich conditions, possibly due to the formation of excessive native acceptor defects and/or secondary phases (e.g. Al 2 O 3 ). Temperature-dependent Hall measurements indicate that mobilities of these highly degenerate AZO films with N > 10 20  cm -3 are primarily limited by ionized and neutral impurities, while films with relatively low N ∼ 10 19  cm -3 exhibit a temperature-activated mobility owing to the grain-barrier scattering. As N increases, the optical band gap of AZO thin film increases as a result of Burstein-Moss shift and band gap narrowing. RTA treatments under appropriate conditions (i.e. at 500 °C for 60 s in Ar) can further improve the electrical properties of AZO thin film, with low resistivity of ∼6.2 × 10 -4 Ω cm achieved, while RTA at high temperature with longer time can lead to the formation of substantial sub-gap defect states and thus lowers the electron mobility. X-ray photoelectron spectroscopy provides further evidence on the variation of Al (Zn) content at the surface of AZO thin films with different processing conditions., (© 2021 IOP Publishing Ltd.)

• Zn- and O-polar ZnO films grown by pulsed laser deposition were characterized. • Their electrical and optical properties are dependent on the polarity. • The differences in the properties are explained by the presence of different defects. O-polar and Zn-polar ZnO films were grown on c-sapphire by pulsed laser deposition. Positron annihilation spectroscopy study reveals that the V Zn -related defects in the ZnO films with different polarities are different in structure and their thermal evolution is different. Hall effect measurement and luminescence spectroscopy reveal that the electrical and optical properties and their corresponding thermal evolution are strongly dependent on the polarity of the film. The luminescence spectra of the as-grown Zn-polar ZnO film is signified by a negligible green defect emission (at ~ 2.4 eV) and strong near band edge emission as compared with the O-polar film. The as-grown Zn-polar film exhibited a lower electron concentration (2 × 1018 cm−3) than that of the O-polar film (6 × 1018 cm−3); this difference is attributed to their different H concentrations. For the O-polar film, the electron concentration decreased with annealing temperature T anneal , reaching a minimum at 700°C and then increased to 4 × 1018 cm−3 at T anneal = 900 °C. In comparison, the electron concentration of the Zn-polar ZnO film monotonically decreased with T anneal attaining a value of ~1 × 1017 cm−3 at T anneal = 900 °C, 40 times smaller than that of the O-polar film. The cause for the differences in the optical and electrical properties for the O-polar and Zn-polar films is explained by the presence of different defects in these films. [ABSTRACT FROM AUTHOR]

• CdS thin films were deposited onto glass substrates by RF sputtering. • Crystallite size increases with increasing substrate temperature and thus reducing the grain boundaries in the films. • Resistivity of the films decreases with increasing substrate temperature. We report the effect of substrate temperature (25–300 °C) on the structural, optical and electrical properties of Cadmium Sulphide (CdS) thin films deposited onto glass substrate by Radio Frequency (RF) magnetron sputtering. The structural, morphological, optical and electrical properties of the films were characterized by X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), UV–VIS-NIR spectroscopy and Hall Effect measurement respectively. The XRD studies showed that the films were polycrystalline with hexagonal wurtzite structure preferentially oriented along the (0 0 2) plane parallel to the substrate surface. The XRD data analysis further revealed the crystallite size of the nanocrystalline films i.e. 22–24 nm exhibiting the fact that crystallite size increased with increasing the substrate temperature. The FE-SEM images along with energy dispersive spectroscopy (EDS) studies confirmed the homogeneous, compact and pin-hole free surface morphology. The UV–VIS-NIR studies unveiled the optical transmittance in the range of 75–90% after 540 nm of the wavelength of light. The optical band gaps were found to be decreasing from 2.34 eV to 2.26 eV with increasing the substrate temperature. The films were characterized as n-type as evidenced by the Hall Effect measurement. The carrier mobility was found to be increasing gradually from 5.53 to 12.57 cm2/V·s by increasing the substrate temperature from room temperature to 300 °C due to the improvement of crystalline quality and grain size of the films. The results showed good optical and electrical properties of the films deposited at 300 °C which are suitable to use as window layer in thin film based solar cells. [ABSTRACT FROM AUTHOR]

The capability of graphene-based biosensors used to detect biomolecules, such as DNA and cancer marker, is enormously affected by the quality of graphene. In this work, high quality and cleanness graphene were obtained by CVD based on acetic acid (AA) and ammonium persulfate (AP) pretreated copper foil substrate. Hall effect devices were made by three kinds of graphene which were fabricated by CVD using no-treated copper foil, AA pre-treated copper foil and AP pre-treated copper foil. Hall effect devices made of AA pre-treated copper foil CVD graphene and AP pre-treated copper foil CVD graphene can both enhance the sensitivity of graphene-based biosensors for DNA recognition, but the AA pre-treated copper foil CVD graphene improves more (≈4 times). This may be related to the secondary oxidation of AP pre-treated copper foil in the air due to the strong corrosion of ammonium persulfate, which leads to the quality decrease of graphene comparing to acetic acid. Our research provides an efficient method to improve the sensitivity of graphene-based biosensors for DNA recognition and investigates an effect of copper foil oxidation on the growth graphene. [ABSTRACT FROM AUTHOR]