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A novel and facile hydrothermal route was designed to produce h-BN-C quantum dots (h-BN-C QDTs) using h-BN powder as a precursor and Potassium Sodium Tartare as an intercalant. The resulting yellow solution possessed mono or few-layers of quantum dots with an average size of ~2.5 nm. Due to the incorporation of functional groups (carbon, oxygen) on the surface of h-BN, an enhancement of photo luminescent magnitude and a blue shift were observed in photoluminescence spectra from h-BN-C QDTs solution. Further, h-BN-C QDTs exhibits a bright blue fluorescence under the irradiation by a 365 nm UV light. Next, h-BN QDTs was utilized as the dielectric active layer by using simple drop casting method between the electrodes and fabricated the nonvolatile resistive switching devices. The fabricated devices exhibited the nonvolatile bipolar resistive switching characteristics with 103 ON/OFF ratio and turned ON and OFF threshold voltages of −1.9 V and +1.4 V, respectively. Further, the switching mechanisms of h-BN-C QDTs were found to be space charged trapping. It provides a route toward tailoring the optical and electrical properties of the h-BN materials and can be utilized in the future potential applications.

The effects of rapid thermal annealing temperature on structural, morphological, and optical properties of copper phthalocyanine (CuPc) films on n-Si are investigated. The deposited CuPc films on n-Si substrate form nanoparticles and are slightly elongated with an increase in surface roughness with increase in annealing temperature due to the aggregation of the native grains. The electrical and current transport properties of a fabricated Au/CuPc/n-Si metal-polymer-semiconductor (MPS)-type Schottky barrier diodes (SBDs) are explored at various annealing temperatures (range 100–300 °C) by current–voltage (I–V) and capacitance–voltage (C–V) measurements. Results reveal that the estimated barrier height decreases with increasing annealing temperature and could be ascribed to the diffusion of Au atoms into CuPc films transferring negative charges to the molecule inducing an n-type doping of the organic film. An analysis of the forward log (I)–log (V) plot of Au/CuPc/n-Si (MPS)-type SBDs indicated the carrier transport domination by ohmic conduction in the lower bias and by the space-charge-limited current (SCLC) transport mechanism at higher bias regions irrespective of annealing temperatures that might be related to additional traps initiating from the CuPc. Poole–Frenkel emission governs the current transport in the reverse bias regardless of annealing temperature.

There is a recent interest in semiconducting superlattice films because their low dimensionality can increase the thermal power and phonon scattering at the interface in superlattice films. However, experimental studies in all cross-plane thermoelectric (TE) properties, including thermal conductivity, Seebeck coefficient, and electrical conductivity, have not been performed from these semiconducting superlattice films because of substantial difficulties in the direct measurement of the Seebeck coefficient and electrical conductivity. Unlike the conventional measurement method, we present a technique using a structure of sandwiched superlattice films between two embedded heaters as the heating source, and electrodes with two Cu plates, which directly enables the investigation of the Seebeck coefficient and electrical conductivity across the Al2O3/ZnO superlattice films, prepared by the atomic layer deposition method. Used in combination with the promising cross-plane four-point probe 3-ω method, our measur...

The temperature-dependent current-voltage (I-V) characteristics of permalloy (Ni0.8Fe0.2) Schottky contacts to n-type GaN have been investigated. Magnetization measurements revealed the ferromagnetic behavior of Ni0.8Fe0.2 film on n-type GaN. The Schottky barrier parameters, such as the barrier height and ideality factor, determined by thermionic emission depended on the measurement temperature, suggesting the presence of lateral inhomogeneity in the Schottky barrier. The experimental data modified by the thermionic emission model along with a Gaussian distribution of the barrier heights indicated the presence of a double Gaussian barrier distribution in the Ni0.8Fe0.2/n-type GaN Schottky contact. The mean barrier heights and standard deviations for each Gaussian distribution were 0.84 & 1.32 eV and 0.10 & 0.17 eV over temperature range of 125–200 K and 225–400 K, respectively. The noise spectral density of the current fluctuations measured as a function of frequency (f) at room temperature followed a 1/fγ dependence with a γ value close to unity, irrespective of the applied forward bias. The 1/f-type noise was attributed to the barrier inhomogeneity existing at the Ni0.8Fe0.2/n-type GaN Schottky interface as revealed from the temperature-dependent I–V characteristics.

Ge p-i-n photodetectors with and without graphene on active area fabricated and investigated the graphene effects on opto-electrical properties of photodetectors. The photodetectors were characterized with respect to their dark, photocurrents and responsivities in the wavelength range between 1530-1630 nm. For a 250 um-diameter device at room temperature, it was found that dark current of p-i-n photodetector with graphene were reduced significantly compared with photodetector without graphene. This improvement is attributed to the passivation of the graphene layers that leads to the efficient light detection. Therefore, it is noted that the uniform coverage of graphene onto the Ge surface plays a significant role in advancing their opto-electrical performance of photodetector.

We fabricated MoS2/n-type GaN 2D/3D heterojunction diode, investigated its structural properties and temperature-dependent current–voltage (I–V) characteristics. The MoS2 2D film on GaN is 5.2-nm-thick with ~ 0.64 nm interlayer distance. The Barrier height and ideality factor of the MoS2/n-type GaN heterojunction increase and decrease, respectively with rising temperature, associated with the barrier height inhomogeneities. The barrier height inhomogeneity evaluation considering the Gaussian distribution of barrier heights indicate the presence of double Gaussian barrier distribution with mean barrier heights of 0.95 and 1.44 eV and standard deviations of 0.11 and 0.18 eV in the temperature range of 125–225 and 225–400 K, respectively. Reverse current showed an electric field dependence with the carrier transport dominated by Poole-Frenkel emission irrespective of the temperature.

Au-CuPc nanocomposite films were prepared by simultaneous evaporation of Au and CuPc with various Au and CuPc concentrations. Microstructural analysis of Au-CuPc films revealed elongated Au cluster formation from isolated Au nanoclusters with increasing Au concentration associated with coalescence of Au clusters. Au-CuPc films with different compositions were employed as interlayer in Al/n-Si Schottky diode. Barrier height and series resistance of the Al/n-Si Schottky diode with Au-CuPc interlayer decreased with increasing Au concentration. This could be associated with the enhancement of electron tunneling between neighboring clusters due to decrease in spacing of Au clusters and formation of conducting paths through the composite material. Interface state density of the Al/n-Si Schottky diode with Au-CuPc interlayer increased with increasing Au concentration. This might be because the inclusion of metal decreases the crystallinity and crystal size of the polymer matrix accompanied by the formation of local defect sites at the places of metal nucleation.

The effects of Al and Ti seed layers were studied for undoped and Fe-doped ZnO thin films deposited on n-type Si substrates by electron beam (e-beam) evaporation. The films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The films grown on seed layers showed wurtzite hexagonal crystal nanorod and nanowire structures. A higher angle phase shift was observed in the doped thin films compared to the pristine ZnO films. Microstructural studies confirmed the growth of nanorods and nanowires with average widths of ~32 nm and ~8–29 nm, respectively. The nanostructures were denser and more crystalline on the Al seed layer than on the Ti seed layer for the doped thin films. However, in the undoped thin films, a more crystalline nature was observed on the Ti seeded layer than the Al seeded layer.

A combination of graphene quantum dots and chemically reduced graphene oxide films was obtained by spray-coating their dispersions onto an indium tin oxide coated polyethylene terephthalate substrate. Herein, the graphene quantum dots played a major role in the absorption of ultraviolet light and generation of carriers, whereas the reduced graphene films acted as the transparent electron pathway network. Consequently, the fabricated structure showed good transparency and flexibility, and achieved noticeable ultraviolet sensing. The facile, inexpensive, and extremely low temperature techniques used can be easily upgraded to a larger scale and are compatible with other substrates. In addition, a combination of reduced graphene oxide and graphene quantum dots offers a potential graphene-based platform for foldable optoelectronic device applications.

High-k rare-earth samarium oxide (Sm 2 O 3 ) films are formed on n-GaN surface and analyzed its compositional properties by XPS measurements. XPS results specify that the Sm 2 O 3 films are formed at the interface. Then, the Au/Sm 2 O 3 /n-GaN MIS junction is prepared with a Sm 2 O 3 as insulating layer and correlated its electrical properties with the Au/n-GaN MS junction. The MIS junction shows highest barrier height ((0.81 eV (I-V)/1.0 eV (C-V)) for MIS junction than the MS junction (0.68 eV (I-V)/0.90 eV (C-V)). Excellent rectifying property is observed with lowest reverse leakage current and higher barrier height for the MIS junction than the MS junction, implying that the Sm 2 O 3 insulating layer effectively modified the barrier height. The barrier heights determined from I-V, Cheung's, Norde and Ψ S –V plot closely matched with each other, suggesting that these techniques are reliable and valid. The estimated interface state density of the MIS junction (1.990 × 10 11 cm −2 eV −1 (E C -0.82 eV)) is lower than the MS junction (9.204 × 10 12 cm −2 eV −1 (E C -0.70 eV)), which demonstrates that the Sm 2 O 3 insulating layer performs an important role in lowering the interface state density. The frequency-dependent characteristics of the MS and MIS junctions are discussed in the frequency range of 10 kHz to 1 MHz and found that the determined capacitance values decrease with increasing frequency. The forward I-V characteristic of the MS and MIS junctions reveals the ohmic behavior at low voltage regions and space-charge-limited conduction at higher voltage regions. Results reveal that the reverse leakage current in the studied MS and MIS junctions is controlled by a Poole-Frenkel emission.

An investigation of the electrical and microstructural properties of gold (Au)/p-type silicon (Si) contact was performed as a function of rapid thermal annealing (RTA) temperatures. Au films reacted with Si and produced Au2Si and Au3Si phases during the deposition of the films at room temperature. The electrical properties of the Au contact to p-type Si degraded with increasing RTA temperature. Such a degradation of the electrical properties could be associated with the degradation of the surface and interface morphology caused by the formation of Au-silicide clusters. The RTA process at 500 °C led to an increase in the size of the Au-silicide Island. This led to the further degradation of the electrical properties after annealing at 500 °C.

Recently, significant progress has been made in increasing the figure-of-merit (ZT) of various nanostructured materials, including thin-film and quantum dot superlattice structures. Studies have focused on the size reduction and control of the surface or interface of nanostructured materials since these approaches enhance the thermopower and phonon scattering in quantum and superlattice structures. Currently, bismuth-tellurium-based semiconductor materials are widely employed for thermoelectric (TE) devices such as TE energy generators and coolers, in addition to other sensors, for use at temperatures under 400 K. However, new and promising TE materials with enhanced TE performance, including doped zinc oxide (ZnO) multilayer or superlattice thin films, are also required for designing solid-state TE power generating devices with the maximum output power density and for investigating the physics of in-plane TE generators. Herein, we report the growth of Al2O3/ZnO (AO/ZnO) superlattice thin films, which were prepared by atomic layer deposition (ALD), and the evaluation of their electrical and TE properties. All the in-plane TE properties, including the Seebeck coefficient (S), electrical conductivity (σ), and thermal conductivity (κ), of the AO/ZnO superlattice (with a 0.82 nm-thick AO layer) and AO/ZnO films (with a 0.13 nm-thick AO layer) were evaluated in the temperature range 40-300 K, and the measured S, σ, and κ were -62.4 and -17.5 μV K-1, 113 and 847 (Ω cm)-1, and 0.96 and 1.04 W m-1 K-1, respectively, at 300 K. Consequently, the in-plane TE ZT factor of AO/ZnO superlattice films was found to be ∼0.014, which is approximately two times more than that of AO/ZnO films (ZT of ∼0.007) at 300 K. Furthermore, the electrical power generation efficiency of the TE energy generator consisting of four couples of n-AO/ZnO superlattice films and p-Bi0.5Sb1.5Te3 (p-BST) thin-film legs on the substrate was demonstrated. Surprisingly, the output power of the 100 nm-thick n-AO/ZnO superlattice film/p-BST TE energy generator was determined to be ∼1.0 nW at a temperature difference of 80 K, corresponding to a significant improvement of ∼130% and ∼220% compared to the 100 nm-thick AO/ZnO film/p-BST and n-BT/p-BST film generators, respectively, owing to the enhancement of the TE properties, including the power factor of the superlattice film.

Various boron (B) diffusion techniques are being investigated to fabricate n-type Si solar cells. Thermal oxidation is often used to remove boron-rich layer (BRL) formed as a byproduct of B diffusion because BRL interferes with surface passivation of boron emitter. However, oxidizing the BRL can cause significant degradation in bulk lifetime. In this paper, high resolution electron microscopy (HREM) was performed to detect the presence of BRL after B diffusion and its removal after subsequent oxidation. In addition, bulk lifetime of n-type Si with BRL was measured after various oxidation conditions to systematically investigate the mechanism of oxidation-induced lifetime degradation in n-type Si. Detailed analysis of the oxidized samples revealed that iron (Fe) is primary metal impurity responsible for the bulk lifetime degradation after oxidation. This happens because Fe is gettered in BRL after B diffusion and during the oxidation, when the BRL is consumed, Fe is released into the bulk to degrade lifetime.

An appropriate solution is suggested for synthesizing wafer-scale, continuous, and stoichiometric MoS2 layers with spatial homogeneity at the low temperature of 450 °C. It is also demonstrated that the MoS2 -based visible-light photodetector arrays are both fabricated on 4 inch SiO2 /Si wafer and polyimide films, revealing 100% active devices with a narrow photocurrent distribution and excellent mechanical durability.

We investigated the electrical properties of chemical vapor deposition-grown monolayer graphene/n-type germanium (Ge) Schottky barrier diodes (SBD) using current–voltage ( I–V ) characteristics and low frequency noise measurements. The Schottky barrier parameters of graphene/n-type Ge SBDs, such as Schottky barrier height ( Ф B ), ideality factor ( n ), and series resistance ( R s ), were extracted using the forward I–V and Cheung's methods. The Ф B and n extracted from the forward ln (I)–V plot were found to be 0.63 eV and 1.78, respectively. In contrast, from Cheung method, the Ф B and n were calculated to be 0.53 eV and 1.76, respectively. Such a discrepancy between the values of Ф B calculated from the forward I–V and Cheung's methods indicated a deviation from the ideal thermionic emission of graphene/n-type Ge SBD associated with the voltage drop across graphene. The low frequency noise measurements performed at the frequencies in the range of 10 Hz–1 kHz showed that the graphene/n-type Ge SBD had 1/f γ frequency dependence, with γ ranging from 1.09 to 1.12, regardless of applied forward biases. Similar to forward-biased SBDs operating in the thermionic emission mode, the current noise power spectral density of graphene/n-type Ge SBD was linearly proportional to the forward current.

We report on the co-diffused bifacial N-type solar cells based on N-type Si wafers using the process of spin on doping (SOD, phosphorous source) and boron tribromide (BBr₃) diffusion by atmospheric pressure chemical vapor deposition (APCVD). For bifacial co-diffusion, a phosphorous layer was deposited by SOD on the rear side of N-type Si wafer and a BBr₃ as boron dopant source deposited by APCVD. Co-diffusion process was controlled by changing the flowrate of carrier N₂ gas and drive-in temperatures. It was found that the fabricated bifacial co-diffused N-type solar cell with 2% H₃PO₄ doping, the flowrate of N₂ carrier gas of 15 slm and drive-in temperature at 930°C exhibited the highest conversion efficiency of 15.8% with high open circuit voltage (V(oc)) of 593 mV. As compared to high H₃PO₄ concentrations (5% and 9%), the low H₃PO₄ concentration of SOD showed the higher sheet resistance and decreased in the thickness of N + emitter layer, resulting in the high V(oc), shunt resistance, fill factor and conversion efficiency of solar cells.

A surge in interest of oxide-based materials is testimony for their potential utility in a wide array of device applications and offers a fascinating landscape for tuning the functional properties through a variety of physical and chemical parameters. In particular, selective electronic/defect doping has been demonstrated to be vital in tailoring novel functionalities, not existing in the bulk host oxides. Here, an extraordinary interstitial doping effect is demonstrated centered around a light element, boron (B). The host matrix is a novel composite system, made from discrete bulk LaAlO3:LaBO3 compounds. The findings show a spontaneous ordering of the interstitial B cations within the host LaAlO3 lattices, and subsequent spin-polarized charge injection into the neighboring cations. This leads to a series of remarkable cation-dominated electrical switching and high-temperature ferromagnetism. Hence, the induced interstitial doping serves to transform a nonmagnetic insulating bulk oxide into a ferromagnetic ionic–electronic conductor. This unique interstitial B doping effect upon its control is proposed to be as a general route for extracting/modifying multifunctional properties in bulk oxides utilized in energy and spin-based applications.

Effects of the thickness of copper phthalocyanine (CuPc) film (2, 5, 10, 15, 20, 30 and 40 nm) on the surface morphology, optical and electrical properties of Au/CuPc/n-Si heterojunction have been investigated. The optical band gap of CuPc film was increased with increase in the thickness of the CuPc film. The electrical properties of the Au/n-Si Schottky junction and Au/CuPc/n-Si heterojunctions were characterized by current–voltage (I–V) and capacitance–voltage (C–V) measurements. The barrier height, ideality factor and series resistance were estimated based on the I–V, Cheung’s and Norde’s methods. The barrier heights increased with increasing CuPc interlayer thickness up to 15 nm and remained constant for thickness above 20 nm, associated with the incapability of the generated carriers to reach the interface. The discrepancy in the barrier heights obtained from I–V and C–V measurements indicates the presence of barrier inhomogeneity at the interface as evidenced by higher ideality factor values. It can be concluded that the electrical properties of Au/n-Si Schottky junction can be significantly altered with the variation of CuPc thickness as interlayer.

The electrical characteristics of Al/strained Si-on-insulator (sSOI) Schottky diode have been investigated using current–voltage ( I–V ) and capacitance–voltage ( C–V ) measurements in the wide temperature range of 200–400 K in steps of 25 K. It was found that the barrier height (0.57–0.80 eV) calculated from the I–V characteristics increased and the ideality factor (1.97–1.28) decreased with increasing temperature. The barrier heights determined from the C–V measurements were higher than those extracted from the I–V measurements, associated with the formation of an inhomogeneous Schottky barrier at the interface. The series resistance estimated from the forward I–V characteristics using Cheung and Norde methods decreased with increasing temperature, implying its strong temperature dependence. The observed variation in barrier height and ideality factor could be attributed to the inhomogeneities in Schottky barrier, explained by assuming Gaussian distribution of barrier heights. The temperature-dependent I–V characteristics showed a double Gaussian distribution with mean barrier heights of 0.83 and 1.19 eV and standard deviations of 0.10 and 0.16 eV at 200–275 and 300–400 K, respectively. From the modified Richardson plot, the modified Richardson constant were calculated to be 21.8 and 29.4 A cm −2 K −2 at 200–275 and 300–400 K, respectively, which were comparable to the theoretical value for p-type sSOI (31.6 A cm −2 K −2 ).

In this paper, the carrier transport mechanism at the metal/amorphous hafnium-indium-zinc oxide (a-HIZO) interface was investigated. The contact properties were found to be predominantly affected by the degree of interfacial reaction between the metals and a-HIZO; that is, a higher tendency to form metal oxide phases leads to excellent Ohmic contact via tunneling, which is associated with the generated donor-like oxygen vacancies. In this case, the Schottky-Mott theory is not applicable. Meanwhile, metals that do not form interfacial metal oxide, such as Pd, follow the Schottky-Mott theory, which results in rectifying Schottky behavior. The Schottky characteristics of the Pd contact to a-HIZO can be explained in terms of the barrier inhomogeneity model, which yields a mean barrier height of 1.40 eV and a standard deviation of 0.14 eV. The work function of a-HIZO could therefore be estimated as 3.7 eV, which is in good agreement with the ultraviolet photoelectron spectroscopy (3.68 eV). Our findings will be useful for establishing a strategy to form Ohmic or Schottky contacts to a-HIZO films, which will be essential for fabricating reliable high-performance electronic devices.

We report on the optoelectronic characterization of Ge p–i–n infrared photodetector fabricated on Ge-on-Si substrate using rapid thermal chemical vapor deposition (RTCVD). The phosphorous doping concentration and the root mean square (RMS) surface roughness of epitaxial layer was estimated to be 2 × 1018 cm–3 and 1.2 nm, respectively. The photodetector were characterized with respect to their dark, photocurrent and responsivities in the wavelength range of 1530–1630 nm. At 1550 nm wavelength, responsivity of 0.32 A/W was measured for a reverse bias of 1 V, corresponding to 25% external quantum efficiency, without an optimal antireflection coating. Responsivity drastically reduced from 1560 nm wavelength which could be attributed to decreased absorption of Ge at room temperature.

A Ru/V/n-InP Schottky barrier diode (SBD) is fabricated and investigated its electrical and structural properties as a function of annealing temperature. Measurements showed that the barrier height (BH) of the as-deposited Ru/V/n-InP SBD is found to be 0.83 eV (I–V) and 1.03 eV (C–V). Experimental results indicate that the SBD with high BH and low ideality factors (0.87 eV (I–V), 1.20 eV (C–V), and 1.12) can be achieved after annealing at 400 °C for 1 min in N2 atmosphere. Further, it is observed that the BH slightly decreases to 0.85 eV (I–V) and 1.09 eV (C–V) upon annealing at 500 °C. The BH, ideality factor and series resistance are also determined by Cheung’s functions and Norde method. Further, the energy distribution of interface state density of Ru/V/n-InP SBD is calculated from the forward bias I–V characteristics as a function of annealing temperature. It is found that the interface state density decreases upon annealing at 400 °C and then slightly increases after annealing at 500 °C. The AES and XRD results revealed that the formation of indium phases at the Ru/V/n-InP interface could be the reason for the increase of BH upon annealing at 400 °C. The formation of phosphide phases at the interface may be the cause for the decrease of BH after annealing at 500 °C. The overall surface morphology of Ru/V Schottky contacts is considerably smooth at elevated temperatures.

Electrical properties of Au/n-GaN Schottky rectifier with copper pthalocyanine (CuPc) interlayer were investigated using current–voltage ( I–V ), capacitance–voltage ( C–V ) and conductance–voltage ( G–V ) characteristics. The barrier height obtained for the Au/CuPc/n-GaN Schottky diode was higher than that of the Au/n-GaN Schottky diode. This could be associated with the presence of the CuPc interlayer influencing the space-charge region of the Au/n-GaN structure. The Au/CuPc/n-GaN Schottky structure exhibits higher ideality factor, indicating the higher interface inhomogeneity in Au/CuPc/n-GaN as compared to Au/n-GaN Schottky structure. The density of interface states was extracted using I–V , C–V , and G–V characteristics. The results showed that the introduction of CuPc interlayer facilitated the reduction of interface state density ( N SS ) of Au Schottky contact to n-GaN. Particularly, the N SS obtained from frequency-dependent C–V characteristics was lower than that determined from forward I–V characteristics, which could be attributed to the inhomogeneous distribution of N SS at Schottky interface.

The temperature dependence of the current-voltage (I-V) and capacitance-voltage (C-V) characteristics of an Au/n-type Si Schottky barrier diode (SBD) with a PEDOT:PSS interlayer was investigated. The SBD parameters, such as Schottky barrier height ()B), ideality factor (n), saturation current (I0), doping concentration (ND), and series resistance (Rs), were obtained as a function of temperature. The Richardson constant (A**) obtained from the In(Io/T 2 ) versus 1000/T plot was much less than the theoretical value for n-Si. The mean Schottky barrier height ( � � bo) and standard deviation (·0) calculated using the apparent Schottky barrier height ()ap) versus 1/2kT plot were 1.26eVand 0.15eV, respectively. From a fit of the modified Richardson plot of ln(I0/T 2 ) ¹ (q·) 2 /2(kT) 2 versus 1000/T, the A** was extracted as 134A/cm 2 K 2 , which was close to the theoretical value of the n-Si. The interface state densities obtained from the Au/PEDOT:PSS/n-Si SBD decreased with increasing temperature. Furthermore, the conduction mechanism dominating the reverse-bias leakage current in Au/PEDOT:PSS/n-Si SBD was described and discussed. [doi:10.2320/matertrans.M2014263]

We investigated the effect of bath temperature and electrodeposition potential on the microstructural and chemical properties of ZnO films formed on Mo-coated soda-lime glass substrates using electrodeposition. The electrodeposition was performed using an electrolytic solution containing 0.05 M Zn(NO3)2 for 6 min. The ZnO islands grew larger to impinge with other islands until the bath temperature was increased up to 40 degrees C, above which continuous ZnO film was eventually formed. An increase in the electrodeposition potential resulted in enhancement of the growth rate of the electrodeposited ZnO film with the facilitation of film texturation. The c-axis was perpendicular to surface, which could be associated with the preferential orientation along the (002) direction. At the electrodeposition potential of -1.3 V (vs. a saturated calomel electrode), significant amounts of hydrogen bubbles that electrochemically evolved near the surface of the working electrode hampered the homogenous growth of the ZnO film, which could be responsible for morphological degradation of the ZnO film.

Large-scale 2D single-crystalline copper nanoplates (Cu NPLs) are synthesized by a simple hydrothermal method. The combination of a mild reductant, stabilizer, and shape modifier allows the dimensional control of the Cu nanocrystals from 1D nanowires (NWs) to 2D nanoplates. High-resolution transmission electron microscopy (HR-TEM) reveals that the prepared Cu NPLs have a single-crystalline structure. From the X-ray photoelectron spectroscopy (XPS) analysis, it is found that iodine plays an important role in the modification of the copper nanocrystals through the formation of an adlayer on the basal plane of the nanoplates. Cu NPLs with an average edge length of 10 μm are successfully synthesized, and these Cu NPLs are the largest copper 2D crystals synthesized by a solution-based process so far. The application of the metallic 2D crystals as a semitransparent electrode proves their feasibility as a conductive filler, exhibiting very low sheet resistance (0.4 Ω ▫-1 ) compared to Cu NWs and a transmittance near 75%. The efficient charge transport is due to the increased contact area between each Cu NPL, i.e., so-called plane contact (2D electrical contact). In addition, this type of contact enhances the current-carrying capability of the Cu NPL electrodes, implying that the large-size Cu NPLs are promising conductive fillers for printable electrode applications.

The electrical and transport properties of rare-earth Y2O3 on n-type GaN with Au electrode have been investigated by current–voltage and capacitance–voltage techniques at room temperature. The Au/Y2O3/n-GaN metal-insulator-semiconductor (MIS) diode shows a good rectification behavior compared to the Au/n-GaN metal–semiconductor (MS) diode. Statistical analysis showed that a mean barrier height (BH) and ideality factor are 0.78 eV and 1.93, and 0.96 eV and 2.09 for the Au/n-GaN MS and Au/Y2O3/n-GaN MIS diodes, respectively. Results indicate that the high BH is obtained for the MIS diode compared to the MS diode. The BH, ideality factor and series resistance are also estimated by Cheung’s function and Norde method. From the forward current–voltage data, the interface state density (N SS) is estimated for both the MS and MIS Schottky diodes, and found that the estimated N SS is lower for the MIS diode compared to the MS diode. The results reveal that the introduction of Y2O3 interlayer facilitated the reduction of N SS of the Au/n-GaN interface. Experimental results suggest that the Poole–Frenkel emission is a dominant conduction mechanism in the reverse bias region of both Au/n-GaN MS and Au/Y2O3/n-GaN MIS diodes.

The electrical characteristics of a Pt/n-type Ge Schottky diode with a pyronine-B (PYR-B) interlayer prepared by spin coating was investigated by current–voltage (I–V) and capacitance–voltage (C–V) measurements. It was observed that the barrier height of Pt/PYR-B/n-type Ge (0.65 eV) was higher than that of the conventional Pt/n-type Ge Schottky diode (0.58 eV). This is attributed to the fact that the organic interlayer increases the effective barrier height by influencing the space-charge region of Ge. The introduction of the PYR-B interlayer led to a reduction of the interface state density in the Pt Schottky contact to n-type Ge. The electric field dependence of the reverse leakage current revealed that Schottky emission and Poole–Frenkel emission mechanisms dominated the reverse current in the Pt/n-type Ge and Pt/PYR-B/n-type Ge Schottky diodes, respectively.

We investigate the effect of thermally induced phase transformations on a metastable oxide alloy film, a multiphase Be(x)Zn(1-x)O (BZO), grown on Al2O3(0001) substrate for annealing temperatures in the range of 600-950 °C. A pronounced structural transition is shown together with strain relaxation and atomic redistribution in the annealed films. Increasing annealing temperature initiates out-diffusion and segregation of Be and subsequent nucleation of nanoparticles at the surface, corresponding to a monotonic decrease in the lattice phonon energies and band gap energy of the films. Infrared reflectance simulations identify a highly conductive ZnO interface layer (thicknesses in the range of ≈ 10-29 nm for annealing temperatures ≥ 800 °C). The highly degenerate interface layers with temperature-independent carrier concentration and mobility significantly influence the electronic and optical properties of the BZO films. A parallel conduction model is employed to determine the carrier concentration and conductivity of the bulk and interface regions. The density-of-states-averaged effective mass of the conduction electrons for the interfaces is calculated to be in the range of 0.31 m0 and 0.67 m0. A conductivity as high as 1.4 × 10(3) S · cm(-1) is attained, corresponding to the carrier concentration n(Int) = 2.16 × 10(20) cm(-3) at the interface layers, and comparable to the highest conductivities achieved in highly doped ZnO. The origin of such a nanoscale degenerate interface layer is attributed to the counter-diffusion of Be and Zn, rendering a high accumulation of Zn interstitials and a giant reduction of charge-compensating defects. These observations provide a broad understanding of the thermodynamics and phase transformations in Be(x)Zn(1-x)O alloys for the application of highly conductive and transparent oxide-based devices and fabrication of their alloy nanostructures.

We fabricated interdigitated germanium (Ge) metal-semiconductor-metal photodetectors (MSM PDs) with interdigitated platinum (Pt) finger electrodes and investigated the effects of Pt finger width and spacing on their spectral response. An increase in the incident optical power enhances the creation of electron-hole pairs, resulting in a significant increase in photo current. Lowering of the Schottky barrier could be a main cause of the increase in both photo and dark current with increasing applied bias. The manufactured Ge MSM PDs exhibited a considerable spectral response for wavelengths in the range of 1.53-1.56 μm, corresponding to the entire C-band spectrum range. A reduction in the area fraction of the Pt finger electrode in the active region by decreasing and increasing finger width and spacing, respectively, led to an increase in illuminated active area and suppression of dark current, which was responsible for the improvement in responsivity and quantum efficiency of Ge MSM PDs.

CdSe quantum dots (QDs)-assembled, free-standing TiO2 nanotube arrays (TNTs) are transferred to transparent fluorine-doped tin oxides (FTOs) using a sol-gel process. The TNTs on the FTO (FTO/TNT) not only provide an efficient 1-dimensional electron pathway with few recombination centers, but also allow front side illumination through the transparent FTO, providing a significantly enhanced electron lifetime and light harvesting compared to conventional TNTs on Ti foil and TiO2 nanoparticles-based mesoporous films on the FTO. These effects help improve significantly the short circuit current and open-circuit voltage of quantum dot-sensitized solar cells (QD-SSCs).

CdSe quantum dots (QDs) were deposited on a p-type nanoporous NiO surface by repeating the successive ionic layer adsorption and reaction (SILAR) procedure 6, 9, 12, and 15 times. The NiO/CdSe prepared using 12 SILAR cycles, which is denoted as the NiO/CdSe(12), exhibited a larger QD size and better QD coverage on the nanoporous NiO than the NiO films with CdSe(6) and CdSe(9), leading to better light absorption over longer wavelengths and a significantly increased hole lifetime. The resulting quantum dot-sensitized solar cell (QD-SSC) exhibited significantly enhanced cell efficiency (0.35%) compared to that (0.013%) of the QD-SSC with the NiO/CdSe(6). NiO/CdSe(15), however, exhibited a lower hole lifetime and hindered ion transport as a result of the agglomeration of QDs as well as the severely blocked pores of the nanoporous NiO, causing a significantly reduced cell efficiency for QD-SSCs with NiO/CdSe(15).

The electrical and structural properties of a fabricated W/p-InP Schottky barrier diode (SBD) have been investigated as a function of annealing temperature. The W/p-InP SBD exhibits good rectification behavior. The barrier height (BH) and ideality factor of the W/p-InP SBD are determined to be 0.82 eV (I–V)/0.98 eV (C–V) and 1.34, respectively. However, the BH is increases to 0.87 eV (I–V)/1.08 eV (C–V) after annealing at 300 °C. When the SBD is annealed at 400 °C, the BH decreases to 0.74 eV (I–V)/0.86 eV (C–V) and the ideality factor increases to 1.45. Results indicate that a maximum BH is obtained on the W/p-InP SBD at 300 °C. Norde method is also employed to determine BHs of W/p-InP SBD which are in good agreement with those estimated by the I–V method. Further, Cheung method is used to estimate the series resistance of the W/p-InP SBD, and the consistency is checked using the Norde method. Besides, the energy distribution of interface state density is determined from the forward bias I–V data at different annealing temperatures. Auger electron spectroscopy and X-ray diffraction studies revealed that the formation of W-P interfacial phases at the W/p-InP interface may be the cause for the increase of BH upon annealing at 300 °C. AFM results indicated that the overall surface morphology of the W/p-InP SBD did not change significantly at elevated temperatures.

A new method for growing silicon nanowires is presented. They were grown in an aqueous solution at a temperature of 85 °C under atmospheric pressure by using sodium methylsiliconate as a water-soluble silicon precursor. The structure, morphology, and composition of the as-grown nanowires were characterized by scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectrometry. It was also confirmed by X-ray powder diffraction and Raman spectroscopy that the silicon nanowire has a hexagonal structure. It was possible to grow the crystalline silicon nanowires at low temperature under atmospheric pressure because potassium iodide, which was used as a gold etchant, sufficiently increased the surface energy and reactivity of gold as a metal catalyst for the reaction of the Si precursor even at low temperature.

We have made the successful growth of Ge layer on 8 in. Si (100) substrates by rapid thermal chemical vapor deposition (RTCVD). In order to overcome the large lattice mismatch between Ge and Si, we used a two-step growth method. Our method shows the uniformity of the thickness and good quality Ge layer with a homogeneous distribution of tensile strain and a lower etch pit density (EPD) in order of 105 cm−2. The surface morphology is very smooth and the root mean square (RMS) of the surface roughness was 0.27 nm. The photocurrent spectra were dominated by the Ge layer related transition that corresponding to the transitions of the Si and Ge. The roll-off in photocurrent spectra beyond 1600 nm is expected due to the decreased absorption of Ge.

The temperature dependent electrical characteristics of Se/n-GaN Schottky barrier diode have been investigated in the temperature range of 130–400 K in the steps of 30 K. The estimated barrier height (ϕbo) and ideality factor n are found to be 0.46 eV and 3.83 at 130 K, 0.92 eV and 1.29 at 400 K. The ϕbo and n are found to be strongly temperature dependent and while the ϕbo decreases and the n increase with decreasing temperature. Such behavior of ϕbo and n is attributed to Schottky barrier inhomogeneities, explained by the assumption of Gaussian distribution of barrier heights at the metal/semiconductor interface. Experimental results revealed the existence of a double Gaussian distribution with mean barrier height values of 1.33 and 0.90 eV and standard deviations (σo) of 0.0289 and 0.010 V, respectively. The modified ln(Io/T2) − (q2 σ o 2 /2k2T2) versus 103/T plot gives ϕbo and Richardson constant (A∗) values as 1.30 and 0.88 eV, 23.6 and 19.2 A/cm2 K2 at 400 and 130 K, respectively without using the temperature coefficient of the barrier height. Further, the barrier height obtained from C–V method decreases with an increase in temperature. It is also noted that the barrier height value estimated from the C–V method is higher than that estimated from the I–V method at various temperatures. Possible explanations for this discrepancy are presented. The interface state density (Nss) is found to be decreased with an increasing temperature. The reverse-bias leakage current mechanism of Se/n-GaN Schottky diode is investigated. Both Poole–Frenkel and Schottky emissions are described and discussed.

We investigated the electrical characteristics of Au/n-GaN Schottky rectifier incorporating a copper pthalocyanine (CuPc) interlayer using current­voltage (I­V), capacitance­voltage (C­V) and conductance­voltage (G­V) measurements. The barrier height of the Au/CuPc/n-GaN Schottky contact was higher than that of the Au/n-GaN Schottky diode, indicating that the CuPc interlayer influenced the space charge region of the n-GaN layer. The series resistance of Au/CuPc/n-GaN Schottky contact extracted from the C­V and G­V methods was dependent on the frequency. In addition, the series resistance obtained from C­V and G­V characteristics was comparable to that from Cheung’s method at sufficiently high frequencies and in strong accumulation regions. The forward logI­logV plot of Au/CuPc/n-GaN Schottky contact exhibited four distinct regions having different slopes, indicating different conduction mechanisms in each region. In particular, at higher forward bias, the trap-filled space-charge-limited current was the dominant conduction mechanism of Au/CuPc/n-GaN Schottky contact, implying that the most of traps were occupied by injected carriers at high injection level. [doi:10.2320/matertrans.M2013449]

We have investigated the influence of Be concentration on the microstructure of BexZn1−xO ternary films (from x = 0 to 0.77), grown on Al2O3(0001) substrates using radio-frequency co-sputtering. With increasing Be concentration, the (0002) X-ray diffraction peak shows a systematic shift from 33.86° to 39.39°, and optical spectroscopy shows a blue-shift of the band gap from 3.24 to beyond 4.62 eV towards the deep UV regime, indicating that Be atoms are incorporated into the host ZnO lattice. During the band-gap modulation, structural fluctuations (e.g. phase separation and compositional fluctuation of Be) in the ternary films were observed along with a significant change in the mean grain size. X-ray photoelectron spectroscopy indicates higher concentrations of metallic Be states found in the film with the smaller grain size. Correlation between these two observations indicates that Be segregates to near grain boundaries. A model structure is proposed through simulation, where an increase in grain growth driving force dominates over the Be particle pinning effect. This leads to further coalescence of grains, reactivation of grain growth, and the uniform distribution of Be composition in the BexZn1−xO alloy films.

We investigate the effect of annealing temperature on the electrical and structural properties of Er/p-InP Schottky contacts. The barrier height of as-deposited Er Schottky contacts is found to be 0.89 eV ( I – V ) and 0.98 eV ( C – V ). After annealing at 200 °C, a maximum barrier height is obtained for the Er Schottky contact and the corresponding values are 0.93 eV ( I – V ) and 1.11 eV ( C – V ). However, both I – V and C – V measurements show that the barrier height slightly decreases for the contacts annealed at 300 °C and 400 °C. Norde and Cheung’s methods are used to extract the barrier height, ideality factor, and series resistance of Er/p-InP Schottky contact. The barrier heights obtained from the Norde and Cheung’s methods are closely matched with those obtained from the I – V method. Further, the discrepancy between Schottky barrier heights calculated from I – V and C – V methods is also discussed. Based on the AES and XRD results, the increase or decrease in Schottky barrier heights upon annealing at elevated temperatures could be attributed to the formation of interfacial phases at the Er/p-InP interface vicinity.

Angle-resolved X-ray photoelectron spectroscopy (AR-XPS) and atomic force microscopy (AFM) were employed to investigate the detailed surface bonding structure and morphology of polyethyleneimine (PEI) layers coated on a SiO2 substrate in concentrations of 0.5­ 10.0mass%. With an increase in the PEI concentration, the C­N bonds corresponding to the imine group (­NH) became dominant in the PEI layers, implying a characteristic feature to verify the immobilization of PEI on the SiO2 surface. The thickness of PEI layer calculated using ARXPS gradually increased with increasing PEI concentration up to a maximum 5mass%, above which it became saturated. AFM results showed that an increase in PEI concentration led to a decrease in the root mean square (RMS) roughness of PEI layers. Such a saturation tendency of PEI thickness combined with the strongly dependence of the surface morphology behavior of PEI layers on the PEI concentration indicated that SiO2 surface was fully covered by monolayer PEI with a smooth surface morphology at PEI concentration in excess of 5mass%. [doi:10.2320/matertrans.M2014013]

A transient voltage suppression (TVS) diode with abrupt junctions was fabricated using low-temperature epitaxy. The effect of electrostatic discharge (ESD) stress on the reverse leakage current conductive mechanism of the TVS diode was investigated using IEC61000-4-2 (IEC) standard analysis, in accordance with temperature-dependent current-voltage (I-V) characteristics. The fabricated TVS diode showed excellent ESD robustness, with negligible degradation up to «19.5 kV and failure at «20 kV stress. The ESD stress evidently led to the generation of shallow and deep defect states in the depletion region located 0.52­1.08 eV below the conduction band, and these states served as a main contributor to the resulting reverse leakage current. In devices to which IEC peak voltage stresses of less than «19.5 kV had been applied, reverse conduction was dominated by generation-recombination current; the application of the «20 kV failure stress caused reverse conduction to become dominated by a combination of tunneling current via deep defects and Poole-Frenkel barrier lowering. The proposed TVS can serve as a highly stable and reliable ESD protector of electronic components, serving an evolving need in nanoscale technology. [doi:10.2320/matertrans.M2014214]

A pin photo-diode was fabricated from the p-Ge/i-Ge/n-Si hetero junction structure grown by using rapid thermal chemical vapor deposition (RTCVD). The structural properties of the p-Ge/i-Ge/n-Si hetero junction structure were investigated using high-resolution X-ray diffraction (HRXRD). Specifically, the recent advances in the dry etching of p-Ge/i-Ge/n-Si hetero junction structure have been used to define pin photo-diode p-Ge/i-Ge layer mesas. I–V characteristics of the pin photo-diode indicate a reasonable reverse saturation current of 96 μA at −1 V and a high reverse breakdown voltage in excess of −100 V. The photocurrent with a responsivity of 0.19 A/W at the wavelength of 1.55 μm is flat over a wide range of reverse bias voltage and the leakage currents is 700 nA at a reverse 0.1 V bias voltage. The roll-off in photocurrent spectra after wavelength of 1600 nm is expected due to the decreased absorption of Ge at room temperature.