Thermal annealing behaviour on Schottky barrier parameters and structural properties of Au contacts to n-type GaN

We have investigated the thermal annealing effects on electrical and structural properties of Au Schottky contacts on n-type GaN using current–voltage (I–V), capacitance–voltage (C–V), X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) measurements. The calculated Schottky barrier height of the as-deposited Au/n-GaN diode was 0.85 eV (I–V) and 1.4 eV (C–V), respectively. However, after annealing at 300 °C it was found that the Schottky barrier height (SBH) slightly decreased to 0.77 eV (I–V) and 1.24 eV (C–V), and then slightly increased to 0.83 eV (I–V) and 1.30 eV (C–V) when the contact was annealed at 400 °C. With further increase in annealing temperature to 500 °C the barrier height was decreased and the respective values are 0.73 eV (I–V) and 1.02 eV (C–V). Based on the X-ray diffraction and RBS results, the formation of gallide phases at the Au/n-GaN interface could be the reason for variation in the Schottky barrier heights upon annealing temperatures.     

Electrical conductivity of polyaniline doped PVC-PMMA polymer blends

The electrical conductivity of polyaniline doped polyvinylchloride (PVC) and poly(methyl methacrylate) (PMMA) thin films has been measured by studying the I–V characteristics at various temperatures in the range 323–363 K. The results are presented in the form of I–V characteristics and analysis has been made by interpretation of Poole-Frenkel, Fowler-Nordheim, Schottky ln(J) vs T plots, Richardson and Arrhenius plots. The analysis of these results suggests that Schottky and Richardson mechanisms are primarily responsible for the observed conduction.     

Photoresponse of n -ZnO/ p -Si heterojunction towards ultraviolet/visible lights: thickness dependent behavior

A series of n-ZnO/p-Si thin film heterojunctions have been fabricated by a low cost sol–gel technique for different ZnO film thicknesses and the dark as well as photo current–voltage (I–V) characteristics have been investigated in details. The heterojunction with ZnO thickness of 0.46 μm shows the best diode characteristics in terms of rectification ratio, I _F/I _R = 5.7 × 10³ at 5 V and reverse leakage current density, J _R = 7.6 × 10⁻⁵ A cm⁻² at −5 V. From the photo I–V curves and wavelength dependent photocurrent of the heterojunctions, it is found that the junction with 0.46 μm ZnO thickness shows the highest sensitivity towards both UV and visible lights.     

Optical and photovoltaic properties of silicon wire solar cells with controlled ZnO nanorods antireflection coating

We introduce a new type of silicon micro-wire (SiMW) solar cell with a conformal zinc oxide (ZnO) nanorods anti-reflection coating (ARC) and discuss the optical and photovoltaic properties of the SiMW solar cells with controlled ZnO nanorods. The fabrication processes were composed of metal-assisted electroless etching combined with photolithography, spin-on-dopant diffusion, and hydrothermal synthesized ZnO nanorods growth. We found that the combination of Si wire geometry and ZnO ARC was able to maximize the light absorption and to minimize the light reflectance. Illuminated current–voltage (I–V) results show that the photovoltaic efficiency of SiMW solar cells with optimized ZnO ARC was enhanced more than 50% and the short-circuit current density was improved by over 43% compared to SiMW solar cells without ZnO ARC. This is mainly attributed to the reduced light reflectance and enhanced photon absorption. These hybrid structures are promising for making low-cost Si wire solar cells and making them applicable to photovoltaic devices with large areas.     

Thermodynamic and quasi-chemical modeling of point defects in CdTe〈I〉

The carrier concentration and the densities of predominant point defects in CdTe〈I〉 crystals have been calculated as functions of two-step annealing parameters using quasi-chemical and thermodynamic modeling. We have identified the dominant native and impurity defect species, which govern the electrical properties of the material, and proposed a compensation model that takes into account not only native defects, I_Te⁺ substitutional defects, and their complexes with native point defects, such as (V _Cd²⁻I_Te⁺)⁻, and (V _Cd²⁻2I_Te⁺)⁰, but also DX ⁻ centers. The equilibrium constants of formation of the V _Cd²⁻I_Te⁺)⁻, defect complex and center have been evaluated.     

Fabrication and characterization of ZnO film based UV photodetector

ZnO films were deposited on Al₂O₃ substrates by metalorganic chemical vapor deposition (MOCVD) at temperatures of 400, 450 and 500 °C. The photoconductivity of the films has been analyzed for ultraviolet detector application. The changes in photoresponse and current–voltage (I–V) are correlated with the deposition temperatures and microcrystalline structures. The study suggested that the photoresponse originating from bulk- and surface-related processes. For a film deposited at 400 °C, a 1 ms fast rising time and a 5 ms fall time were observed. The photoresponsivity is ∼24 A/W with a 3 V bias.     

Study of the effect of thermal annealing on high k hafnium oxide thin film structure and electrical properties of MOS and MIM devices

The effect of rapid thermal annealing on structural and electrical properties of high k HfO₂ thin films is investigated. The films were initially deposited at pre-optimized sputtering voltage of 0.8 kV and substrate bias of 80 V in order to get optimized results for oxide charges and leakage current as a MOS device. The film properties were investigated for optimum annealing temperature in oxygen and optimum rapid thermal annealing temperature in nitrogen respectively to get the best electrical results as a MOS device structure. The film thickness, composition and microstructure is studied by Laser Ellipsometry, XRD and AFM and the effect of thermal annealing is shown. The electrical I–V and C–V characteristics of the annealed dielectric film were investigated employing Al-HfO₂-Si MOS capacitor structure. The flat-band voltage (V _fb) and oxide-charge density (Q _ox) were extracted from the high-frequency C–V curve. Dielectric study were further carried out on HfO₂ thin films having metal–insulator–metal (MIM) configuration over a wide temperature (300–500 K) and frequency (100 Hz to 1 MHz) range.     

Electrical behavior of low density polyethylene containing an inhomogeneous distribution of ZnO nanoparticles

ZnO nanoparticles were mixed with low density polyethylene (LDPE) to form nanocomposites. The distribution of ZnO filler particles was controlled by changing the mixing method, and the effects of controlled inhomogeneous distribution on the electrical resistivity were measured. The percolation limit in the composites with controlled inhomogeneity decreased significantly compared to that of the analogous nanocomposites with uniform filler distributions, and the resistivity of the filled composites decreased as a function of applied field strength, exhibiting a nonlinear I–V relationship. The nonlinearity increased with ZnO filler concentration.     

Study of electrical and microstructure properties of high dielectric hafnium oxide thin film for MOS devices

Hafnium oxide (HfO₂) has emerged as the most promising highkdielectric for MOS devices. As-deposited sputtered HfO₂ thin films have large number of defects resulting in increased oxide charge and leakage current. In this paper the effect of sputtering voltage, bias sputtering and post deposition thermal annealing is investigated. The I–V and C–V characteristics of the dielectric film are studied employing Al–HfO₂–Si MOS capacitor structure. It is found that oxide charge increases with increasing sputtering voltage. Thermal annealing in oxygen reduces the interface/oxide charges and leakage current. It is shown that applying substrate bias during film deposition leakage current is further reduced by an order of magnitude. The microstructure of thin film is examined by AFM. The reduction in surface roughness with bias sputtering is shown. The experimental results are presented and discussed for device application.     

Electric and dielectric properties of solution-gas interface-grown PbS films

Dielectric properties andI–V characteristics of solution-gas interface-formed PbS thin-film capacitors (Al/PbS/Al) of various thicknesses have been studied in the frequency range 10-10⁶ Hz at various temperatures (300–443 K). Current-voltage (I–V) characteristics show space-charge-limited conduction. Dielectric constant (ε) increases with increasing film thickness and temperature and decreases with increase of frequency. The loss factor (tanδ) peaks observed in tanδ vs frequency and tanδ vs temperature reveal relaxation effect from dipolar orientation. These maxima shift to higher-temperature region with increasing frequency. The large increase in capacitance (C) and dielectric constant (ε) towards low-frequency (f) region indicates the possibility of an interfacial polarization mechanism in this region.     

Size variation of polyaniline nanoparticles dispersed in polyvinyl alcohol matrix

We report the preparation of polyaniline (PANI) nanoparticles dispersed in polyvinyl alcohol (PVA) matrix. From SEM picture it is seen that the particle sizes vary from 100–20 nm. Also with increase in PVA content the stability of dispersion is found to increase. Apart from SEM, spin cast films of PANI in PVA are also characterized through XRD and FTIR. XRD shows increase in crystallinity with PVA content and FTIR gives evidence of crosslinking between PANI and PVA molecules. In plane electrical conductivity (in the range of 10² Scm⁻¹) and the exponent of nonlinear I–V are found to decrease with increase of PVA content. There is a good correlation between SEM, XRD, FTIR and electrical properties.     

The influence of rapid thermal annealing on electrical and structural properties of Pt/Au Schottky contacts to n-type InP

The electrical and structural properties of Pt/Au Schottky contacts to n-InP have been investigated in the annealing temperature range of 200–500 °C by current–voltage (I–V), capacitance–voltage (C–V), Auger electron spectroscopy (AES) and X-ray diffraction (XRD) measurements. The barrier height of as-deposited Pt/Au Schottky contact is found to be 0.46 eV (I–V) and 0.68 eV (C–V). For the contacts annealed at 300 °C, the barrier height is increased to 0.51 eV (I–V) 0.89 eV (C–V). Further increase in annealing temperature up to 500 °C, the barrier height has been found to decrease to 0.49 eV (I–V) 0.82 eV (C–V) from those values obtained at 300 °C. It has been found that the electrical characteristics are significantly improved for Pt/Au Schottky contacts upon annealing at 300 °C. Based on the Auger electron spectroscopy and X-ray diffraction results, the formation of Pt–In and Au–In intermetallic compounds at the interface may be the reason for the increase of barrier height after annealing at 300 °C for Pt/Au Schottky contacts. From the atomic force microscopy (AFM) results, it is evident that the surface becomes smooth with RMS roughness of 16.91 nm for the Pt/Au Schottky contacts after annealing at 500 °C compared to the 300 °C annealed sample (RMS roughness of 17.33 nm).     

High field electrical behaviour in lithium-phospho-vanadate glass system

The high field electrical switching behaviour of lithium-phospho-vanadate glasses has been studied by determining the current-voltage characteristics. The investigated glasses exhibit temperature, thickness and composition dependent trends. At low current, the I–V characteristics obey Ohm’s law followed by a negative resistance region where the bulk behaviour dominates and at higher values of current the sample goes to a low resistance state. The studied glasses exhibit memory type switching. It is suggested that electrical switching is due to the formation of conducting channels that are due to electronic origin while thermal effects dominate once the channels are formed resulting in crystallization.     

Effect of annealing temperature on electrical and nano-structural properties of sol–gel derived ZnO thin films

Zinc oxide (ZnO) thin films have been prepared on silicon substrates by sol–gel spin coating technique with spinning speed of 3,000 rpm. The films were annealed at different temperatures from 200 to 500 °C and found that ZnO films exhibit different nanostructures at different annealing temperatures. The X-ray diffraction (XRD) results showed that the ZnO films convert from amorphous to polycrystalline phase after annealing at 400 °C. The metal oxide semiconductor (MOS) capacitors were fabricated using ZnO films deposited on pre-cleaned silicon (100) substrates and electrical properties such as current versus voltage (I–V) and capacitance versus voltage (C–V) characteristics were studied. The electrical resistivity decreased with increasing annealing temperature. The oxide capacitance was measured at different annealing temperatures and different signal frequencies. The dielectric constant and the loss factor (tanδ) were increased with increase of annealing temperature.     

ZnO/Si solar cell fabricated by spray pyrolysis technique

The ZnO/Si heterojunctions have been prepared by depositing n-ZnO films doped with aluminium on p-Si by spray pyrolysis method. Heterojunction solar cells were fabricated using the configuration Al/ZnO/Si/In. The electrical properties of the heterojunction are investigated by means of current–voltage measurements in the temperature range 295–375 K. The cells show the rectifying behaviour characterized by the current–voltage (I–V) measurement under a dark condition, while photoelectric effects have been exhibited under the illumination. As a result, the conversion efficiency of the fabricated cell of about 6.6% was obtained.     

Fabrication and comparative study of top-gate and bottom-gate ZnO–TFTs with various insulator layers

Transparent ZnO thin film transistors (ZnO–TFTs) with different structures and dielectric layers were fabricated by rf magnetron sputtering. The PbTiO₃, AlO _x , SiN _x and SiO _x films were attempted to serve as the gate dielectric layers in the devices, respectively, and XRD was employed to investigate the crystal structure of ZnO films deposited on these dielectric layers. The optical properties of transparent TFTs were measured and revealed the average transmittance ranged from 60 to 80% in the visible part of the spectrum. Electrical measurement shows the properties of the ZnO–TFTs have great relations with the device structure. The bottom-gate TFTs have better behaviors than top-gate ones with the mobility, threshold voltage and the current on/off ratio of 18.4 cm² V⁻¹ s⁻¹, −0.7 V and 10⁴, respectively. The electrical difference of the devices may be due to different character of the interface between the channel and dielectric layers.     

Effect of annealing temperature on electrical characteristics of ruthenium-based Schottky contacts on n-type GaN

The electrical properties of ruthenium (Ru) and ruthenium/gold (Ru/Au) Schottky contacts on n-type GaN are investigated as a function of annealing temperature by current–voltage (I–V) and capacitance–voltage (C–V) techniques. The Schottky barrier height of as-deposited Ru/n-GaN is found to be 0.88 eV (I–V) and 1.10 eV (C–V) respectively. However, after annealing at 500°C for 1 min in the nitrogen ambient, the decrease in barrier height is quite considerable and found to be 0.80 eV (I–V) and 0.86 eV (C–V). In the case of Ru/Au Schottky diode the measured barrier height is 0.75 eV (I–V) and 0.93 eV (C–V). In contrast to the Ru contacts, it is interesting to note that the barrier height of Ru/Au depends on the annealing temperature. Annealing at 300°C improves the barrier height and the corresponding values are 0.99 and 1.34 eV. Further increase in annealing temperature decreases the barrier height and the respective values are 0.72 and 1.08 eV at 500°C. From the above observations, it is clear that the electrical properties of annealed Ru/Au contacts are improved compared to the as-deposited films. However, Ru Schottky contacts exhibit a kind of thermal stability during annealing.     

Binary acceptor doping of epitaxial gallium phosphide for high-temperature electronic devices

We have experimentally studied the reverse-bias branch of the current-voltage (I–U) characteristics of high-temperature two-electrode devices (rectifying diode, Zener diode, hot electron emitter), the technology of which involves the stage of binary zinc-magnesium doping. Factors leading to the development of various types of the avalanche breakdown are analyzed as dependent on the Zn/Mg ratio. Differences in the characteristics and behavior of the I–U curves are related to features of the acceptor diffusion, which always accompanies the process of doping involved in the growth of multilayer epitaxial p–n structures.     

Structural and electrical properties of Ba<Subscript>5</Subscript>SmTi<Subscript>3</Subscript>V<Subscript>7</Subscript>O<Subscript>30</Subscript> ceramics

Polycrystalline sample of Ba₅SmTi₃V₇O₃₀ was prepared by a high-temperature solid-state reaction technique. Structural and microstructural characterizations were performed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). X-ray preliminary structural studies reveal that the material has orthorhombic structure at room temperature. Detailed electrical (dielectric and impedance) properties of the material studied by using a complex impedance spectroscopy (CIS) technique in a wide temperature range (33–450 °C) at different frequencies (10²–10⁶ Hz) reveal that the relative dielectric constant of the material increases with rise in temperature and thus bulk has a major contribution to its dielectric and electrical properties. The bulk resistance of the material decreases with rise in temperature exhibiting a typical negative temperature coefficient of resistance (NTCR) behavior. The nature of the temperature variation of conductivity and value of activation energy, suggest that the conduction process is of mixed-type (ionic–polaronic and space charge). The existence of ferroelectricity in the compound was confirmed from polarization study.     

Investigation of electrical conduction in polyvinyl formal

Current-voltage (I–V) characteristics of pure polyvinyl formal (PVF) were investigated at different fields, range 5–100 kV/cm, as a function of temperature, range 313–363 K. It was observed that while at low fields (up to 25 kV/cm), the conduction was Ohm’s law-dependent at high fields (beyond 25 kV/cm), the conduction was Poole-Frenkel (P-F) mechanism-dependent. An attempt was made to identify the nature of the current by comparing its observed dependence on temperature, electric field and electrode materials with their respective characteristic features of the existing theories of electrical conduction. The current showed a strong dependence on temperature. To identify the possible mechanism of conduction, current versus square root of field characteristics were drawn with aluminium, silver, copper and gold as upper electrodes and Al as the lower electrodes. The observed characteristic suggested that the charge carriers were generated by the field-assisted lowering of coulombic barriers at the traps, and were subsequently conducted through the bulk of the material by a hopping process between the localized states by a Jonscher-Ansari-modified P-F mechanism. The calculated value of the modified P-F barrier was ⋍ 1·94×10⁻¹⁹ J (1·21 eV).