The barrier-height inhomogeneity in identically prepared Ni/n-type 6H-SiC Schottky diodes

The effective barrier heights and ideality factors of identically fabricated Ni/n-type 6 H-SiC Schottky diodes (23 dots) have been calculated from their experimental forward bias current–voltage (I–V) and reverse bias capacitance–voltage (C–V) characteristics. A statistical study related to the experimental barrier heights (BHs) and ideality factors of the diodes has been made. The effective Schottky barrier heights (SBHs) and ideality factors obtained from the I–V and C–V characteristics have differed from diode to diode. The BHs obtained from the I–V characteristics varied from 0.85 to 1.03 eV, the ideality factors varied from 1.13 to 1.40 and the BHs from C^-2–V characteristics varied from 1.10 to 1.70 eV. The experimental BH and ideality factor distributions obtained from the I–V characteristics are fitted by a Gaussian function, and their mean values are found to be 0.92±0.04 eV and 1.29±0.08 eV, respectively. The lateral homogeneous SBH value of 1.16 eV for the Ni/n-type 6H-SiC diodes has been calculated from a linear extrapolation of the effective barrier heights to n_if=1.03. PACS 79.40.+z; 73.40.Sx; 73.30.+y; 71.20.Nr     

Capacitance spectroscopic study of the Si/HF-electrolyte interface

Thep-Si/HF-electrolyte interface was characterized by capacitance–voltage (C–V) and current–voltage (I–V) studies. At low frequency, the measured capacitance exhibits two maxima: one in the weak accumulation regime (around 0.8 V [SCE]) and the other in the strong accumulation regime (around 2.6 V [SCE]), both of which disappear at high frequency. The disappearance of the two capacitance maxima is attributed to the slow response of interface traps to high frequencies. The flat-band potential, V_FB, is found to be frequency dependent. The surface state densities corresponding to the two capacitance maxima are estimated to be 3.2×10¹¹ cm^-2 and 2.4×10¹¹ cm^-2, respectively. The in situ I–V characteristics distinguish pore formation, transition and electropolishing regions. Porous Si synthesized at 50 mA cm^-2 gives a broad photoluminescence peak around 2.04 eV at 300 K. Received: 4 September 2000 / Accepted: 9 February 2001 / Published online: 26 April 2001     

Electroluminescence from ZnO nanowire-based p-GaN/n-ZnO heterojunction light-emitting diodes

Vertically aligned ZnO nanowires were successfully grown on the sapphire substrate by nanoparticle-assisted pulsed laser deposition (NAPLD), which were employed in fabricating the ZnO nanowire-based heterojunction structures. p-GaN/n-ZnO heterojunction light-emitting diodes (LEDs) with embedded ZnO nanowires were obtained by fabricating p-GaN:Mg film/ZnO nanowire/n-ZnO film structures. The current–voltage measurements showed a typical diode characteristic with a threshold voltage of about 2.5 V. Electroluminescence (EL) emission having the wavelength of about 380 nm was observed under forward bias in the heterojunction diodes and was intensified by increasing the applied voltage up to 30 V.     

Fabrication of transparent p-n junction composed of heteroepitaxially grown p-Li<Subscript>0.15</Subscript>Ni<Subscript>0.85</Subscript>O and n-ZnO films for UV-detector applications

Thin films of high-quality p-type Li_0.15Ni_0.85O (LNO) and n-type ZnO were heteroepitaxially grown on MgO(111) substrate by pulsed laser deposition technique to form transparent wide bandgap heterojunctions. The epitaxial nature of this p-LNO/n-ZnO/MgO heterojunction was confirmed to be (111)LNO||(0001)ZnO||(111)MgO (out-of-plane) and (002)LNO||(1002)ZnO||(002)MgO (in-plane) by X-ray diffraction. Optical transmittance spectrum and I–V characteristics were obtained at room temperature. The heterojunction exhibits reasonable optical transmittance of 50–60% on average in the whole infrared and visible region, and highly asymmetric electrical rectification with a turn-on voltage of about 1.0 V and a small leakage current. The highest photoresponsivity for a wavelength of 350 nm is 3.4×10³ V/W when the junction is irradiated under 5 μW UV illumination. The spectral response peak is obtained in the UV region and a reasonable large responsivity is shown for this p-LNO/n-ZnO/MgO heterojunction, which suggests the possibility of an inexpensive transparent oxide UV detector in a wide variety of electronics applications. PACS 68.55.Jk; 81.05.Dz; 81.15.Fg     

Investigation of temperature-dependent electrical properties of p-VOPc/n-si heterojunction under dark conditions

An organic/inorganic heterojunction p-VOPc/n-Si was fabricated and its electrical properties were investigated. Temperature-dependent dark current–voltage (I–V) characteristics of the heterojunction exhibited rectification behaviour with a rectification ratio of 405 at ±1 V and room temperature. The current–voltage characteristics of the cell showed ohmic conduction at low voltages followed by a space charge-limited current (SCLC) conduction dominated by an exponential trap distribution at higher voltages. At room temperature, the series and shunt resistances were found to be approximately 1.4 and 100 kΩ, respectively. Diode ideality factor n was found to be 3.2 at room temperature and dropped to 1.9 at 363 K. Room temperature mobility of vanadyl phthalocyanine (VOPc) was extracted from the I–V characteristics in the SCLC region and was found approximately 15.5 × 10⁻³ cm² V⁻¹ s⁻¹. The effective barrier height, Ф_B, was estimated as 0.77 eV. The effect of temperature, on various heterojunction parameters was recorded under dark conditions and at temperatures ranging from 300 to 363 K.     

The demonstration of hybrid n-ZnO nanorod/p-polymer heterojunction light emitting diodes on glass substrates

We report a demonstration of heterojunction light emitting diode (LED) based on a hybrid n-ZnO-nanorod/p-polymer layered structure. The ZnO was grown using the aqueous chemical growth (ACG) on top of the polymer(s) which were deposited on glass. The current–voltage (I–V) behavior of the heterojunctions showed good rectifying diode characteristics. Room-temperature electroluminescence (EL) spectra of the LEDs provided a broad emission band over a wide LED color range (430–650 nm), in which both zinc and oxygen vacancy peaks are clearly detected. We present here luminescent devices based on the use of ZnO-nanorods in combination with two different blended and multi-layered p-type polymers. Electroluminescence of the first batch of devices showed that white bluish strong emission for the presently used polymers is clearly observed. We obtained a turn-on voltage of 3 V and break-down voltage equal to −6 V for PVK-TFB blended device. The corresponding values for the NPD-PFO multilayer device were 4 V and −14 V, respectively. The rectification factors were equal to 3 and 10 for the two devices, respectively. The films and devices processed were characterized by scanning electron microscopy (SEM), DEKTAK 3ST Surface Profile, Semiconductor Parameter Analyzer, photoluminescence (PL), and electroluminescence (EL).     

Structure and electrical properties of HfO<Subscript>2</Subscript> high-<Emphasis Type="Italic">k</Emphasis> films prepared by pulsed laser deposition on Si (100)

High-k gate dielectric hafnium dioxide films were grown on Si (100) substrate by pulsed laser deposition at room temperature. The as-deposited films were amorphous and that were monoclinic and orthorhombic after annealed at 500°C in air and N₂ atmosphere, respectively. After annealed, the accumulation capacitance values increase rapidly and the flat-band voltage shifts from −1.34 V to 0.449 V due to the generation of negative charges via post-annealing. The dielectric constant is in the range of 8–40 depending on the microstructure. The I–V curve indicates that the films possess of a promising low leakage current density of 4.2×10⁻⁸ A/cm² at the applied voltage of −1.5 V.     

Possible observation of coulomb blockade at room temperature

We have studied the (I–V) characteristics of the tunnel junction formed between the tip and the substrate in an STM at room temperature. We find that in such an arrangement it may be possible to get a junction capacitance ⋍10⁻¹⁹ F and junction conductance <1μs. When the junction conductance is <1μs strong nonlinearity is observed in the (I–V) characteristics. We explain this nonlinearity as onset of coulomb blockade of tunneling electrons.     

Structural,optical and electrical properties of post annealed Mg doped ZnO films for optoelectronics applications

Mg _x Zn_1-x O films with 0.15 mole composition of Magnesium were successfully deposited by the spin coating sol–gel method. Zinc acetate dihydrate and Magnesium acetate were used as starting precursors to prepare the solution in ethanol solvent. The MgZnO films were deposited on microscopic glass substrates and post annealed at three different temperatures. X-ray Diffractometer (XRD), Scanning Electron Microscopy (SEM) and UV–VIS Spectrophotometer were used to characterize the deposited films for studying structural and optical properties. Energy dispersive analysis by X-ray (EDAX) was used to determine incorporation of Mg content in ZnO films. XRD spectrum reveals that, the deposited Mg doped ZnO films were polycrystalline in nature. The intensity of c-axis in the XRD spectrum goes on decreasing as Mg composition slightly increasing corresponding to increase in annealing temperature. EDAX spectra clearly showed the incorporation of Mg into the ZnO films. Semiconductor characterization system was used for the I–V characterization of MgZnO films. I–V characteristics show decrease in current as increase in the biased voltage. Optical band gap of MgZnO films was found to be increased from 3.2 to 3.38 eV as estimated from the absorption coefficients.     

A comprehensive model for the I –V characteristics of metal-Ta 2 O 5 /SiO 2 -Si structures

The I–V characteristics of metal-Ta₂O₅/SiO₂-Si structures are precisely described with a comprehensive model, for both polarities, in the whole measurement range where there is no noticeable degradation and over seven orders of magnitude of the current. Hopping conduction and tunneling were elucidated to be the dominant conduction mechanisms in the SiO₂ layer and Poole–Frenkel internal field-assisted emission in the Ta₂O₅ layer. Other possible relevant mechanisms were discussed and subsequently discarded, based on their minor contribution. Theoretical calculations are made with fitted values of the defect related constants for hopping conduction of SiO₂ and Poole–Frenkel emission of Ta₂O₅ and the thickness of the SiO₂ layer. For gates positively biased, tunneling of electrons from the silicon conduction band through the SiO₂ is considered, while for gates negatively biased, tunneling of holes from the silicon valence band. Approximations for practical use are proposed and thus introduced limitations of the model discussed. The model is demonstrated on Al-insulator-Si structures containing thermally grown Ta₂O₅, previously studied in terms of microstructural, dielectric and electrical properties. The experimental results suggest that at higher current densities (>10 nA/cm²) an effect of compensation of the existing oxide charges by accumulated charges occurs. PACS 73.40.Qv; 73.50.-h; 73.61.-r; 77.55.+f     

Effects of implantation defects on the carrier concentration of 6H-SiC

The effects of ion irradiation defects on the carrier concentration of 6H-SiC epitaxial layer were studied by current–voltage (I–V), capacitance.-voltage (C–V) measurements, thermally stimulated capacitance and deep level transient spectroscopy. The defects were produced by irradiation with 10 MeV C⁺ at a fluence of 10¹¹ ions/cm² and subsequent thermal annealings were carried out in the temperature range 500–1700 K under N₂ flux. I–V and C–V measurements reveal the presence of a high defect concentration after irradiation and annealing at temperature lower than 1000 K. Thermally stimulated capacitance measurements show that some of the defects induce a deactivation of the nitrogen donor, while some of the generated defects, behaving as donor-like traps, contribute to increase the material free carrier concentration at temperatures above their freezing point. Deep level transient spectroscopy measurements performed in the temperature range 150–450 K show the presence of several overlapping traps after ion irradiation and annealing at 1000 K: these traps suffer a recovery and a transformation at higher temperatures. The annealing of all traps at temperatures as high as 1700 K allows one to completely restore the n-type conductivity. The defects mainly responsible of the observed change in the carrier concentration are identified. PACS 73.30.+y; 61.80.Jh; 61.82.Fk; 85.30.Hi     

PLD and RF-PLD synthesis of Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> ferroelectric thin films for electrically controlled devices

Ba_0.6Sr_0.4TiO₃ (BST) bulk ceramic synthesized by solid state reaction was used as target for thin films grown by pulsed laser deposition (PLD) and radiofrequency beam assisted PLD (RF-PLD). The X-ray diffraction patterns indicate that the films exhibit a polycrystalline cubic structure with a distorted unit cell. Scanning Electron Microscopy investigations showed a columnar microstructure with size of spherical grains up to 150 nm. The capacitance–voltage (C–V) characteristics of the BST films were performed by applying a DC voltage up to 5 V. A value of 280 for dielectric constant and 12.5% electrical tunability of the BST capacitor have been measured at room temperature.     

Photoluminescence of CuGaS2 and heterostructure formation with sputtered ZnS

Summary CuGaS₂ crystals grown by iodine transport exhibit room temperature photoluminescences at 2.45 eV and at 1.44 eV. The spectral distribution of the green emission is shown to be relatively well described by the calculated curve for a direct band-to-band transition withk-selection. The heterojunction formation has been tried between sulfur-treated CuGaS₂ crystals and low-resistivity amorphous ZnS films prepared by sputtering at room temperature. TheI–V characteristic of the diode shows rectifying behaviour, but no injection luminescence has been observed. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Electronic properties investigation of silicon supersaturated with tellurium

Hall measurements as a function of temperature and current–voltage (I–V) measurements have been used to study the electronic properties of silicon supersaturated with tellurium (Te). The samples were fabricated by ion implantation, followed by thermal annealing at different temperatures in N₂ and by rapid quenching. The experiment results show that the effects on the resistivity and on the Hall effect of samples implanted with high doses of Te are almost insensitive to temperature. This is not consistent with those of low dose Te implanted samples. The dark I–V characteristics and white light I–V characteristics of the junction between the high dose Te implanted layer and the substrate were also investigated. The pn junctions of samples with non equilibrium dopant concentrations exhibit decreased rectification, but increased photon to electron conversion efficiency.     

A photodiode with high rectification ratio based on well-aligned ZnO nanowire arrays and regioregular poly(3-hexylthiophene-2,5-diyl) hybrid heterojunction

A photodiode was fabricated based on well-aligned ZnO nanowire arrays (ZNAs) and regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) hybrid heterojunction. The current–voltage (I–V) characteristics of ITO/ZNAs/P3HT/Ag device in the dark and under illumination with a solar simulator were investigated in detail. The results demonstrated that the device showed good diode characteristics in the dark and under illumination. The device exhibited a high rectification ratio (RR) of 3211 at 2 V and a low turn-on voltage of 0.5 V in the dark. Also, the RR of the device as a function of illumination intensity was observed, and the transportation process of charge carriers in the diode under illumination was illuminated in terms of energy band diagram.     

Natural ageing effects of Schottky-gate GaAs FETs in current-voltage characteristics and in 1/f noise spectrum

We study the current-voltage (I–V ) characteristics and 1/f (flicker) noise spectra of experimental samples (prototypes) of submicron GaAs field-effect transistors (FETs) with Schottky planar gate in the linear regime. The model of I–V characteristics, in which the FET channel is described by the Shockley model and the crowding of current lines in passive regions is taken into account, is proposed. Analysis of the measured set of I–V characteristics allowed us to define geometric and electric parameters of the devices more precisely. The natural ageing effects were revealed by analyzing the measurements performed at a 3-year interval. We make the conjecture that excess defects are present in the structure and they are probably represented by dipoles (donor-acceptor pairs). Concentration of excess defects is estimated and its significant decrease with time is detected. For analysis of 1/f noise, we used the hypothesis of the existence of bistable point defects, assuming that the latter result in resistivity fluctuations of the conducting regions. It is shown that defects in the channel give the main contribution to 1/f noise and their concentration decreases with time. Increased content of defects near the buffer layer was detected in some devices. The experimental data obtained allow us to suppose that the observed 1/f noise is caused by the excess defects revealed in the analysis of I–V characteristics of FETs with Schottky planar gate. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 2, pp. 147–158, February 2007.     

On the current-voltage characteristic of a tunnel metal-semiconductor Schottky-Barrier contact

A possibility of a more simple and exact representation of the current-voltage (I–V) characteristic of a tunnel metal-semiconductor contact is investigated. Analysis is made on the basis of the approach proposed earlier, according to which the behaviour of the (I–V) characteristics of the Schottky-barrier contacts at low temperatures depends on the nonlinear dependence of the true (or effective for a tunnel contact) barrier height on the bias voltage. A simple equation for the (I–V) characteristic of the tunnel contact is theoretically substantiated using measurable parameters-the ideality factor n and barrier height ϕ_bm where the quantity ϕ_bn ≡ nϕ_bm plays the role of a barrier height. The calculation shows that this quantity is very close to the true barrier height of the tunnel contact (with allowance for the effect of image force) in wide current, temperature, and impurity-concentration ranges. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 18–25, March, 2006.     

Leakage current and capacitance characteristics of Si/SiO2/Si single-barrier varactor

We investigate, both experimentally and theoretically, current and capacitance (I–V/C–V) characteristics and the device performance of Si/SiO₂/Si single-barrier varactor diodes (SBVs). Two diodes were fabricated with different SiO₂ layer thicknesses using the state-of-the-art wafer bonding technique. The devices have very low leakage currents (about 5×10^-2 and 1.8×10^-2 mA/mm²) and intrinsic capacitance levels of typically 1.5 and 50 nF/mm² for diodes with 5-nm and 20-nm oxide layers, respectively. With the present device physical parameters (25-mm² device area, 760-μm modulation layer thickness and ≈10¹⁵-cm^-3 doping level), the estimated cut-off frequency is about 5×10⁷ Hz. With the physical parameters of the present existing III–V triplers, the cut-off frequency of our Si-based SBV can be as high as 0.5 THz. Received: 9 February 2001 / Accepted: 9 February 2001 / Published online: 23 March 2001     

Zero-field current-voltage characteristics in high-Tc superconductors

Zero-field current-voltage (I–V) characteristics of various high-temperature superconductor samples are analyzed in the context of the current-temperature (I−T) phase diagram. After establishing the validity and relevance of the phase diagram to these materials, the anisotropy factor is extracted from the slope ofI _c ¹ (T) (the current defined by the onset of resistance). It is concluded that studying theI−V characteristics of amples in the context of theI−T phase diagram is a simple, useful tool for comparing samples. Work supported by the Office of Naval Research.     

Barrier lowering effect and dark current characteristics in asymmetric GaAs/AlGaAs multi quantum well structure

In this study, we investigate dark current voltage characteristics of GaAs/AlGaAs staircase-like asymmetric multiquantum well structure at various temperatures experimentally. The activation energy is calculated by using Arrhenius plots at different voltages. It is found that the activation energy decreased with increasing electric field. This result is evaluated using a barrier lowering effect which is a combination of geometrical and Poole–Frenkel effects. Measured dark current density–voltage (J–V) characteristics compared with the Levine model, 3D carrier drift model and the emission capture model. The best agreement with the experimental results of dark current densities is obtained by the Levine model.