Electrical Characteristics of Co/n-Si Schottky Barrier Diodes Using I-V and C-V Measurements

Electrical characteristics of Co/n-Si Schottky barrier diodes are analysed by current- voltage （I- V） and capacitancevoltage （C- V） techniques at room temperature. The electronic parameters such as ideality factor, barrier height and average series resistance are determined. The barrier height 0. 76 eV obtained from the C - V measurements is higher than that of the value 0. 70 eV obtained from the I - V measurements. The series resistance Rs and the ideality factor n are determined from the d ln（ I） /dV plot and are found to be 193.62 Ω and 1.34, respectively. The barrier height and the Rs value are calculated from the H（I） - I plot and are found to be 0.71 eV and 205.95Ω. Furthermore, the energy distribution of the interface state density is determined from the forward bias I - V characteristics by taking into account the bias dependence of the effective barrier height. The interface state density Nss ranges from 6.484×10^11 cm^-2eV^-1 in （Ec - 0.446） eV to 2.801×10^10 cm^-2eV^-1 in （Ec - 0.631） eV, of the Co/n-Si Schottky barrier diode. The results show the presence of a thin interracial layer between the metal and the semiconductor.     

Temperature-dependent optical absorption measurements and Schottky contact behavior in layered semiconductor n-type InSe(:Sn)

The layered n-InSe(:Sn) single crystal samples have been cleaved from a large crystal ingot grown from non-stoichiometric melt by the Bridgman-Stockbarger method. It has been made the absorption measurements of these samples without Schottky contact under electric fields of 0.0 and 6000 V cm⁻¹. The band gap energy value of the InSe:Sn has been calculated as 1.36 ± 0.01 eV (at 10 K) and 1.28 ± 0.01 eV (at 300 K) under zero electrical field, and 1.31 ± 0.01 eV (at 10 K) and 1.26 ± 0.01 eV (at 300 K) under 6000 Vcm⁻¹. The current-voltage (I-V) characteristics of Au-Ge/InSe(:Sn)/In Schottky diodes have been measured in the temperature range 80-320 K with a temperature step of 20 K. An experimental barrier height (BH) Φ_ap value of about 0.70 ± 0.01 eV was obtained for the Au-Ge/InSe(:Sn)/In Schottky diode at the room temperature (300 K). An abnormal decrease in the experimental BH Φ_b and an increase in the ideality factor n with a decrease in temperature have been explained by the barrier inhomogeneities at the metal-semiconductor interface. From the temperature-dependent I-V characteristics of the Au-Ge/InSe(:Sn)/In contact, that is, and A^* as 0.94 ± 0.02 and 0.58 ± 0.02 eV, and 27 ± 2 and 21 ± 1 (A/cm² K²), respectively, have been calculated from a modified versus 1/T plot for the two temperature regions. The Richardson constant values are about two times larger than the known value of 14.4 (A/cm² K²) known for n-type InSe. Moreover, in the temperature range 80-320 K, we have also discussed whether or not the current through the junction has been connected with TFE.     

The conductance and capacitance-frequency characteristics of Au/pyronine-B/p-type Si/Al contacts

The rectifying junction characteristics of the organic compound pyronine-B (PYR-B) film on a p-type Si substrate have been studied. The PYR-B has been evaporated onto the top of p-Si surface. The barrier height and ideality factor values of 0.67 ± 0.02 eV and 2.02 ± 0.03 for this structure have been obtained from the forward bias current-voltage (I-V) characteristics. The energy distribution of the interface states and their relaxation time have been determined from the forward bias capacitance-frequency and conductance-frequency characteristics in the energy range of ((0.42 ± 0.02) − E_v)-((0.66 ± 0.02) − E_v) eV. The interface state density values ranges from (4.21 ± 0.14) × 10¹³ to (3.82 ± 0.24) × 10¹³ cm⁻² eV⁻¹. Furthermore, the relaxation time ranges from (1.65 ± 0.23) × 10⁻⁵ to (8.12 ± 0.21) × 10⁻⁴ s and shows an exponential rise with bias from the top of the valance band towards the midgap.     

Temperature dependence of the current-voltage characteristics of the Al/Rhodamine-101/p-Si(1 0 0) contacts

The current-voltage (I-V) characteristics of Al/Rhodamine-101/p-Si/Al contacts have been measured at temperatures ranging from 280 to 400 K at 20 K intervals. A barrier height (BH) value of 0.817 eV for the Al/Rh101/p-Si/Al contact was obtained at the room temperature that is significantly larger than the value of 0.58 eV of the conventional Al/p-Si Schottky diode. While the barrier height Φ_b0 decreases the ideality factors (n) become larger with lowering temperature. The high values of n depending on the sample temperature may be ascribed to decrease of the exponentially increase rate in current due to space-charge injection into Rh101 thin film at higher voltage. Therefore, at all temperatures, it has been seen that the I-V characteristics show three different regions, the ohmic behavior at low voltages, and the space charge limited current with an exponential distribution of traps at high voltages.     

Electronic Transport Properties of （7,0） Semiconducting Carbon Nanotube

Electronic transport properties of a finite （7,0） carbon nanotube （CNT） coupled to Au （111） surfaces are investigated with a fully nonequilibrium Green＇s functions method combined with the density functional theory. The results show that the coupling effect between the CNT and Au electrode plays an important role in the transport properties, which leads to the formation of a high plateau in the transmission spectrum around Fermi energy. In addition, the current-voltage characteristic of the （7,0） CNT coupled to Au electrodes is different from an isolated （7,0） CNT.     

An anchoring strategy for photoswitchable biosensor technology: azobenzene-modified SAMs on Si(111)

A mild and efficient procedure has been developed to obtain covalently attached self-assembled monolayers (SAMs) on Si(111) with photochromic azobenzene head-groups. Starting from neat or diluted carboxylic acid functionalized monolayers on-chip coupling reactions were applied to attach hydroxyl-functionalized azobenzene units to the SAMs by ester bond formation. The modified surfaces were characterized by high-resolution X-ray photoelectron spectroscopy (XPS), transmission Fourier transform infrared spectroscopy (FT-IR), and contact angle measurements. Reversible cis ↔ trans isomerizations of photoswitchable SAMs were monitored by wettability measurements. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users. Dedicated with respect and compliments to Professor Helmut Schwarz on the occasion of his 65th birthday.     

Current-voltage characteristics of Au/GaN/GaAs structure

Au/GaN/n-GaAs structure has been fabricated by the electrochemically anodic nitridation method for providing an evidence of achievement of stable electronic passivation of n-doped GaAs surface. The change of the electronic properties of the GaAs surface induced by the nitridation process has been studied by means of current-voltage (I-V) characterizations on Schottky barrier diodes (SBDs) shaped on gallium nitride/gallium arsenide structure. Au/GaN/n-GaAs Schottky diode that showed rectifying behavior with an ideality factor value of 2.06 and barrier height value of 0.73 eV obeys a metal-interfacial layer-semiconductor (MIS) configuration rather than an ideal Schottky diode due to the existence of GaN at the Au/GaAs interfacial layer. The formation of the GaN interfacial layer for the stable passivation of gallium arsenide surface is investigated through calculation of the interface state density N_ss with and without taking into account the series resistance R_s. While the interface state density calculated without taking into account R_s has increased exponentially with bias from 2.2×10¹² cm⁻² eV⁻¹ in (E_c−0.48) eV to 3.85×10¹² cm⁻² eV⁻¹ in (E_c−0.32) eV of n-GaAs, the N_ss obtained taking into account the series resistance has remained constant with a value of 2.2×10¹² cm⁻² eV⁻¹ in the same interval. This has been attributed to the passivation of the n-doped GaAs surface with the formation of the GaN interfacial layer.     

Spectroscopy and imaging of metal-organic interfaces using BEEM

Charge injection from metal electrodes to organics is a subject of intense scientific investigation for organic electronics. Ballistic electron emission microscopy (BEEM) enables spectroscopy and imaging of buried interfaces with nanometer resolution. Spatial non-uniformity of carrier injection is observed for both Ag-PPP (poly-paraphenylene) and Ag-MEHPPV (poly-2-methoxy-5-2-ethyl-hexyloxy-1,4-phenylenevinylene) interfaces. BEEM current images are found to correlate only marginally with the surface topography of the Ag film.     

III–V semiconductor interface properties as a knowledge basis for modern heterostructure devices

Some examples of interface studies are reported which show their close link with progress in III–V modern semiconductor device physics and technology. The surface electronic properties investigated in-situ by reflectance anisotropy spectroscopy during InGaP/InP growth (metal-organic vapor-phase epitaxy) are essential for the control of ordering phenomena in these layers, which is relevant for high-performance optoelectronic devices. Studies of electronic interface states at metal/narrow-gap III–V semiconductors are presented, which enabled the successful preparation of semiconductor/superconductor hybrid devices. For group-III nitrides with wurtzite structure the presence of fixed polarization interface charges yields new challenges in order to understand and control Schottky-barrier heights, band offsets and 2D confinement in heterostructure field-effect transistors. Received: 26 April 2001 / Accepted: 23 July 2001 / Published online: 3 April 2002     

Optical properties of epitaxial CuGaS2 layers on Si(111)

CuGaS₂ films epitaxially grown on Si(111) substrates by molecular beam epitaxy from elemental sources were investigated by various optical methods. Photoluminescence studies at low temperatures reveal a strong dependence of the near-bandgap emission on the composition. Ga-rich films show predominantly donor–acceptor pair recombination, while additionally free-to-bound and excitonic transitions are found for stoichiometric and Cu-rich films. Low lineshape broadening of the free excitonic transitions FX^A and FX^B/C in the photoreflectance spectra up to room temperature demonstrates the high crystal quality. The assignment of these transitions is confirmed by polarisation dependent photocurrent measurements making use of the optical selection rules and the three different growth directions for the c-axis of CuGaS₂ relative to the Si-substrate. A fit to the photocurrent measurements yields the relative volume fraction of each c-axis orientation.     

Temperature-Dependent Transport Properties in Oxide p-n Junction above Room Temperature

Oxide p-n junctions ofp-SrIn_0.1Ti_0.9O₃/n-SrNb_0.01Ti_0.99O₃ (SITO/SNTO) are fabricated by laser molecular beam epitaxy. The current-voltage characteristics of the SITO/SNTO p-n junction are investigated mainly in the temperature range of 300--400K. The SITO/SNTO junction exhibited good rectifying behaviour over the wholetemperature range. Our results indicate a possibility of application of oxide p-n junction in higher temperatures in future electronic devices.     

Numerical analysis of gate leakage current in AlGaN Schottky diodes

We studied theoretically the influence of the tunneling current on the leakage current in AlGaN Schottky diodes. It is shown that the most important conductance mechanism in these structures is the tunneling. The thermionic emission has lower influence on the total current practically throughout the whole reverse bias range and doping concentrations studied. For high doping concentrations we found very slow temperature dependence of the diode current.     

Investigation of electrical and ammonia sensing characteristics of Schottky barrier diode based on a single ultra-long ZnO nanorod

Novel ultra-long ZnO nanorods, with lengths about 0.5-1.5 mm and diameters ranging from 100 to 1000 nm, in mass production have been synthesized via the vapor-phase transport method with CuO catalyst at 900 °C. Rectifying Schottky barrier diodes have been fabricated by aligning a single ultra-long ZnO nanorod across paired Ag electrodes. The resulting current-voltage (I-V) characteristics of the SBD exhibit a clear rectifying behavior. The ideality factor of the diode is about 4.6, and the threshold voltage is about 0.54 V at room temperature (300 K). At the same time the detailed I-V characteristics have been investigated in the temperature range 423-523 K. In addition, after exposure of the Schottky diodes to NH₃, the forward and reverse currents increase rapidly, indicating a high sensitivity to NH₃ gas.     

Passivation of Si (111) surfaces by ordered metal layers

The properties of √3 × √3 ordered gold and silver monolayers on a Si(111) substrate have been investigated by Auger, low energy electron diffraction and photo-emission analysis. It has been found that oxygen adsorption on these surfaces is considerably weaker than on clean Si surfaces. This new result clearly emphasizes the correlation between the oxidation properties of Si atoms and their local environment. A comparison is made with previous results concerning Au-Si amorphous metallic alloys where gold atoms act as a catalyst for the oxidation.     

Current transport in Pd2Si/n-Si(100) Schottky barrier diodes at low temperatures

The forward current-voltage (I–V) characteristics of Pd₂Si/n-Si(100) Schottky barrier diodes are shown to follow the Thermionic Emission-Diffusion (TED) mechanism in the temperature range of 52-295 K. The evaluation of the experimentalI–V data reveals a decrease of the zero-bias barrier height ( _b0) and an increase of the ideality factor () with decreasing temperature. Further, the changes in _b0 and become quite significant below 148 K. It is demonstrated that the findings cannot be explained on the basis of tunneling, generation-recombination and/or image force lowering. Also, the concepts of flat band barrier height and T ₀-effect fail to account for the temperature dependence of the barrier parameters. The 1n(I _s /T ²) vs 1/T plot exhibits nonlinearity below 185 K with the linear portion corresponding to an activat ion energy of 0.64 eV, a value smaller than the zero-bias barrier height energy (0.735 eV) of Pd₂Si/n-Si Schottky diodes. Similarly, the value of the effective Richardson constant A** turns out to be 1.17 × 10⁴ A m^–2 K^–2 against the theoretical value of 1.12 × 10⁶ A m^–2 K^–2. Finally, it is demonstrated that the observed trends result due to barrier height inhomogeneities prevailing at the interface which, in turn, cause extra current such that theI–V characteristics continue to remain consistent with the TED process even at low temperatures. The inhomogeneities are believed to have a Gaussian distribution with a mean barrier height of 0.80 V and a standard deviation of 0.05 V at zero-bias. Also, the effect of bias is shown to homogenize barrier heights at a slightly higher mean value.     

Poly-benzyl domains grown on porous silicon and their I-V rectification

Microwave-irradiated polymerization of benzyl chloride and triphenyl chloromethane on hydride-terminated porous silicon (PS) was achieved through the use of Zn powder as a catalyst. Transmission infrared Fourier-transform spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses confirmed the poly-benzyl membranes grafted on PS. Topographical images by AFM revealed crystal-like domains rather than homogenous monolayers on the surface. The current-voltage measurements in nano-scale by current sensing atomic force microscopy (CS-AFM) showed the rectification behavior of this polymer membrane. Finally, mechanism of a radical initiation on the surface and a following Friedel-Crafts alkylation was proposed for the covalent assembly of poly-benzyl domains.     

Characteristics of low-temperature-grown GaN films on Si(111)

In this paper, we report on the characteristics of GaN films grown on Si(111) at a low temperature (200 °C) by electron cyclotron resonance (ECR) plasma-assisted metalorganic chemical vapor deposition (PA-MOCVD). Structural analysis of the GaN films was performed by using scanning electron microscopy (SEM), atomic force miscroscopy (AFM), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), and Rutherford backscattering spectrometry (RBS). Post deposition analysis revealed high quality crystalline GaN was obtained at this low temperature. Electrical analysis of the GaN films was done by using current-voltage (I-V) measurements where electrical characterizations were carried on GaN/Si heterojunction and Schottky barrier diodes. Rectification behaviour was observed for the isotype GaN/Si (n-n) heterojunction. Ideality factors and Schottky barrier heights for Ni and Cr Schottky barriers on GaN, were deduced to be 1.4 and 1.7; and 0.62 and 0.64 eV, respectively.     

Debye's relaxation frequency: A poor man's approach

We present a simple approach to introduce Debye's relaxation frequency. Our model is based on a kinetic equation at the electrodes, describing the time variation of the ionic charge pushed at the limiting surfaces by the effective electric field. In a first approximation the surface region where the ions are confined is assumed of negligible thickness. We show that this approximation allows to define a frequency at which the effective resistance of the sample begins to decrease. This frequency coincides with Debye's relaxation frequency. An equivalent electric circuit describing the frequency dependence of the effective impedance of the cell, valid in this approximation, is presented. In a second approximation we discuss the influence of a perfectly dielectric surface layer on the relaxation frequency, where the electrolytic cell is described by means of a Maxwell-Wagner system. The equivalent electrical circuit is discussed.     

Reproducible resistive switching effect for memory applications in heterocontacts based on strongly correlated electron systems

The transitional processes in heterocontacts based on strongly correlated electron systems (SCES) are studied for analyzing of the effect of resistive switching (ERS). It has been shown that the process is asymmetric with respect to switching into “on” and “off” states, the switching time is controlled by a voltage level, this time can be less than microseconds, on the other hand, relaxation processes can reach tens seconds. The switching is controlled by two processes: a change in the resistance state of the normal metal/SCES interface under effect of electric current field and by electrodiffusion of oxygen to vacancies, at that the doping level of the contact area and resistive properties of the heterocontact change. In particular, electrodiffusion of mobile oxygen induced by the electric field makes it possible to use a device with ERS as a memristor. On the other hand, a possibility to control the switching time and ON and OFF parameters show the possibilities to use these devices as memory elements “RAM”.     

From semiclassical transport to quantum Hall effect under low-field Landau quantization

The crossover from the semiclassical transport to the quantum Hall effect is studied by examining a two-dimensional electron system in an AlGaAs/GaAs heterostructure. By probing the magneto-oscillations, it is shown that the semiclassical Shubnikov-de Haas (SdH) formulation can be valid even when the minima of the longitudinal resistivity approach zero. The extension of the applicable range of the SdH theory could be due to the damping effects resulting from disorder and temperature. Moreover, we observed plateau-plateau transition-like behavior with such an extension. From our study, it is important to include positive magnetoresistance to refine the SdH theory.