The effect of anodic oxide treatment on n-GaAs Schottky barrier diodes

The anodically treated and untreated (control sample) Au/-Cu/n-GaAs Schottky diodes have been prepared. The anodic oxidization process has been made on the n-GaAs substrate in aqueous electrolyte with pH=2.02. The anodic treatment has increased the barrier heights. We have obtained the laterally homogeneous barrier heights of approximately 0.79 and 0.91 eV for the anodically untreated and treated Au/n-GaAs SBDs, respectively, and 0.67 and 0.91 eV for the Cu/n-GaAs SBD eV respectively when accounting for the image-forge effect only. Thus, the barrier height has been increased by at least 110 and 240 meV for Au/n-GaAs and Cu/n-GaAs SBDs, respectively.     

Determination of the laterally homogeneous barrier height of metal/p-InP Schottky barrier diodes

We have reported a study of a number of metal/p-type InP (Cu, Au, Al, Sn, Pb, Ti, Zn) Schottky barrier diodes (SBDs). Each one diode has been identically prepared on p-InP under vacuum conditions with metal deposition. In Schottky diodes, the current transport occurs by thermionic emission over the Schottky barrier. The current–voltage characteristics of Schottky contacts are described by two fitting parameters such as effective barrier height and the ideality factor. Due to lateral inhomogeneities of the barrier height, both characteristic diode parameters differ from one diode to another. We have determined the lateral homogeneous barrier height of the SBDs from the linear relationship between experimental barrier heights and ideality factors that can be explained by lateral inhomogeneity of the barrier height. Furthermore, the barrier heights of metal–semiconductor contacts have been explained by the continuum of metal-induced gap states (MIGS). It has been seen that the laterally homogeneous barrier heights obtained from the experimental data of the metal/p-type InP Schottky contacts quantitatively confirm the predictions of the combination of the physical MIGS and the chemical electronegativity.     

Determination of the laterally homogeneous barrier height of metal/p-InP Schottky barrier diodes

We have reported a study of a number of metal/p-type InP (Cu, Au, Al, Sn, Pb, Ti, Zn) Schottky barrier diodes (SBDs). Each one diode has been identically prepared on p-InP under vacuum conditions with metal deposition. In Schottky diodes, the current transport occurs by thermionic emission over the Schottky barrier. The current–voltage characteristics of Schottky contacts are described by two fitting parameters such as effective barrier height and the ideality factor. Due to lateral inhomogeneities of the barrier height, both characteristic diode parameters differ from one diode to another. We have determined the lateral homogeneous barrier height of the SBDs from the linear relationship between experimental barrier heights and ideality factors that can be explained by lateral inhomogeneity of the barrier height. Furthermore, the barrier heights of metal–semiconductor contacts have been explained by the continuum of metal-induced gap states (MIGS). It has been seen that the laterally homogeneous barrier heights obtained from the experimental data of the metal/p-type InP Schottky contacts quantitatively confirm the predictions of the combination of the physical MIGS and the chemical electronegativity.     

高温Ti/4H-SiC肖特基势垒二极管的特性

在研究高温下串联电阻Ron对肖特基势垒二极管正向特性的影响，以及各种反向电流密度分量对其反向特性的影响基础上，测量并理论计算了300－528K范围内Ti/4H-SiC肖特基势垒二极管的伏安特性。分别得到了理想因子、肖特基势垒高度和串联电阻在395K和528K温度下的数值。理论和实验的比较说明，高温下，热电子发射是正向电流的主要输运机理，反向电流除了以隧道效应为主外，热电子发射电流和耗尽层中复合中心产生电流都随温度的升高而大大增加，必须加以考虑。     

Application of fluorescence microscopy for noninvasive detection of surface contamination and precursors to laser-induced damage

We present an experimental investigation to evaluate fluorescence microscopy as a tool to detect surface contamination as well as reveal surface damage precursors on optical components for large-aperture laser systems. We performed fluorescence imaging experiments using 351-nm laser excitation, whereas in situ damage testing was performed at laser fluences well below the dielectric breakdown threshold of the pure material. The experimental results demonstrated the potential of this technique to address both aforementioned technical issues.     

Schottky barrier characteristics of Pt contacts to all sputtering-made n-type GaN and MOS diodes

All sputtering-made Pt/n-GaN [metal–semiconductor (MS)] and Pt/SiO₂/n-GaN [metal–oxide–semiconductor (MOS)] diodes were investigated before and after annealing at 500 °C. n-GaN, Pt, and SiO₂ films were all fabricated by the cost-effective radio-frequency sputtering technique. A cermet target was used for depositing GaN. The Schottky barrier heights (SBHs) of both MS and MOS Schottky diodes have been investigated by the current–voltage (I–V) measurements. The results showed that SBHs increased after annealing at 500 °C for 20 min in N₂ ambient, compared to the as-deposited at 400 °C. By using Cheung’s and Norde methods, the highest SBHs of MOS Schottky diodes were respectively found to be 0.79 and 0.91 eV for the as-deposited and had reached to 0.81 and 0.94 eV after annealing. The annealed Schottky diode had showed the higher SBH, lower leakage current, smaller ideality factor, and denser microstructure.     

Barrier height enhancement in WSi x /GaAs Schottky diodes by rapid thermal annealing

The influence of rapid thermal annealing on WSi₂/GaAs and WSi_0.6/GaAs Schottky diodes was studied by means of Rutherford backscattering spectroscopy (RBS), particle induced X-ray emission spectroscopy (PIXE), X-ray diffraction (XRD) analysis and current-voltage electrical measurement. Despite the amorphicity of the layers remaining after annealing and only relatively minor changes in RBS and PIXE spectra, large barrier enhancements were registered, especially for WSi₂/GaAs diodes. For an explanation of this effect, the barrier height inhomogeneity concept is used.     

Charge accumulation on the surface of GaAs nanowires near the Schottky contact

The distribution of external potential along GaAs nanowires with electric contacts formed at the ends has been studied by the method of Kelvin probe force gradient microscopy (KPFGM). It is established that, in the case of Schottky contact formation, the application of external blocking voltage leads to charge accumulation in the surface layer of natural oxide near the contact, which significantly modifies the potential profile along the GaAs nanowire. The accumulation of charge and its dissipation upon removal of the blocking voltage proceed with characteristic times on the order of several minutes.     

Defect introduction in Ge during inductively coupled plasma etching and Schottky barrier diode fabrication processes

We have etched Sb-doped n-type (111) oriented Ge by inductively coupled plasma (ICP), using argon, and subsequently studied the defects that this process introduced as well as the effect of this etching on Schottky barrier diode quality. Deep level transient spectroscopy (DLTS) revealed that ICP etching introduced only one prominent defect, EP_0.31, in Ge with a level at 0.31 eV below the conduction band. The properties of this defect are different to those of defects introduced by other particle-related processing steps, e.g. sputter deposition and electron beam deposition, that each introduces a different set of defects. DLTS depth profiling revealed the EP_0.31 concentration was a maximum (3.6 × 10¹³ cm^− 3) close to the Ge surface and then it decreased more or less exponentially into the Ge. Annealing at 250 °C reduced the EP_0.31 concentration to below the DLTS detection limit. Finally, current-voltage (I-V) measurements as a function of temperature revealed that the quality of Schottky contacts fabricated on the ICP-etched surfaces was excellent at − 100 K the reverse leakage current at − 1 V was below 10 ¹³ A (the detection limit of our I-V instrumentation).     

Preparation and characterisation of Au/InGaP/GaAs Schottky barriers for radiation damage investigation

High quality Au/InGaP Schottky diodes have been prepared as efficient test structures for a study of the radiation hardness of InGaP as space solar cell material. A detailed characterisation of the metal–semiconductor barriers obtained on both n (free carrier concentration ranging from 3×l0¹⁵ to 1.2×l0¹⁸ cm⁻³) and p-type (3.5×10¹⁷ cm⁻³) InGaP epitaxial layers lattice matched to GaAs substrate has been performed using current–voltage, capacitance–voltage and internal photoemission techniques. Excellent electrical properties were found for low doped (ideality factor of 1.05–1.06, rectification ratio of about 10¹⁰ at 0.7 V, reverse current lower than 1×10⁻¹² A at −2 V) as well as heavily doped samples (rectification ratios of about 10⁵ at 0.6 V). The barrier height values calculated by the different techniques were compared and discussed. Deep level transient spectroscopy (DLTS) spectra obtained on unirradiated samples did not show detectable deep levels with the exception of the heaviest doped sample showing a weak peak associated to the DX centre. After electron irradiation at 9 MeV with doses ranging from 5×l0¹³ to 1.5×10¹⁵ e cm⁻² the samples exhibited a broad dominant peak (activation energy in the 0.90–0.93 eV range) whose intensity increased linearly with the absorbed dose. The broadening of the peak and the observed increase of the corresponding trap concentration with the doping level suggest that this peak could be associated to complexes due to the interaction of primary defects, created by high irradiation energy, with each others and with the shallow impurities.     

Evaluation of Schottky barrier diodes fabricated directly on processed 4H-SiC(0001) surfaces

Silicon carbide (SiC) is a suitable substrate for low-power-consumption power devices and high-temperature applications. However, this material is difficult to machine because of its hardness and chemical inertness, and many machining methods have been studied intensively in recent years. In this paper, we present a simple method to evaluate the electrical properties of the processed surface using the ideal factor n of a Schottky barrier diode (SBD) fabricated directly on the processed surface. Upon comparing the values of n for SBDs fabricated on a damaged SiC surface and a non-damaged SiC surface, we found that there is a significant difference in the dispersion and magnitude of n. Furthermore, by combining this technique with slope etching, we were able to estimate the thickness of the damaged sub-surface layer.     

Theoretical and experimental studies of Schottky diodes that use aligned arrays of single-walled carbon nanotubes

We present theoretical and experimental studies of Schottky diodes that use aligned arrays of single-walled carbon nanotubes. A simple physical model, taking into account the basic physics of current rectification, can adequately describe the single-tube and array devices. We show that for as-grown array diodes, the rectification ratio, defined by the maximum-to-minimum-current-ratio, is low due to the presence of metallic-single-walled nanotube (SWNT) shunts. These tubes can be eliminated in a single voltage sweep resulting in a high rectification array device. Further analysis also shows that the channel resistance, and not the intrinsic nanotube diode properties, limits the rectification in devices with channel length up to 10 μm.     

Calibration of surface contamination monitors for the detection of iodine incorporation in the thyroid gland

In Switzerland, individuals exposed to the risk of activity intake are required to perform regular monitoring. Monitoring consists in a screening measurement and is meant to be performed using commonly available laboratory instruments. More particularly, iodine intake is measured using a surface contamination monitor. The goal of the present paper is to report the calibration method developed for thyroid screening instruments. It consists of measuring the instrument response to a known activity located in the thyroid gland of a standard neck phantom. One issue of this procedure remains that the iodine radioisotopes have a short half-life. Therefore, the adequacy and limitations to simulate the short-lived radionuclides with so-called mock radionuclides of longer half-life were also evaluated. In light of the results, it has been decided to use only the appropriate iodine sources to perform the calibration.     

Piezoelectric-potential-controlled polarity-reversible Schottky diodes and switches of ZnO wires

Using a two-end bonded ZnO piezoelectric-fine-wire (PFW) (nanowire, microwire) on a flexible polymer substrate, the strain-induced change in I-V transport characteristic from symmetric to diode-type has been observed. This phenomenon is attributed to the asymmetric change in Schottky-barrier heights at both source and drain electrodes as caused by the strain-induced piezoelectric potential-drop along the PFW, which have been quantified using the thermionic emission-diffusion theory. A new piezotronic switch device with an "on" and "off" ratio of approximately 120 has been demonstrated. This work demonstrates a novel approach for fabricating diodes and switches that rely on a strain governed piezoelectric-semiconductor coupling process.     

Origins of the temperature dependence of the series resistance, ideality factor and barrier height based on the thermionic emission model for n-type GaN Schottky diodes

The temperature dependence of the series resistance (R_S), ideality factor (η), and barrier height (?_b) for n-type GaN Schottky diodes were studied. From the observed Hall-effect result, it is suggested that the increase of R_S with increasing temperature may result from a decrease in electron mobility with increasing temperature and the increase in the effective density of states in the conduction band with increasing temperature may lead to an increase in the energy difference between the conduction band minimum and the Fermi level and a decrease in the probability of tunneling. It is shown that the tunneling behavior is responsible for decreasing ?_b and increasing η with decreasing temperature on the basis of the thermionic emission model.     

On the examination of temperature-dependent possible current-conduction mechanisms of Au/(nanocarbon-PVP)/n-Si Schottky barrier diodes in wide range of voltage

Journal of Materials Science: Materials in Electronics - Au/(nanocarbon-PVP)/n-Si SDs were fabricated and their current-conduction mechanisms (CCMs) have been examined in elaborative by utilizing...     

Form-birefringence structure fabrication in GaAs by use of SU-8 as a dry-etching mask

A thin layer of a SU-8 submicrometer pattern produced by holographic lithography was directly used as the dry-etching mask in a chemically assisted ion-beam-etching system. With optimized etching parameters, etching selectivity of 7:1 was achieved together with a smooth vertical profile. As an application, a half-wavelength retardation plate for a 1.55-microm wavelength was produced and evaluated.     

Variable angle spectroscopic ellipsometric characterization of surface damage in chemical-mechanical polished GaAs

Variable angle spectroscopic ellipsometry (VASE) was applied to the quantitative characterization of surface and subsurface damage in GaAs, induced by conventional chemical-mechanical (CM) polishing. We show that the optimum selection of angle of incidence (75°) and spectral range (greater than or equal to 430 nm) is of crucial importance for detecting and evaluating surface and subsurface quality. The measured VASE data from 249 to 789 nm were analyzed with several fitting models. A two-layer model, with a GaAs oxide overlayer on a subsurface layer on a GaAs substrate, was found consistently to yield the best fits, suggesting the presence of subsurface damage in CM polished GaAs. In the model calculations, each composite layer was assumed, in the Bruggeman effective medium approximation, to be a simple physical mixture of the chosen constituents. The fitting results indicated that, typically, the thickness values were 2–3 nm of oxide overlayer and 15–40 nm of subsurface damage beneath it, consisting of about 1%–2% reduction in density. Independent atomic force microscopy (for surface characterization) and X-ray diffraction (for subsurface characterization) measurements were also made, for comparison with the VASE results. Consistent agreement was found.     

Analysis of surface states and series resistance in Au/n-Si Schottky diodes with insulator layer using current-voltage and admittance-voltage characteristics

In order to good interpret the experimentally observed Au/n-Si (metal-semiconductor) Schottky diodes with thin insulator layer (18 Å) parameters such as the zero-bias barrier height (Φ_bo), ideality factor (n), series resistance (R_s) and surface states have been investigated using current-voltage (I-V), capacitance-frequency (C-f) and conductance-frequency (G-f) techniques. The forward and reverse bias I-V characteristics of Au/n-Si (MS) Schottky diode were measured at room temperature. In addition, C-f and G-f characteristics were measured in the frequency range of 1 kHz-1 MHz. The higher values of C and G at low frequencies were attributed to the insulator layer and surface states. Under intermediate forward bias, the semi-logarithmic Ln (I)-V plot shows a good linear region. From this region, the slope and the intercept of this plot on the current axis allow to determine the ideality factor (n), the zero-barrier height (Φ_bo) and the saturation current (I_S) evaluated to 2.878, 0.652 and 3.61 × 10⁻⁷ A, respectively. The diode shows non-ideal I-V behavior with ideality factor greater than unity. This behavior can be attributed to the interfacial insulator layer, the surface states, series resistance and the formation barrier inhomogeneity at metal-semiconductor interface. From the C-f and G-f characteristics, the energy distribution of surface states (N_ss) and their relaxation time (τ) have been determined in the energy range of (E_c − 0.493E_v)-(E_c − 0.610) eV taking into account the forward bias I-V data. The values of N_ss and τ change from 9.35 × 10¹³ eV⁻¹ cm⁻² to 2.73 × 10¹³ eV⁻¹ cm⁻² and 1.75 × 10⁻⁵ s to 4.50 × 10⁻⁴ s, respectively.