Effect of defects on electrical properties of 4H-SiC Schottky diodes

Most of power electronic circuits use power semiconductor switching devices which ideally present infinite resistance when off, zero resistance when on, and switch instantaneously between those two states. Switches and rectifiers are key components in power electronic systems, which cover a wide range of applications, from power transmission to control electronics and power supplies.

Typical power switching devices such as diodes, thyristors, and transistors are based on a monocrystalline silicon semiconductor or silicon carbide. Silicon is less expensive, more widely used, and a more versatile processing material than silicon carbide. The silicon carbide (SiC) has properties that allow devices with high power voltage rating and high operating temperatures. The technology overcomes some crystal growth obstacles, by using the hydrogen in the fabrication of 4H-SiC wafers.

The presence of structural defects on 4H-SiC wafers was shown by different techniques such as optical microscopy and scanning electron microscopy. The presence of different SiC polytypes inclusions was found by Raman spectroscopy. Schottky diodes were realized on investigated wafers in order to obtain information about the correlation between those defects and electrical properties of the devices. The diodes with voltage breakdown as 600 V and ideality factor as 1.05 were obtained and characterized after packaging.     

Electrical transport characteristics of Au/n-GaN Schottky diodes

The current–voltage measurements were performed in the temperature range (80–300 K) on Au/ n-GaN Schottky barrier type diodes. The Schottky diode shows non-ideal I(V_G) behaviour with ideality factors n equals to 1.18 and 1.81 at 300 K and 80 K, respectively, and are thought to have a metal-interface layer-semiconductor configuration. Under forward bias and for T ≥ 200 K, the electrical current transport was controlled by the thermionic emission (TE) process. However, for T ≤ 200 K, The current was controlled by the thermionic field emission (TFE). The characteristic energy E₀₀ = 3.48 meV was obtained from the I(V_G, T) measurements and agreed very well with the value of E₀₀ = 3.62 meV calculated theoretically. The zero-bias barrier height ϕ_B0 determined from the I(V_G) measurements was 0.84 eV at 300 K and decreases to 0.49 eV at 80 K.     

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。     

Capacitance-voltage measurements on Schottky diodes with poor ohmiccontacts

The frequency-dependent admittance of Al-GaAs Schottky diodes with nonideal ohmic contacts is tested, using a simple three-component small-signal equivalent circuit model. Both the ohmic and the rectifying contacts of this diode are produced during one process step. This simplifies the formation procedure and saves testing time and costs. However, the nonalloyed ohmic contacts lead to a high series resistance, minority carrier injection, and deep level influence. All of these effects give a frequency-dependent diode admittance. Frequency-dependent admittance analysis in a certain frequency range using the three-component equivalent circuit model leads to the space-charge capacitance of the diode reflecting only the free majority carriers. The method is highly suitable for the automatic routine control of semiconductor material properties, diode, or gate capacitances     

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.     

Requirements imposed on the electrical properties of the absorber layer in CdTe-based solar cells

The requirements for minimizing the electric losses in the CdTe layer in CdS/CdTe thin-film solar cells are discussed. It is shown that for achieving the total absorption of the radiation and to avoid electrical losses, the separation between Fermi level and the valance band should not be more than 0.3 eV. In order to fix the Fermi level near the valence band, it is necessary to dope with acceptor impurities which can introduce shallow level in the band gap with a concentration considerably exceeding the concentration of native impurities and defects (10¹⁵–10¹⁶ cm⁻³). Taking into account the fact that the location of the Fermi level in the bandgap of a semiconductor depends on the degree of compensation, the energy of ionization of the impurity should not be greater than 0.05–0.15 eV.

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Electrical properties of Schottky diodes based on Carbazole

Sandwich structures of Carbazole thin films have been prepared by using vacuum deposition technique. The plot of current density versus voltage (J–V characteristics) shows two distinct regions. In the lower voltage region ohmic conduction and in the higher voltage region space charge limited conduction (SCLC) is observed. Number of states in the valence band (Nv) is calculated from the temperature dependence of J in the ohmic region. From the temperature dependence of J in the SCLC region trap density (Nt) and activation energy are determined. The values of Nv and Nt are in the order 10²³ m⁻³ and 10²⁷ m⁻³ respectively. The value of activation energy is nearly equal to 0.1 eV and that of the effective mobility is 4.5 × 10⁻⁷ cm² V⁻¹ S⁻¹. Schottky diodes are fabricated using Aluminium (Al) as Schottky contact. It is observed that gold (Au) is more suitable for ohmic contact compared to silver (Ag). From a semi logarithmic plot of J versus V, the barrier height (ϕb), diode ideality factor (n) and saturation current density (J₀) are determined. The value of n increases and ϕb decreases on annealing.     

Electrical properties of Schottky diodes using high-resistivity CdTe crystals

The Schottky barrier height is measured for single crystals doped with the halogens Cl, Br, and I during growth by chemical transport reactions. The measurements are made using a modification of the F(V) function [N. V. Agrinskaya, Mater. Sci. Eng. B 16, 172 (1993)] proposed by the authors. Pis’ma Zh. Tekh. Fiz. 25, 23–28 (August 26, 1999)     

Characteristics of gold/cadmium sulfide nanowire Schottky diodes

Schottky diode junctions were formed between nanowires of cadmium sulfide and nanowires of gold, through sequential cathodic electrodeposition into the pores of anodized aluminum oxide (AAO) templates. Lengths of CdS and Au nanowires were 100-500 nm and 300-400 nm respectively, while the diameter was 30 nm, each. Analysis of Schottky diodes yielded an effective reverse saturation current (J_o), of 0.32 mA/cm² and an effective diode ideality factor (A) of 8.1 in the dark. Corresponding values under one sun illumination were, J_o = 0.92 mA/cm² and A = 10.0. Dominant junction current mechanisms are thought to be tunneling and/or interface state recombination.     

Radiation damage of SiC Schottky diodes by electron irradiation

The impact of radiation damage on the device performance of 4H-SiC Schottky diodes, which are irradiated at room temperature with 2-MeV electrons is studied. After irradiation the reverse current increases, while the forward current and the capacitance decrease with barrier height and carrier density. The decrease of the barrier height is mainly responsible for the increase of the reverse current, while the decrease of the forward current for a high fluence is caused by the increase of the resistance in the bulk of the crystal. Although no electron capture levels are observed before irradiation, three electron capture levels (E₁, E₂, and E₃) are induced after irradiation. It is noted that the decrease in carrier density is partly caused by the contribution of non-observed electron capture level in the DLT spectrum, which compensates the free carriers.     

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.     

Characteristics of Pd/InGaP Schottky diodes hydrogen sensors

Pd/InGaP hydrogen sensors based on the metal-oxide-semiconductor (MOS) and metal-semiconductor Schottky diodes have been fabricated and systematically studied. The effects of hydrogen adsorption on device performances such as the current-voltage characteristics, barrier height variation, hydrogen coverage, and heat of adsorption are investigated. The studied devices exhibit very wide hydrogen concentration detection regimes and remarkable hydrogen-sensing properties. Particularly, an extremely low hydrogen concentration of 15 ppm H/sub 2//air at room temperature can be detected. In addition, under the presence of oxide layers in the studied MOS device structure, the enhancements of barrier height and high-temperature operating capability are observed. The initial heat of adsorption for Pd/oxide and Pd/semiconductor interface are calculated as 355 and 65.9 meV/atom, respectively. Furthermore, the considerably short response times are found in studied devices.     

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.     

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.     

Infrared response of epitaxial and polycrystalline CoSi2 Schottky diodes

Abstract

The influence of grain boundary scattering of excited carriers in CoSi₂/Si Schottky diodes has been investigated by measuring the infrared response of epitaxial and polycrystalline silicide films on Si(100). An improvement in the quantum efficiency of polycrystalline diodes has been observed for thick silicide films, indicating that carriers are scattered at the grain boundaries of the silicide. The polycrystalline diodes show a quantum efficiency twice that of epitaxial detectors. The Schottky barrier height has been measured by different methods, and a difference of only a few meV is observed between the polycrystalline and the epitaxial diodes.     

Terahertz Schottky barrier diodes with various isolation designs for advanced radio frequency applications

High performance nanometer NiSi2-Si Schottky barrier diode arrays (SBDA) with various isolation designs, including poly Si gate (PSG) and resist protection oxide (RPO), are developed for advanced radio frequency applications. Radio frequency performances of these developed SBDAs are investigated and compared to that with the conventional shallow trench isolation. All of the SBDAs are fabricated with a foundry state-of-the -art 45 nm complementary metal oxide semiconductor technology. Both of PSG and RPO insulated SBDAs have higher cutoff frequency and a simpler preparation process. Specifically, the PSG insulted SBDA could achieve a cutoff frequency of up to 4.6 THz.     

Theory of fluidized-bed electrical conduction

Mechanisms for the passage of electric current through a fluidized bed are discussed, and corresponding estimates for the effective electrical conductivity are given.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 11, pp. 889–900, November, 1978.     

Structural,optical, and electrical properties of Schottky diodes based on undoped and cobalt-doped ZnO nanorods prepared by RF-magnetron sputtering

Cobalt-doped ZnO nanorods were successfully synthesized on Si/SiO₂ substrate using RF-magnetron sputtering at room temperature. The undoped and Co-doped ZnO nanostructures were characterized by XRD, FE-SEM, AFM, and PL spectra. The results showed that Co²⁺ replaced Zn²⁺ in the ZnO lattice without changing the wurtzite structure. The ZnO structure became high crystallite and was gradually converted into nanorods without extra phases as increased cobalt doping levels to 3 at.% and 4 at.%. The as-synthesized nanorod arrays were dense and vertically grew on the substrate with lengths of approximately 341 and 382.3 nm for 3 at.% and 4 at.% CO, respectively. PL analysis revealed that the ultraviolet (UV) emission intensity decreased and exhibited a blue shift with increased Co atomic percentage. This result was consistent with the energy bandgap values (3.26–3.3 eV) obtained from UV–vis spectra. The I–V characteristics revealed that the Shottky diodes based on Co-doped ZnO nanostructure with Pd electrodes have high barrier height (0.715–0.797 eV) and low saturation current (0.035–0.841 μA). The barrier height decreased after annealing the diodes at 500 °C for 2 h. To the best of our knowledge, Schottky diodes based on Co-doped ZnO nanorods prepared by RF-magnetron sputtering have not yet been reported.     

Dopant concentration dependence of the response of SiC Schottky diodes to light ions

The responses of Silicon Carbide (SiC) Schottky diodes of different dopant concentration to ¹²C ions at 14.2, 28.1 and 37.6 MeV incident energies are compared. The relation between the applied reverse bias and the thickness of the depleted epitaxial region is studied for different dopant concentrations. The experimental data show that SiC diodes with lower dopant concentration need lower reverse bias to be depleted. Moreover it has been observed that the energy resolution, measured as a function of the applied reverse bias and of the ions incident energies, does not depend on the dopant concentration. The radiation damage, produced by irradiating SiC diodes of different dopant concentration with ¹⁶O ions at 35.2 MeV, was evaluated by measuring the degradation of both the signal pulse-height and the energy resolution as a function of the ¹⁶O fluence. Diodes having a factor 20 lower dopant concentration exhibit a radiation hardness reduced by 60%. No inversion in the signal at the breakdown fluence was observed for ¹⁶O ions stopped inside the diode epitaxial region.