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 and optical properties of poly(2-dodecanoylsulfanyl-<Emphasis Type="Italic">p</Emphasis>-phenylenevnylene) and its application in electroluminescent devices

We describe the optical and electrical characterization of a poly(p-phenylenevinylene) derivative: poly(2-dodecanoylsulfanyl-p-phenylenevinylene) (12COS-PPV). The electrical characterization was carried out on devices with the FTO\PEDOT:PSS\12COS-PPV/Al structure. Positive charge carrier mobility μ _h of ~1.0 × 10⁻⁶ cm² V⁻¹ s⁻¹ and barrier height φ of ~0.1 eV for positive charge carrier injection at the PEDOT:PSS/12COS-PPV interface were obtained using a thermionic injection model. FTO\PEDOT:PSS\12COS-PPV/Ca devices exhibited green-yellow electroluminescence with maximum emission at λ = 540 nm.     

Electrical and structural properties of double metal structure Ni/V Schottky contacts on n-InP after rapid thermal process

The electrical, structural, and surface morphological properties of Ni/V Schottky contacts have been investigated as a function of annealing. The Schottky barrier height value from I–V and C–V measurements for as-deposited Ni/V/n-InP diode is 0.61 eV (I–V) and 0.91 eV (C–V), respectively. It has been observed that the Schottky barrier height decreases with increasing annealing temperature as compared to the as-deposited contact. For the contact annealed at 200 °C, the obtained barrier height decreased to 0.52 eV (I–V) and 0.78 eV (C–V). Further, the annealing temperature increased to 300 and 400 °C, the barrier height slightly increased to 0.58 eV (I–V), 0.82 eV (C–V) and 0.59 eV (I–V), 0.88 eV (C–V). However, after annealing at 500 °C, results then decrease in barrier height to 0.51 eV (I–V) and 0.76 eV (C–V), which is lower than the value obtained for the sample annealed at 200 °C. The Norde method is also employed to extract the barrier height of Ni/V/InP Schottky diode, and the values are 0.68 eV for the as-deposited and 0.56 eV for the contact annealed at 500 °C, which are in good agreement with those obtained by I–V technique. Based on the results of AES and XRD studies, it is concluded that the formation of indium phases at the Ni/V/n-InP interface may be the reason for the increase in the barrier height for the as-deposited contact. The decrease in the barrier height upon annealing at 500 °C may be due to the formation of phosphide phases at the interface. The AFM results showed that there is no significant degradation in the surface morphology (RMS roughness of 0.61 nm) of the contact even after annealing at 500 °C.     

Physical Properties of AZ91D Measured Using the Draining Crucible Method: Effect of SF<Subscript>6</Subscript>

The draining crucible (DC) technique was used for measurements on AZ91D under Ar and SF₆. The DC technique is a new method developed to simultaneously measure the physical properties of fluids, the density, surface tension, and viscosity. Based on the relationship between the height of a metal in a crucible and the outgoing flow rate, a multi-variable regression is used to calculate the values of these fluid properties. Experiments performed with AZ91D at temperatures from 923 K to 1173 K indicate that under argon, the surface tension (N · m⁻¹) and density (kg · m⁻³) are [0.63 − 2.13 × 10⁻⁴ (T − T _L)] and [1656 − 0.158 (T − T _L)], respectively. The viscosity (Pa · s) has been determined to be [1.455 × 10⁻³ − 1.209 × 10⁻⁵ (T − T _L)] over the temperature range from 921 K to 967 K superheat. Above 967 K, the viscosity of the alloy under argon seems to be constant at (2.66 × 10⁻⁴ ± 8.67 × 10⁻⁵) Pa · s. SF₆ reduces the surface tension of AZ91D.     

Features of current flow in structures based on Au/Ti/n-InAlAs Schottky barriers

Current–voltage (I–V) characteristics of Au/Ti/n-InAlAs/InP Shottky barriers have been studied in a temperature range of 100–380 K. It is established that, as the temperature increases from 100 to 200 K, the ideality factor drops from 1.58 to 1.1, while the barrier height grows from 0.55 to 0.69 eV. With a subsequent temperature increase from 200 to 380 K, both the ideality factor and barrier height vary, but only weakly. This behavior agrees well with the model of lateral inhomogeneity of the barrier height (Tung model), which is confirmed by the linear dependence of the barrier height on the ideality factor at temperatures within 100–200 K. Calculations according to this model yielded the value of 0.88 eV for the homogeneous-junction barrier height, 10^–4 cm^2/3 V^1/3 for the mean-square deviation of the Gaussian distribution of barrier heights, 3.7 × 10^–11 cm² for the effective area of regions with reduced barrier heights, and 10.7 A cm^–2 K^–2 for the Richardson constant.

     

Thermal and Doping Effect on Sn/(n)ZnO Schottky Junction and Its Performance as a <Emphasis Type="Italic">PV</Emphasis> Effect

Thin film Sn/(n)ZnO Schottky junctions with different doping concentrations were prepared by vacuum evaporation. Different junction parameters such as ideality factor, barrier height, Richardson’s constant, short-circuit current, etc. were determined from I–V characteristics. These parameters were found to change significantly with variations of doping concentration and temperature. The structures showed the change of the PV effect, giving a fill factor of 0.42 (efficiency of 0.39 %) with an open-circuit voltage of 124mV and a short-circuit current density of 113 × 10⁻⁵ A ·cm⁻² for a doping concentration, N _d = 3.88 × 10¹⁵ cm ⁻³(2.74 % Al-doped ZnO). However, by increasing the doping concentration, the efficiency was found to increase by up to 4.54 % for doping concentration, N _d = 2.28 × 10¹⁷ cm ⁻³. The conversion efficiencies varied with temperature and were observed to have an overall improvement up to 343 K. Proper doping, annealing, and hydrogenation are necessary to reduce the series resistance so as to achieve an ideal and high efficiency PVconverter.     

Barrier characteristics of Pt/Ru Schottky contacts on <Emphasis Type="Italic">n</Emphasis>-type GaN based on <Emphasis Type="Italic">I–V–T</Emphasis> and <Emphasis Type="Italic">C–V–T</Emphasis> measurements

We have investigated the current–voltage (I–V) and capacitance–voltage (C–V) characteristics of Ru/Pt/n-GaN Schottky diodes in the temperature range 100–420 K. The calculated values of barrier height and ideality factor for the Ru/Pt/n-GaN Schottky diode are 0·73 eV and 1·4 at 420 K, 0·18 eV and 4·2 at 100 K, respectively. The zero-bias barrier height (Φ_b0) calculated from I–V characteristics is found to be increased and the ideality factor (n) decreased with increasing temperature. Such a behaviour of Φ_b0 and n is attributed to Schottky barrier (SB) inhomogeneities by assuming a Gaussian distribution (GD) of barrier heights (BHs) at the metal/semiconductor interface. The current–voltage–temperature (I–V–T) characteristics of the Ru/Pt/n-GaN Schottky diode have shown a double Gaussian distribution having mean barrier heights ( [`(F)]<sub>\textb0</sub> {\bar{{\Phi}}_{\text{b}0}} ) of 1·001 eV and 0·4701 eV and standard deviations (σ <sub>0</sub>) of 0·1491 V and 0·0708 V, respectively. The modified ln (J<sub>0</sub> /T<sup>2</sup> )-( q<sup>2</sup>s <sub>0</sub><sup>2</sup>/2k<sup>2</sup>T<sup>2</sup> ){ln} ({{J}_{0} /{T}^{2}} )-( {{q}^{2}{\sigma} _{0}^{2}/{2}{k}^{2}{T}^{2}} ) vs 10<sup>3</sup>/T plot gives [`(F)]_\textb0 \bar{{\Phi}}_{\text{b}0} and Richardson constant values as 0·99 eV and 0·47 eV, and 27·83 and 10·29 A/cm²K², respectively without using the temperature coefficient of the barrier height. The difference between the apparent barrier heights (BHs) evaluated from the I–V and C–V methods has been attributed to the existence of Schottky barrier height inhomogeneities.     

Structural and electrical properties of swift heavy ion beam irradiated Fe/Si interface

The present work deals with the mixing of iron and silicon by swift heavy ions in high-energy range. The thin film was deposited on a n-Si (111) substrate at 10⁻⁶ torr and at room temperature. Irradiations were undertaken at room temperature using 120 MeV Au⁺⁹ ions at the Fe/Si interface to investigate ion beam mixing at various doses: 5 × 10¹² and 5 × 10¹³ ions/cm². Formation of different phases of iron silicide has been investigated by X-ray diffraction (XRD) technique, which shows enhancement of intermixing and silicide formation as a result of irradiation. I-V measurements for both pristine and irradiated samples have been carried out at room temperature, series resistance and barrier heights for both as deposited and irradiated samples were extracted. The barrier height was found to vary from 0·73–0·54 eV. The series resistance varied from 102·04–38·61 kΩ.     

Electrical characteristics and inhomogeneous barrier analysis of aniline green/p-Si heterojunctions

In this study, we identically prepared the aniline green/p-Si organic–inorganic devices (total 27 diodes) formed by direct evaporation of an organic compound solution on to a p-Si semiconductor wafer, and then studied the current–voltage (I–V) and capacitance–voltage (C–V) characteristics of these devices. It was seen that the aniline green organic thin film on the p-Si substrate showed a good rectifying behavior. The barrier heights (BHs) and ideality factors of all devices were extracted from the electrical characteristics. Mean BH and ideality factor were calculated as 0.582 eV and 2.999, respectively from the I–V characteristics. Additionally, the mean barrier height and mean acceptor doping concentration from C–V measurements were calculated as (0.61 ± 0.10) eV and (5.54 ± 0.68) × 10¹⁴ cm⁻³, respectively. The discrepancy in the BH values obtained from I–V and C–V characteristics has been attributed to different nature of the measurements. This can also be due to the existence of the interfacial native oxide and the organic aniline green thin layer between the semiconductor and contacting top metal.     

Laser-induced surface decomposition of Al2O3 excited in the V-center absorption band

The primary products of desorption from Al₂O₃ surface excited by laser pulses (pulse duration τ∼15 ns; wavelength λ=354 nm, radiant power density P/S<10⁸ W/cm²) in the V-center absorption band were studied by the time-of-flight (TOF) spectroscopy. The TOF spectra show evidence of the desorption of one “ cold” (T ₁=300 K) and two “hot” (T ₂=1000 K, T ₃=4300 K) groups of oxygen molecules with the Maxwell velocity distributions, as well as of the hot Al and O atoms with nonequilibrium energy distributions (E ₁=0.37 eV, E ₂=0.38 eV). A model describing the oxygen desorption as initiated by the electron transitions is suggested, in which escape of the cold O₂ molecules from the surface is related to discharge of the O ₂ ⁻ anions adsorbed on the V-centers, desorption of the hot atoms is attributed to discharge of the surface O⁻ anions, and the appearance of the hot O² molecules is related to the associative desorption of two O⁻ anions localized at the same V-center discharged by a pair of excitons.     

Microwave-stimulated relaxation of internal strains in GaAs-based device heterostructures

We have studied the effect of microwave radiation (frequency, 2.45 GHz; specific power density, 1.5 W/cm²) on the relaxation of internal mechanical strains in the (i)n-n ⁺-GaAs structures, (ii) Au-Ti-n-n ⁺-GaAs diode structures with Schottky barriers, and (iii) GaAs-based Schottky-barrier field-effect transistors (SFETs). It is shown that exposure of the samples to the microwave radiation for a few seconds leads to relaxation of the internal mechanical strains and improves the quality of the semiconductor surface layer structure. This results in improved parameters of the GaAs-based device structures of both (diode and SFET) types, as manifested by increased Schottky barrier height, reduced ideality factor and back current in the diode structures, and increased gain slope and initial drain current in the SFETs.     

Enhancement of thermal stability of TiO2 nanowires embedded in anodic aluminum oxide template

Titania (TiO₂) nanowires with diameters of 20, 50, and 80 nm were successfully synthesized via the template-assistant method. The TiO₂ nanowires embedded in anodic aluminum oxide template have extremely high crystallization and anatase-to-rutile phase transition temperatures than that of the free-state TiO₂ powders, and the thermal stability of embedded TiO₂ nanowires depends on the diameter of the templates. The growth and nucleation activation energy of rutile in 20 nm nanowires are determined to be _boxclose E_{\rm{g}}  = 2.8 ± 0.2 eV and E_n E_{\rm{n}}  = 2.7 ± 0.2 eV, respectively, much higher than that of the free-state TiO₂ powders with E_g E_{\rm{g}}  = 1.6 ± 0.2 eV and E_n E_{\rm{n}}  = 1.9 ± 0.2 eV. The pressure induced by the difference of thermal expansion coefficient between the TiO₂ and aluminum oxide acts as an effective barrier that prevents phase transition, resulting in the enhancement of the TiO₂ structural stability.     

Structural and electrical characteristics of epitaxial InP layers on porous substrates and the parameters of related Au-Ti Schottky barriers

The structures comprising three epitaxial InP layers—buffer (n ⁺⁺), active (n), and contact (n ⁺)—were grown by liquid phase epitaxy on porous and compact (control) InP(100) substrates. High quality of the active n-InP layer obtained on a porous substrate (in comparison to the control samples) is confirmed by the values of the halfwidths of the (311) X-ray diffraction reflections (54″ versus 76″), dislocation concentration (5×10²−5×10³ cm⁻² versus 5×10⁴−5×10⁵ cm⁻²), and electron mobility (4000 cm²/V s versus 3000–3500 cm²/V s). Using these homoepitaxial InP structures, Au-Ti Schottky diodes with a working mesastructure area of ∼1.8￠10⁻⁶ cm² were prepared. It was found that diodes based on the porous substrates are characterized by significantly smaller leak currents and higher breakdown voltages as compared to those of the control diodes: 1 nA, 27 V versus 200 nA, 15 V.     

Photodiodes based on <Emphasis Type="Italic">n</Emphasis>-GaSb/<Emphasis Type="Italic">n</Emphasis>-GaInAsSb/<Emphasis Type="Italic">p</Emphasis>-AlGaAsSb heterostructures grown using rare-earth elements for the 1.1–2.4 μm spectral range

Photodiodes sensitive in the wavelength range of 1.1–2.4 μm have been created based on n-GaSb/n-GaInAsSb/p-AlGaAsSb heterostructures with a narrow-gap n-GaInAsSb layer (E _g ≅ 0.5 eV) grown in the presence of a rare-earth element (holmium). The electron concentration in the narrow-gap layer is n = 1 × 10¹⁶ cm⁻³, which is about one-fourth of that in an analogous structure grown without the rare-earth element. The proposed structure is characterized by increased quantum efficiency and response speed.     

Development of the bubble technique for the measurement of the surface energy of solids

A method for the measurement of the surface energy of copper at 500† C is described. Argon or krypton gas is introduced into a thin surface layer of a specimen by an ion implantation process and subsequent annealing precipitates this gas. At equilibrium the gas pressure in the small bubbles formed is balanced by the surface tension forces andγ=1560±160 erg cm⁻² has been measured.     

Deep surface states on the interface between SiC and its native thermal oxide

Deep surface states are discovered on the interface between 6H-SiC and its native thermal oxide by analyzing the C-V characteristics of metal-oxide-semiconductor structures measured at a high temperature (600 K). The maximum of the density of states distributed according to energy (D _tm=2×10¹² cm⁻²· eV⁻¹) is at an energy about 1.2 eV below the bottom of the conduction band of SiC. It is postulated that the states discovered are similar in nature to the P _b centers observed in the SiO₂/Si system. Pis’ma Zh. Tekh. Fiz. 23, 55–60 (October 26, 1997)     

Observation of Multiple Gap Structures Using NdFeAsO<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>F<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>–GaAs Tunneling Junction

We have carried out point contact tunneling measurements by contacting degenerated GaAs semiconductor to polycrystalline samples of NdFeAsO_1−x F _x with T _c=44−51±1.2. The obtained conductance curves have plural structures included in energy region of the superconducting gap. These structures are seen at almost the same bias positions on every measurement. And as temperature increases, the structures are smeared out. Thus, the structures are attributed to multiple gap structures. The gap values are Δ _S=6.3±0.3 meV, Δ _L=12.5±0.5 meV and 2Δ _S/k _B T _c=3.1±0.3, 2Δ _L/k _B T _c=6.2±0.7. Separately from these multiple gap structures, some fine structures are seen in outer energy region of the gap structures. We have calculated d² I/dV ² and T _c from using conventional s-wave Eliashberg equations by appropriately assuming α ² F(ω). The phonon positions of the calculated d² I/dV ² curve are in quite good agreement with that of experimental result. Moreover, the calculated T _c reproduces the experimental one.     

The effect of annealing on the electroluminescence of SiO<Subscript>2</Subscript> layers with excess silicon

We have studied the effect of annealing on the electroluminescence (EL) spectrum of Si-SiO₂ structures containing excess ion-implanted silicon in the oxide layer. The implantation of 150-keV silicon ions to doses in the range from 5×10¹⁶ to 3×10¹⁷ cm⁻² leads to the appearance of an intense emission band at 2.7 eV in the EL spectrum. The postimplantation annealing leads to a decrease in the intensity of this band and to the appearance of a new EL band at 1.6 eV assigned to radiative transitions in defect centers formed at the boundaries between silicon nanoclusters and silicon dioxide.     

An electron spin resonance study of Mn2+ doped calcium hydrazine carboxylate monohydrate

Single crystals of calcium hydrazine carboxylate, monohydrate have been studied by ESR of Mn²⁺ doped in the calcium sites. X-band ESR indicated a large crystal field splitting necessitating experiments at Q band. The analysis shows two magnetically inequivalent (but chemically equivalent) sites withg _xx = 2.0042±0.0038,g _yy=2.0076 ±0.0029,g _zz=2.0314±0.001,A _zz=0.0099±0.0002 cm⁻¹,A _xx=0.0092±0.0002 cm⁻¹,A _yy=0.0082±0.0002 cm⁻¹,D=3/2D _zz=0.0558±0.0006 cm⁻¹, andE=1/2 (D _yy−D _yy)=0.0127±0.0002 cm⁻¹. One of the principal components of the crystal field, (D _zz), is found to be along the Ca ↔ Ca direction in the structure and a second one, (D _xx), along the perpendicular to the plane of the triangle formed by three neighbouring calciums. TheA tensor is found to have an orientation different from that of theg andD tensors reflecting the low symmetry of the Ca²⁺ sites.     

The parameters of laser plasmas formed using polycrystalline CuInS<Subscript>2</Subscript>, copper,and indium targets

We have studied the electron temperature (T _e) and density (N _e) of laser plasmas formed under the action of a neodymium laser in a polycrystalline CuInS₂ target, as well as in pure copper and indium targets. At a laser beam power density of ∼10⁸ W/cm², the average electron temperature of a laser plasma at a distance of r=1 mm from the CuInS₂ target falls within 0.55–0.77 eV, while the laser plasmas of copper and indium are characterized by T _e(Cu)=0.4–1.8 eV and T _e(In)=0.58–2.4 eV, respectively. The average electron density at the core of the laser torch (r=1 mm) at the CuInS₂ target reaches N _e=2.2×10¹⁶ cm⁻³. The results obtained for the polycrystalline target can be used in microelectronics for optimization of the process of laser deposition of thin films for solar cell elements.