Study and modeling of the transport mechanism in a semi insulating GaAs Schottky diode

The current through a metal–semiconductor junction is mainly due to the majority carriers. Three distinctly different mechanisms exist in a Schottky diode: diffusion of carriers from the semiconductor into the metal, thermionic emission–diffusion (TED) of carriers across the Schottky barrier and quantum–mechanical tunneling through the barrier. The insulating layer converts the MS device in an MIS device and has a strong influence on its current–voltage (I–V) and the parameters of a Schottky barrier from 3.7 to 15 eV. There are several possible reasons for the error that causes a deviation of the ideal behavior of Schottky diodes with and without an interfacial insulator layer. These include the particular distribution of interface states, the series resistance, bias voltage and temperature. The GaAs and its large concentration values of trap centers will participate in an increase of the process of thermionic electrons and holes, which will in turn the IV characteristic of the diode, and an overflow maximum value [NT = 3 × 10²⁰] is obtained. The I–V characteristics of Schottky diodes are in the hypothesis of a parabolic summit.     

The study of optical,dielectric and optoelectronic properties of dodecylbenzene sulfonic acid doped polyaniline

Soluble polyaniline (PANI) doped with dodecylbenzene sulfonic acid (DBSA) was synthesized by chemical oxidation method and was cast on glass using homemade spray, a simple technology used for coating thin film in order to replace other costly complicated techniques. The PANI–DBSA was characterized by FTIR, XRD and UV–vis techniques. The TGA results illustrated that they are three major stages of weight loss of the PANI–DBSA sample. D.C. and A.C. study was performed by pelletizing the sample. D.C. conductivity obtained at room temperature was 3.753 × 10⁻³ S/cm. The A.C. conductivity and dielectric properties was analyzed in the frequency range 100–1000 kHz which indicates that the value of dielectric constant and loss tangent increases with increase in temperature and decreases with increase in frequency and in addition it supports the hopping mechanism. Current density–voltage (J–V) measurements was used to characterize ITO/PANI–DBSA/Al device. The value of various junction parameters such as ideality factor, barrier height and saturation current density was calculated.     

Analysis of the electrical properties of p–n GaAs homojunction under dc and ac fields

In this work, the n-type GaAs films were grown on p-type GaAs single crystalline substrate by metal organic chemical vapor deposition (MOCVD). The temperature dependence of the current density–voltage (J–V) characteristics of n-GaAs/p-GaAs homojunction contacts were measured in the temperature range 293–413 K. These characteristics showed a rectifying behavior consistent with a potential barrier formed at the interface. The forward current density–voltage characteristics under low voltage biasing were explained on the basis of thermionic emission mechanism. The high values of ideality factor (n) may be ascribed to the presence of an interfacial layer. Analysis of the experimental data under the reverse voltage biasing suggests a dominant mechanism was found to be a Schottky effect. The impedance properties and the alternating current (ac) conductivity of n-GaAs/p-GaAs homojunction were investigated as a function of frequency and temperature. The ac conductivity was found to obey the universal power law. The variation of the exponent s with the temperature suggested that the conduction mechanism is an overlapping large-polaron tunneling (OLPT) model associated with correlated barrier hopping (CBH) model at the higher temperature.     

Electrical properties and Schottky diodes using N-N′diphenyl-1-4phenylenediamine

Thin films of, N-N′diphenyl 1-4phenylene-diamineane are prepared using vacuum sublimation technique. The electrical conductivity from room temperature down to 127 K is studied. It is found that the conduction of charge carriers obeys T^−1/2 dependence on temperature. The average hopping distance, hopping energy, density of states and their variation due to post-deposition heat treatment are studied. Schottky diodes are fabricated with gold as ohmic contact and aluminium as Schottky contact. From the observed current voltage characteristics the saturation current density, diode ideality factor and the barrier height are determined. Their variation with air annealing is also investigated.     

Unipolar conductivity of SrTiO<Subscript>3</Subscript> crystals with light-induced drop in electrical resistance

This paper reports on the results of the experimental investigation of unipolar (diode) current–voltage characteristics of local regions in high-resistance SrTiO₃ crystals that experienced a light-induced drop in electrical resistance. This behavior has been explained by the influence exerted on the electrical conductivity by the irradiated region in the Schottky barrier of one of the contacts. The ideality factor of the Schottky barrier has been determined and the barrier height for a number of regions has been estimated from measurements of the forward branch of the current–voltage characteristics. An analysis of the specific features in the behavior of the reverse branch of the current–voltage characteristics has revealed that, in the SrTiO₃ crystals with p-type conductivity, the resistance switching occurs through a pure electronic mechanism, in contrast to models based on electrochemical processes, in particular, the migration of oxygen vacancies.     

Magnetically tunable nonlinear current–voltage characteristics in oxygen deficient manganite perovskites

La_0.667Ca_0.333Mn_1−xM_xO_3−δ (M=Mg, Li or Re) exhibit insulating behaviour and nonlinear current–voltage (J–E) relationship with voltage-limiting characteristics at temperatures below the ferromagnetic transition (T_c). The high current region is set in at field strengths <60 V/cm. Nonlinearity exponent, α in the relation J=kE^α increases inversely with temperature. In presence of an external magnetic field, the J–E curves show higher current density at lower field strengths. Microstructural studies indicate that there is no segregation of secondary phases in the grain boundary regions. There is remarkable changes in ρ(T) as well as J–E curves with the grain size. Annealing studies in lower p_O2 atmospheres indicate that there is significant out-diffusion of oxygen ions through the grain boundary layer (GBL) regions creating oxygen vacancies in the GBL regions. The concentration of Mn⁴⁺ ions is lowered at the GBL due to oxygen vacancies, reducing the probability of hopping and resulting in insulating behaviour. Therefore an insulating barrier is introduced between two conducting grains and the carrier motion between the grains is inhibited. Thus below T_c, where sufficient increase in resistivity is observed the conduction may be arising as a result of spin dependent tunneling across the barrier. External electric field lowers the barrier height and establishes carrier transport across the barrier. Above certain field strength, barrier height diminishes significantly and thereby allowing large number of carriers for conduction, giving rise to highly nonlinear conductivity.     

Electrical conductivity behaviour of pure and polyblends samples of polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA)

Electrical conductivity of pure PVC, PMMA and their polyblends samples has been studied in detail as a function of polarizing fields at constant temperatures. Different plots were drawn to investigate the nature of mechanism responsible for conduction. The nature of all the thermograms is nonlinear but similar for all temperatures. The plots have two slopes, i.e., ohmic conduction with slope of curve ≈1 at lower voltage region and a non-ohmic conduction with slope ≈1.9 at higher voltage region are observed. The increase in the conductivity and decrease in the activation energy, suggest that plasticization effect is taking place between the polymers when they are blended. Fowler–Nordheim plots are not consistent and showing negative and positive slopes simultaneously for lower as well as higher values of applied voltage. Theoretical and experimental values of β_SR and β_PF were calculated and the β_exp of pure and polyblend samples is in agreement with theoretically β_PF. The β_exp value lies close to β_PF, this shows that Poole–Frenkel mechanism is also effective. The calculated metal electrode potential barrier at a constant voltage suggests that the dominant charge carrier mechanism is Schottky–Richardson type. Hence in the present case both SR and PF mechanisms are seem to be operative.     

AC conductivity and dielectric behavior of bulk Furfurylidenemalononitrile

AC conductivity and dielectric behavior for bulk Furfurylidenemalononitrile have been studied over a temperature range (293–333 K) and frequency range (50–5×10⁶ Hz). The frequency dependence of ac conductivity, σ_ac, has been investigated by the universal power law, σ_ac(ω)=Aω^s. The variation of the frequency exponent (s) with temperature was analyzed in terms of different conduction mechanisms, and it was found that the correlated barrier hopping (CBH) model is the predominant conduction mechanism. The temperature dependence of σ_ac(ω) showed a linear increase with the increase in temperature at different frequencies. The ac activation energy was determined at different frequencies. Dielectric data were analyzed using complex permittivity and complex electric modulus for bulk Furfurylidenemalononitrile at various temperatures.     

Charge carrier transport and d.c. conductivity in thin polycrystalline p-terphenyl films2

The electrical conductivity and charge carrier mobility in thin polycrystalline p-terphenyl layers have been measured. The transport and conductivity were interpreted in terms of a hopping mechanism. The activation energies of mobility and conductivity were obtained, and the density of states in the vicinity of the Fermi level 10²⁰ cm^?3 eV^?1 was estimated. The height of the potential barrier around the impurity levels changed according to the Poole-Frenkel effect.     

Effect of series resistance on the performance of silicon Schottky diode in the presence of tin oxide layer

The current–voltage (I–V) characteristics of Al/SnO₂/p-Si (MIS) Schottky diodes prepared by means of spray deposition method have been measured at 80, 295 and 350 K. In order to interpret the experimentally observed non-ideal Al/SnO₂/p-Si Schottky diode parameters such as, the series resistance R_s, barrier height Φ_B and ideality factor n, a novel calculation method has been reported by taking into account the applied voltage drop across interfacial oxide layer V_i and ideality factor n in the current transport mechanism. The values obtained for V_i were subtracted from the applied voltage values V and then the values of R_s were recalculated. The parameters obtained by accounting for the voltage drop V_i have been compared with those obtained without considering the above voltage drop. It is shown that the values of R_s estimated from Cheung’s method were strongly temperature-dependent and decreased with increasing temperature. It is shown that the voltage drop across the interfacial layer will increase the ideality factor and the voltage dependence of the I–V characteristics. The interface state density N_ss of the diodes has an exponential growth with bias towards the top of the valance band for each temperature; for example, from 2.37 × 10¹³ eV⁻¹ cm⁻² in 0.70−E_v eV to 7.47 × 10¹³ eV⁻¹ cm⁻² in 0.62−E_v eV for 295 K. The mean N_ss estimated from the I–V measurements decreased with increasing the temperature from 8.29 × 10¹³ to 2.20 × 10¹³ eV⁻¹ cm⁻².     

Conduction mechanism and the dielectric relaxation process of a-Se75Te25−xGax (x=0, 5, 10 and 15 at wt%) chalcogenide glasses

Se₇₅Te_25−xGa_x (x=0, 5, 10 and 15 at wt%) chalcogenide compositions were prepared by the well known melt quenching technique. Thin films with different thicknesses in the range (185–630 nm) of the obtained compositions were deposited by thermal evaporation technique. X-ray diffraction patterns indicate that the amorphous nature of the obtained films. The ac conductivity and the dielectric properties of the studied films have been investigated in the frequency range (10²–10⁵ Hz) and in the temperature range (293–333 K). The ac conductivity was found to obey the power low ω^s where s≤1 independent of film thickness. The temperature dependence of both ac conductivity and the exponent s can be well interpreted by the correlated barrier hopping (CBH) model. The experimental results of the dielectric constant ε₁ and dielectric loss ε₂ are frequency and temperature dependent. The maximum barrier height W_m calculated from the results of the dielectric loss according to the Guintini equation, and agrees with that proposed by the theory of hopping of charge carriers over a potential barrier as suggested by Elliott for chalcogenide glasses. The density of localized state was estimated for the studied film compositions. The variation of the studied properties with Ga content was also investigated. The correlation between the ac conduction and the dielectric properties were verified.     

Degraded model of radiation-induced acceptor defects for GaN-based high electron mobility transistors （HEMTs）

Using depletion approximation theory and introducing acceptor defects which can characterize radiation induced deep-level defects in AlGaN/GaN heterostructures, we set up a radiation damage model of AlGaN/GaN high electron mobility transistor (HEMT) to separately simulate the effects of several main radiation damage mechanisms and the complete radiation damage effect simultaneously considering the degradation in mobility. Our calculated results, consistent with the experimental results, indicate that thin AlGaN barrier layer, high Al content and high doping concentration are favourable for restraining the shifts of threshold voltage in the AlGaN/GaN HEMT; when the acceptor concentration induced is less than 10¹⁴cm^-3, the shifts in threshold voltage are not obvious; only when the acceptor concentration induced is higher than 10¹⁶cm^-3, will the shifts of threshold voltage remarkably increase; the increase of threshold voltage, resulting from radiation induced acceptor, mainly contributes to the degradation in drain saturation current of the current--voltage (I--V) characteristic, but has no effect on the transconductance in the saturation area.     

Electrical impedance and conduction mechanism analysis of biopolymer electrolytes based on methyl cellulose doped with ammonium iodide

In the present study, the potential of methyl cellulose (MC) as biopolymer electrolyte (BPE) will be studied extensively by means of conductivity and the conduction mechanism. BPE films based on MC doped with ammonium iodide (NH₄I) salt were prepared by solution-casting method. X-ray diffraction (XRD) explains that the conductivity enhancement of the electrolytes is affected by the degree of crystallinity. Field emission scanning electron microscopy (FESEM) analysis shows the difference in the electrolyte’s surface with respect to NH₄I. On addition of 40 wt.% of NH₄I, the highest room temperature conductivity of (5.08?±?0.04)?×?10^?4 S cm^?1 was achieved. The temperature dependence relationship for the salted electrolyte was found to obey the Arrhenius rule where R² ～1 from which the activation energy (E _a) was evaluated. The dielectric study analyzed using complex permittivity ε* for the sample with the highest conductivity at elevated temperature shows a non- Debye behavior. These salted electrolytes follow the correlated barrier hopping (CBH) model.     

Effect of annealing temperature on the electrical properties of Au/Ta2O5/n-GaN metal–insulator–semiconductor (MIS) structure

We report on the effect of an annealing temperature on the electrical properties of Au/Ta₂O₅/n-GaN metal–insulator–semiconductor (MIS) structure by current–voltage (I–V) and capacitance–voltage (C–V) measurements. The measured Schottky barrier height (Φ _bo) and ideality factor n values of the as-deposited Au/Ta₂O₅/n-GaN MIS structure are 0.93 eV (I–V) and 1.19. The barrier height (BH) increases to 1.03 eV and ideality factor decreases to 1.13 upon annealing at 500 ^°C for 1 min under nitrogen ambient. When the contact is annealed at 600 ^°C, the barrier height decreases and the ideality factor increases to 0.99 eV and 1.15. The barrier heights obtained from the C–V measurements are higher than those obtained from I–V measurements, and this indicates the existence of spatial inhomogeneity at the interface. Cheung’s functions are also used to calculate the barrier height (Φ _bo), ideality factor (n), and series resistance (R _s ) of the Au/Ta₂O₅/n-GaN MIS structure. Investigations reveal that the Schottky emission is the dominant mechanism and the Poole–Frenkel emission occurs only in the high voltage region. The energy distribution of interface states is determined from the forward bias I–V characteristics by taking into account the bias dependence of the effective barrier height. It is observed that the density value of interface states for the annealed samples with interfacial layer is lower than that of the density value of interface states of the as-deposited sample.     

Electrical conduction and dielectric studies of ZnO pellets

A series of Zinc Oxide pellets sintered at different temperatures was studied by means of dielectric spectroscopy in the wide frequency range of 1–10⁶ Hz and temperature interval from −100 °C to 30 °C. Electrical conductivity was analysed using Jonsher's universal power law, and the values of s were found to decrease with the increase in temperature, which agrees well with the correlation barrier hopping (CBH) model.     

Properties of Mott contacts with an ultralow metal-semiconductor barrier

The current-voltage and capacitance characteristics of Mott contacts with an ultralow metal-semiconductor barrier are investigated. The analysis is based on the analytical solution of the Poisson equation for the space charge of carriers in the “metal-i-layer-n ⁺-substrate” structure without regard for bulk doping of the i layer. For contacts with ultralow metal-semiconductor barriers (comparable in magnitude to the thermal energy of charge carries), it is demonstrated that the reverse current becomes greater than the forward current, the sign of rectification is reversed, and the capacitance of the contact acquires a strong dependence on the voltage. This means that the mechanism of nonlinearity of the structure changes and the nonlinearity governed by charge carriers injected into the i layer becomes dominant. In a specific range of bias voltages close to zero, the differential resistance and the capacitance of the structure exponentially increase with increasing voltage. The observed behavior is not typical of conventional metal-semiconductor contacts. The obtained dependences of the electric current and capacitance on the voltage determine the characteristics of new advanced instruments, in particular, highly sensitive microwave detectors operating without a bias voltage.     

Effect of annealing on the electronic parameters of Au/poly(ethylmethacrylate)/n-InP Schottky diode with organic interlayer

A thin poly(ethylmethacrylate) (PEMA) layer is deposited on n-InP as an interlayer for electronic modification of Au/n-InP Schottky structure. The electrical properties of Au/PEMA/n-InP Schottky diode have been investigated by current–voltage (I–V) and capacitance–voltage (C–V) measurements at different annealing temperatures. Experimental results show that Au/PEMA/n-InP structure exhibit a good rectifying behavior. An effective barrier height as high as 0.83 eV (I–V) and 1.09 eV (C–V) is achieved for the Au/PEMA/n-InP Schottky structure after annealing at 150 °C compared to the as-deposited and annealed at 100 and 200 °C. Modified Norde's functions and Cheung method are also employed to calculate the barrier height, series resistance and ideality factors. Results show that the barrier height increases upon annealing at 150 °C and then slightly decreases after annealing at 200 °C. The PEMA layer increases the effective barrier height of the structure as this layer creates a physical barrier between the Au metal and the n-InP. Terman's method is used to determine the interface state density and it is found to be 5.141 × 10¹² and 4.660 × 10¹² cm^?2 eV^?1 for the as-deposited and 200 °C annealed Au/PEMA/n-InP Schottky diodes. Finally, it is observed that the Schottky diode parameters change with increasing annealing temperature.     

Transition voltage spectroscopy: Artefacts of the Simmons approach

The initial interpretation of the transition voltage (V_t) spectroscopy within a tunneling barrier picture has been later challenged within calculations based on the Simmons model. In this communication, it will be shown that the predictions of the Simmons model for V_t represent artefacts of an inadequate WKB-type constant barrier approximation, which are exacerbated by those calculations by an incorrect expression of the image potential.     

Analysis of electrical characteristics of Er/p-InP Schottky diode at high temperature range

We report on the temperature-dependent electrical characteristics of Er/p-InP Schottky barrier diodes. The current–voltage (I–V) and capacitance–voltage (C–V) measurements have been carried out in the temperature range of 300–400 K. Using thermionic emission (TE) theory, the zero-bias barrier height (Φ_bo) and ideality factor (n) are estimated from I–V characteristics. It is observed that there is a decrease in n and an increase in the Φ_bo with an increase in temperature. The barrier height inhomogenity at the metal/semiconductor (MS) interface resulted in Gaussian distribution of Φ_bo and n. The laterally homogeneous Schottky barrier height value of approximately 1.008 eV for the Er/p-InP Schottky barrier diodes is extracted from the linear relationship between the experimental zero-bias barrier heights and ideality factors. The series resistance (R_s) is calculated by Chenug's method and it is found that it increases with the decrease in temperature. The reverse-bias leakage current mechanism of Er/p-InP Schottky diode is investigated. Both Poole–Frenkel and Schottky emissions are described and discussed. Furthermore, capacitance–voltage (C–V) measurements of the Er/p-InP Schottky contacts are also carried out at room temperature in dark at different frequencies of 10, 100 and 1000 kHz. Using Terman's method, the interface state density is calculated for Er/p-InP Schottky diode at different temperatures.     

Effect of impurity (Sb and Ag) incorporation on the a.c. conductivity and dielectric properties of a-Se70Te30 glassy alloy

The effect of additives (Sb and Ag) on a.c. conductivity and dielectric properties of Se₇₀Te₃₀ glassy alloy at temperature range 300-350 K and frequency range 1 kHz-5 MHz has been studied. Experimental results indicate that a.c. conductivity and dielectric parameters depend on temperature, frequency and the impurity incorporated in Se-Te glassy system. The a.c. conductivity in the aforesaid frequency range is found to obey the ω^s law. A strong dependence of a.c. conductivity and exponent s in the entire temperature and frequency range contradicts quantum-mechanical tunneling (QMT) model and can be interpreted in terms of the correlated barrier hopping (CBH) model. The temperature and frequency dependence of the dielectric parameters are also studied and it is found that the results agrees by the theory of hopping of charge carriers over potential barrier as suggested by Elliott in chalcogenide glasses. The change in the dielectric parameters with the opposite influence of the replacement of Te by Sb on the one hand, and by Ag, on the other hand is being correlated by the nature of covalent character of the studied composition and with the change in density of defect states.