High Value Of Ideality Factor Research Articles

Dark conduction mechanisms of PTQBDT based heterojunction diode

Al:LiF/PTQBT:PCBM/PEDOT:PSS/ITO/glass organic-based diode is fabricated with different weight ratios in PTQBT:PCBM active layer. The diodes D1, D2 and D3 are prepared using the precursor solution for spin coating process as 1:2, 1:3 and 1:4, respectively. Under dark, main diode parameters are extracted by conventional thermionic emission theory using the results of measurements. Parasitic resistance contribution, non-ideal barrier height formation and high values of ideality factor indicate possible effects of space charge limited current flow mechanism on forward biased characteristics. At saturated voltage region, series resistances are calculated and the results are evaluated according to Cheung’s method. The possible voltage sharing between interface layer and depletion region are also investigated by analysis of density of interface states. In addition, field effect is found in a major role on the reverse current flow and the mechanism is evaluated according to Schottky-Richardson model.

Study of electrical transport, dielectric and magnetic properties of NiFe2O4-PVDF nanocomposite film

In this study, Nickel ferrite (NiFe 2 O 4 ) nanoparticle (NFO) and Nickel ferrite - Polyvinylidene fluoride (NFO-PVDF) nanocomposite films have been synthesized by chemical route method. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirm the formation of pure phase NFO nanoparticles. The electrical transport and dielectric properties of nanocomposite film have been reported in the frequency range 200 Hz ≤ f ≤ 2 MHz and temperature range 303 ≤ T ≤ 410 K. The activation energy (E a ) and barrier height ( φ b ) are enhanced for NFO-PVDF composite film compare to pure PVDF film. The high value of ideality factor implies that the hopping charge transport mechanism is dominated in the composite film. The AC conductivity also follows correlated barrier hopping (CBH) mechanism. The dielectric permittivity increases with filler (NFO) concentration and temperature. Dielectric permittivity and electric modulus are well fitted with the modified Cole-Cole and KWW function. Non-Debye type of relaxation phenomenon is observed in higher temperature and higher filler concentration. The magnetic measurement of the NFO-PVDF composite depicts the soft ferromagnetic behaviour of the materials. The saturation magnetization and hysteresis loop area are increased in higher filler (NFO) concentration. Magnetic hysteresis study of 4% NFO-PVDF may show the ferrimagnetism with supressed saturation magnetization than pure NFO. However, the saturation magnetization and hysteresis loop area are increased in 8% filler (NFO) concentration. • Two distinct activations have been observed in the samples. • A hump is observed in temperature vs dielectric constant study. • Dielectric permittivity enhances in composites over polymer. • Hysteresis loop has been observed in NFO-PVDF composites. • Both magnetic and dielectric properties have been observed in composites.

Effect of Sb, Tb3+ Doping on Optical and Electrical Performances of SnO2 and Si Based Schottky Diodes

(Sb, Tb3+)-doped SnO2 thin films were deposited on monocrystalline silicon (Si) and on porous silicon (PS) layer from sol-gel spin coating method. The photoluminescence spectrum shows that Tb3+ ions presents higher emission with the PS layer. The fabricated junctions are treated as a metal-semiconductor (MS) Schottky diodes. The current–voltage (I-V) characteristics of SnO2:Sb/p-Si (D1), SnO2:Sb:Tb3+/p-Si (D2) and SnO2:Sb:Tb3+/PS (p) (D3) were measured for these diodes at room temperature. Electronic parameters such as ideality factor, barrier height and series resistance were calculated and compared for the main junctions. Based on the thermoionic emission model, it appears that the contacts presents non-ideal I-V behaviour with a relatively high values of ideality factor (n = 12 for Si based diode, and n = 24 for PS based diode) and a relatively large values of series resistance RS (RS = 2 103 Ω for D3). After the incorporation of Tb3+, the junction characteristics show that the formed diode exhibits high forward current density and a decrease in the series resistance RS (RS = 600 Ω for D2). The non-ideality character of the elaborated MS junctions seems to be principally due to the effects of the interface. The relatively high values of the ideality factor was attributed to the sharing of the applied voltage V by a diffusion potential (VD) across the semiconductor space charge region and a potential (Vi) devoted to the interfacial layer formed between the silicon and the tin oxide. The trapped-limited current was found to dominate the current transport mechanisms through the fabricated junctions. The above results highlight the role of the interfacial layer and interface states in the determination of the electrical performance of Sb-doped SnO2/p-Si, (Sb, Tb3+) co-doped SnO2/p-Si and (Sb, Tb3+) co-doped SnO2/PS(p). They show that the simultaneous presence of Tb3+ ions and porous silicon layer allows an obvious enhancement of both optical and electrical properties of the main junction increasing then the applicability of SnO2/silicon based devices.

Optical and electrical performance of ploypyrrol thin films and its hybrid junction applications

In this work, polypyrrole (PPy) thin films were prepared by the in-situ chemical oxidative polymerization technique. The identification of the prepared films was done by using scanning electron microscopy and X-ray diffraction. The optical characterization of PPy films was achieved to obtain the optical band gaps ( = 1.44 and 2.63 eV) and Urbach energy ( = 402 meV). The capacitance and conductance characteristics as a function of frequency at different biasing voltage show the influence of interface under AC conduction. The principle hybrid junction and photovoltaic parameters were extracted from the dark and illuminated current density-voltage characteristics. The PPy-based junction demonstrated adequate rectification behavior. The high value of ideality factor was interpreted to the interface states and the influence of inhomogeneity at the organic/inorganic interface. The results show that the PPy-based hybrid junction could be utilized as an optical sensor for the optoelectronic application.

Current Transport Properties of Monolayer Graphene/n-Si Schottky Diodes

The present work reports on the fabrication and the detailed macroscopic and nanoscale electrical characteristics of monolayer graphene/n-Si Schottky diodes. The temperature dependent electrical transport properties of monolayer graphene/n-Si Schottky diodes were investigated. Nanoscale electrical characterizations were carried out using Kelvin probe force microscopy and conducting atomic force microscopy. Most the values of ideality factor and barrier height are found to be in the range of 2.0–4.4 and 0.50–0.70 eV for monolayer graphene/n-Si nanoscale Schottky contacts. The tunneling of electrons is found to be responsible for the high value of ideality factor for nanoscale Schottky contacts.

Nanostructural, optical and heterojunction characteristics of PEDOT™/ZnO nanocomposite thin films

Poly(3,4-ethylenedioxythiophene), Tetra Methacrylate (PEDOT™)/ZnO nanocomposite thin films were fabricated by the conventional spin coating method and characterized by X-ray diffraction technique. The results indicated that ZnO nanopowder has a polycrystalline nature with a hexagonal system and mean crystallite size of 53.1 nm. The main important optical parameters were extracted by using the spectrophotometer methodology covering the range of 200–2500 nm. A direct allowed transition with the onset and fundamental energy gaps were found to be 1.9 and 3.9 eV. The current density-voltage characteristics of PEDOT™/ZnO nanocomposite film/n-Si heterojunction showed diode-like behavior. Temperature dependence of series and shunt resistances was investigated. The high value of ideality factor (η) can be referred to the influence of an interfacial layer. Temperature dependence of barrier height indicated the presence of inhomogeneous barrier at an interface which is considered to be the reason for the observed behavior of the barrier height with temperature.

Investigation of the C-V characteristics that provides linearity in a large reverse bias region and the effects of series resistance, surface states and interlayer in Au/n-Si/Ag diodes

The forward and reverse bias current-voltage (I-V), capacitance/conductance-voltage-frequency (C/G-V-f) characteristics of Au/n-Si/Ag Schottky barrier diodes (SBDs) were investigated by taking into account the effects of series resistance (Rs), surface states (Nss) and interlayer at room temperature. It is quite obvious that both C-V and G/ω-V plots showed reverse, depletion, and accumulation regions in a way that resemble those of good metal-insulator-semiconductor (MIS) type SBDs rather than those of MS type SBDs. The high value of ideality factor n = 1.907) was attributed to the existence of a native SiO2 interlayer, Nss and barrier inhomogeneity at M/S interface. The energy distribution profile of Nss was obtained from the forward bias I-V data by taking into account the voltage dependence of the effective barrier height (ΦB), n and Rs. The frequency dependent profiles of Nss and Rs were also obtained from C-V and G/ω-V data using Hill Colleman and Nicollian-Brews methods, respectively. The high values of C and G/ω at low frequency were attributed to the excess capacitance (Cex.) and conductance (Gex./ω) resulting from the Nss that could follow external ac signal. The value of ΦB obtained from the reverse bias C-V data for almost each frequency is higher than that of ΦB obtained from the forward bias I-V data. Such behavior of ΦB was attributed to the nature of measurement method. Experimental results confirmed that Nss and Rs are quite effective on the electrical characteristics in the existence of native or deposited interlayer.

Study of Current-voltage Characteristic Using Deep Level Transient Spectroscopy Technique of Schottky Diode Made of SIC

Current spectroscopy was employed to investigate Silicon Carbide (SiC). DLTS standard setup was performed to study the current voltage measurement of respective schottky diode. The current voltage measurement of SiC schottky diode was carried out at different temperatures keeping the same biasing setting. From these measurements the behavior of the material is: The ideality factor of SiC at room temperature was found to be 1.9894 that was little bit improved i.e. ~ 1.7268 when temperature was increased ~400K. However values increased with decrease in temperature for the material. The higher value of ideality factor is attributed to high diffusion or tunneling current. The barrier height of SiC at room temperature was calculated as 0.995eV which remained nearly constant with increase in temperature. The change in the barrier height is related to the effective leakage current at high temperature. Reverse saturation current calculated for SiC at room temperature was 6.5706 ×10 -13 A. Its value increased up to 1.72×10 -9 A at 400K.

Study of Current-voltage Characteristic Using Deep Level Transient Spectroscopy Technique of Schottky Diode Made of SIC

Current spectroscopy was employed to investigate Silicon Carbide (SiC). DLTS standard setup was performed to study the current voltage measurement of respective schottky diode. The current voltage measurement of SiC schottky diode was carried out at different temperatures keeping the same biasing setting. From these measurements the behavior of the material is: The ideality factor of SiC at room temperature was found to be 1.9894 that was little bit improved i.e. ~ 1.7268 when temperature was increased ~400K. However values increased with decrease in temperature for the material. The higher value of ideality factor is attributed to high diffusion or tunneling current. The barrier height of SiC at room temperature was calculated as 0.995eV which remained nearly constant with increase in temperature. The change in the barrier height is related to the effective leakage current at high temperature. Reverse saturation current calculated for SiC at room temperature was 6.5706 ×10 -13 A. Its value increased up to 1.72×10 -9 A at 400K.

Optical and electrical characterization of ZnO/CuO heterojunction solar cells

This paper reports the fabrication and characterization of nontoxic heterojunction of ZnO/CuO. The films were characterized through X-ray diffraction, UV spectroscopy and field emission scanning electron microscope (FESEM). The valence and conduction band edges were measured through Photo-Electron spectroscopy in air. The electrical parameter for FTO/ZnO/CuO/In heterojunction diode such as ideality factor, barrier height, and series resistance were calculated by using conventional forward bias I–V characteristics and also verified with the help of Cheung method. The high value of ideality factor was attributed to high series resistance, defects, other phases of CuO and recombination at interface and within bulk. The double logarithmic graph of current and voltage showed that the transport mechanism is due to the space charge limited current and trapped charge limited current. Photovoltaic parameters Voc of ∼190mV and Jsc of ∼0.40mA/cm2 of FTO/ZnO/CuO/In heterojunction were recorded.

Temperature dependent current–voltage and photovoltaic properties of chemically prepared (p)Si/(n)Bi2S3 heterojunction

Ni-doped nanocrystalline Bi2S3 thin film is deposited on boron doped single crystal (p)-Si substrate by chemical bath deposition to form (p)Si/(n)Bi2S3 heterojunction structure. The electrical characterization of the (p)Si/(n)Bi2S3 heterojunction is carried out in the temperature range of 300 K–340 K and capacitance–voltage characteristics is measured at a frequency of 1 KHz at 300 K. Various junction parameters are calculated from the I–V characteristics. The ideality factor is found to be greater than unity with high series resistance. The ideality factor and series resistance decreases, whereas the saturation current density increases with increase in temperature. The J–V characteristics under illumination showed poor photovoltaic effect of the junction. The existence of higher value of ideality factor and large number of interface states in (p)Si/(n) Bi2S3 heterojunction reduced the photovoltaic conversion efficiency.

Morphological and crystalline structural characteristics of PEDOT™/TiO2 nanocomposites for applications towards technology in electronic devices

Nanocomposites of Poly(3,4-ethylenedioxythiophene), Tetra Methacrylate (PEDOT™)/TiO2 were prepared and characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Scanning electron microscopy indicated highly dense surface morphology of the prepared samples. Transmission electron microscopy images indicated that the prepared samples have particle size comparable with those obtained by X-ray diffraction results. The crystallite sizes, lattice strain and other related physical parameters were calculated by using X-ray peak broadening analysis. Optical constants such as extinction coefficient and refractive index as well as dielectric constants were calculated for PEDOT™/TiO2 nanocomposite film using spectrophotometric measurements of both transmittance and reflectance in the wavelength range of 300–2400 nm. PEDOT™/TiO2 nanocomposite films/n-Si diodes were prepared by spin coating method. The electrical properties of the diodes were investigated at different temperatures in the range 300–375 K. The prepared diode showed a rectification characteristics and the rectification ratio was studied as a function of voltage at different temperatures. Temperature dependence of both ideality factor and barrier height was also investigated. High values of ideality factor confirmed the abnormality characteristics of the prepared diodes as compared to the conventional behavior of ideal diode.

Dislocation-assisted tunnelling of charge carriers across the Schottky barrier on the hydride vapour phase epitaxy grown GaN

Barrier height and Ideality factor of Ni/n-GaN Schottky diodes are measured by performing temperature dependent current-voltage measurements. The measured value of barrier height is found to be much smaller than the theoretically calculated Schottky-Mott barrier height for the Ni/n-GaN diodes. Furthermore, a high value of ideality factor (>2) is measured at low temperatures. In order to understand these results, we need to consider a double Gaussian distribution of barrier height where the two components are related to the thermionic emission and thermionic filed emission mediated by dislocation-assisted tunnelling of carriers across the Schottky barrier. Thermionic emission is seen to dominate at temperatures higher than 170 K while the dislocation-assisted tunnelling dominates at low temperatures. The value of characteristic tunnelling energy measured from the forward bias current-voltage curves also confirms the dominance of dislocation-assisted tunnelling at low temperatures which is strongly corroborated by the Hall measurements. However, the value of characteristic tunnelling energy for high temperature range cannot be supported by the Hall results. This discrepancy can be eliminated by invoking a two layer model to analyse the Hall data which confirms that the charged dislocations, which reach the sample surface from the layer-substrate interface, provide an alternate path for the transport of carriers. The dislocation-assisted tunnelling of carriers governs the values of Schottky diode parameters at low temperature and the same is responsible for the observed inhomogeneity in the values of barrier height. The present analysis is applicable wherever the charge transport characteristics are severely affected by the presence of a degenerate layer at GaN-Sapphire interface and dislocations lines pierce the Schottky junction to facilitate the tunnelling of carriers.

Capacitance roll‐off and frequency‐dispersion capacitance–conductance phenomena in field plate and guard ring edge‐terminated Ni/SiO2/4H‐nSiC Schottky barrier diodes

In this work, field plate and guard ring edge‐terminated Ni/4H‐nSiC Schottky barrier diodes (SBD) were fabricated using standard photolithography process. Strange peaks in capacitance–conductance curves, capacitance roll‐off, and a high value of ideality factor ( = 1.3) in fabricated SBD were seen as a signature of interface trap states (Nss) at the residual oxide (2.2 nm)/4H‐nSiC interface and series resistance (Rs). Schottky capacitance spectroscopic, High–low capacitance–voltage (C–V) and forward‐bias current–voltage (I–V) techniques, in the frequency range from 100 Hz to 1 MHz, determines Nss of the order of 1012 cm−2 eV−1 and were found exponentially distributed in the bandgap of SiC. Using Hill–Coleman's method, the density Nss was calculated to be 1.15 × 1015 cm−2 eV−1 at 100 Hz and 7.81 × 1012 cm−2 eV−1 at 1 MHz, which explains the larger value of capacitance at low frequencies. Relaxation times and capture cross sections of Nss were also estimated. Calculated values of Nss were used in a Silvaco simulation that emphasize that bulk level defects present in the SiC also contributes in the experimentally observed strange peaks in C–V characteristics of fabricated SBD. At higher current levels, calculated values of Rs (V, ), confirm an increase of leakage current through residual oxide and describes the capacitance roll‐off phenomena in the fabricated SBD.

Electrical characteristics of (n)Si/(p)PbS heterojunction prepared by chemical bath deposition technique

Zn doped nanocrystalline PbS thin films is deposited on single crystal (n)-Si substrate by chemical bath deposition to form (n)Si/(p)PbS heterojunction structure. In order to study the current transport mechanism in (n)Si/(p)PbS heterojunction, the forward current–voltage characteristics is measured within the temperature 300 K – 340 K and capacitance–voltage characteristics is measured at a frequency of 1 kHz at 300 K. The forward current is greatly enhanced with increasing temperature whereas the reverse current is increased nominally. Junction parameters such as ideality factors, barrier heights, saturation current density, Richardson constant, etc. are determined from the I–V characteristics. The ideality factors are found to decrease with increase in temperature. The J–V characteristics under illumination showed poor photovoltaic effect of the junction. The higher value of ideality factor and poor photovoltaic conversion efficiency are due to the presence of interfacial layer, large series resistance and high defect density.

Characterization of InGaN by Means of I–V Measurements of Respective Light-Emitting Diode (LED) by DLTS

Indium gallium nitride (InGaN) has been characterized by means of deep-level transient spectroscopy (DLTS). The current–voltage measurement of respective schottky diode is performed by standard method available in our DLTS setup. The current–voltage measurement of InGaN is performed at various temperatures under same biasing conditions. From these measurements, the behavior of the materials is studied in detailed and listed in the following: The ideality factor, calculated to be 8.839, is found to increase with decreasing temperature of the material. However, values increased with decrease in temperature for the material. The higher value of ideality factor is attributed to high diffusion or tunneling current. The barrier height of InGaN is calculated as 0.851 eV which decreased with decrease in temperature. The change in the barrier height is related to the effective leakage current at high temperature. In InGaN, the value of reverse saturation current at room temperature is calculated as 8.22 × 10−11A, and the calculated values are found to decrease at lower temperatures.

On the electrical characteristics of the Al/rhodamine-101/p-Si MS structure at low temperatures

In this paper, the current–voltage (I–V) characteristics of Al/Rhodamine-101/p-Si/Al metal–semiconductor (MS) structures have been measured at temperatures ranging from 80 to 325K. The nonpolymeric organic compound rhodamine-101 (Rh101) film on a p-type Si substrate has been formed by means of the evaporation process and the Sn/rhodamine-101/Si contacts have been fabricated. The current–voltage characteristics of the diode show rectifying behaviour consistent with a potential barrier formed at the interface. The obtained I–V barrier heights (Φb) were in the range of 0.287–0.820eV with ideality factors (n) of 6.31–2.68. The high values of ideality factor (n) may be ascribed to decrease of the exponentially increase rate in current due to space-charge injection into Rh101 thin film at higher voltage. The temperature-dependent I–V characteristics of the Al/Rhodamine-101/p-Si/Al structure have shown a Gaussian distribution giving mean barrier height of 0.918eV and standard deviation of 0.104V. The mean barrier height (Φ¯bo) and the Richardson constant (A⁎) values were obtained as 1.046eV and 31.87AK−2cm−2, respectively, by means of the modified Richardson plot, ln[(I0/T2)–(q2σ02/2k2T2)] plot 1/kT. The value of Richardson constant A⁎ obtained from this plot is approximately the same with theoretical value of 32Acm−2K−2 for p-Si. As a result, it can be concluded that the temperature dependent characteristic parameters for Al/Rhodamine-101/p-Si structure can be successfully explained on the basis of TE mechanism with Gaussian distribution of the barrier height

Single Gaussian distribution of barrier height in Al/PS–ZnPc/p-Si type Schottky barrier diode in temperature range of 120–320 K

Possible current-transport mechanism in aluminum/polystrene–zincphthalocyanine/ptype silicon Schotky barrier diode (Al/PS–ZnPc/p-Si; SBD), for the forward bias current–voltage (I–V) characteristics were carried out in the temperature range of 120–320 K. The high value of ideality factor (n), especially at low temperatures, was attributed to the existence of PS layer, barrier in-homogeneities and particular density distribution of surface states between metal and semiconductor. An abnormal decrease in the zero-bias barrier height (BH) and increase in n with decreasing temperature which leads to non-linearity in the Richardson plot, have been observed. Linear relationship between BH and n was also observed. BH was plotted as a function of q/2kT to obtain evidence of Gaussian distribution (GD) of the BHs. The mean BH and its standard deviation (σ) were obtained as 1.03 eV and 0.117 V from the slope and intercept of this plot, respectively. Thus, the modified ln(Io/T2) − q2σo2/2k2T2 versus q/kT plot gives mean BH and the modified Richardson constant \({\text{A}}_{\bmod }^{*}\) as 1.043 eV and 29.824 A cm−2 K−2, respectively. This value of the Richardson constant is very close to the theoretical value of 32 A cm−2 K−2 for p-type Si. Therefore, non-ideal behavior of forward-bias I–V characteristics in Al/PS–ZnPc/p-Si might be successfully explained in terms of the thermionic emission mechanism with single GD of BHs.

Synthesis of 1-Dimensional CdO Nanostructures and its Heterojunction Diode Characteristics

1-Dimentional nanostrutured Cadmium Oxide (CdO) thinfilms were prepared on p-type silicon (100) substrates by Chemical Bath Deposition (CBD). Deposition time was varied form 6 hrs to 12 hrs to tune the 1-Dimensitonal nanostructures. CdO thin films deposited for 6 hrs show needle like structures whereas film deposited for 12 hrs show nanowire structure. The XRD pattern confirms the polycrystalline nature of the film. EDAX pattern confirms the elemental species with right stoichiometry. PL spectra show strong emission peak at 511nm in all the samples. n-CdO/p-Si heterojunction diode was fabricated and its characteristics were studied. Ideality factor was estimated from I-V measurements and found to be 3.5 and 3.3. This high value of ideality factor arises due to the presence of interface states and series resistance effect.

Photosensors based on Ni-doped ZnO/p-Si junction prepared by sol-gel method

A high quality and adherent transparent layer of ZnO thin films were grown on p-type Si substrates to fabricate undoped and Ni-doped ZnO/p-Si heterojunction. The C Adj −V and G Adj −V plots of the diodes are significantly affected with the frequency and Ni-dopant contents. The interface state density (D it ) is changed with the frequency and Ni contents. The high value of ideality factor (n) is due to the interface states at the interface of the diode and the effect of barrier inhomogeneities or to the high value of R s . The transient photocurrent measurements were used to analyze the photoresponse of the diodes. The obtained results indicate that the diodes could be used as an optical sensor especially for the Ni-doped at 0.5 % ZnO/p-Si diode.