Fabrication and characterization of in situ polymerized n-polyaniline films grown on p-Si heterojunctions

This work presents a study on the fabrication and the electrical transport mechanism of the in situ polymerized n-type polyaniline (PANI) grown on p-type Si to form n-polyaniline/p-Si heterojunction devices. The current-voltage-temperature (I-V-T) characteristics of n-PANI/p-Si devices were investigated in the temperature range of 298-373 K. These devices showed good rectifying behavior and the temperature dependence of the I-V characteristics were successfully explained by the thermionic mechanism in the narrow potential range, V ? 0.4 V. The barrier height, ideality factor and the series resistance values of this structure were obtained from the forward bias I-V characteristics. The capacitance-voltage-temperature (C-V-T) characteristics of n-PANI/p-Si devices were also investigated. The barrier height values obtained from the C-V measurements were found to be higher than that obtained from the I-V measurements at various temperatures. From the capacitance-voltage-frequency (C-V-f) characteristics, it was found that the capacitance remained almost constant up to a certain values of the frequency in the lower and higher sides of the frequency scale. The higher values of capacitance at low frequencies were attributed to the excess capacitance resulting from the interface states in equilibrium with the p-Si side that can follow the AC signal.     

Electrical analysis of Al/ZnO/p-Si,Al/PMMA/p-Si and Al/PMMA/ZnO/p-Si structures: Comparison study

Al/ZnO/p-Si, Al/PMMA/p-Si and Al/PMMA/ZnO/p-Si structures were fabricated. Based on the measured current–voltage (C–V) and capacitance–voltage curves, the electrical characteristics of these heterostructures such as ideality factor, barrier height and series resistance of each structure were analyzed and then compared with those of Al/PMMA/ZnO/p-Si. According to C–V measurement, it was found that the Al/PMMA/ZnO/p-Si structure indicates the better electronic performance rather than other structures. The obtained results represent low series resistance (19.3 Ω) after coating with polymethyl methacrylate (PMMA) over ZnO/p-Si heterojunction structure for Al/PMMA/ZnO/p-Si heterostructure.     

Fabrication and electrical properties of Al/aniline green/n-Si/AuSb structure

The current–voltage (I–V), capacitance–voltage (C–V) and capacitance–frequency (C–f) characteristics of Al/aniline green(AG)/n-Si/AuSb structure were investigated at room temperature. A modified Norde's function combined with conventional forward I–V method was used to extract the parameters including barrier height (BH) and the series resistance. The barrier height and series resistance obtained from Norde's function was compared with those from Cheung functions, and it was seen that there was a good agreement between the BH values and series resistances from both methods. The C–V characteristics were performed at 10 and 500 kHz frequencies, and C–f characteristics were performed 0.0, +0.4 and −0.4 V.     

Analysis of the Temperature Dependence of the Capacitance–Voltage and Conductance–Voltage Characteristics of Au/TiO2(rutile)/n-Si Structures

The capacitance–voltage–temperature (C–V–T) and the conductance/angular frequency–voltage–temperature (G/ω–V–T) characteristics of Au/TiO₂(rutile)/n-Si Schottky barrier diodes (SBDs) were investigated over the temperature range from 200 K to 380 K by considering the series resistance effect. Titanium dioxide (TiO₂) was deposited on n-type silicon (Si) substrate using a direct-current (DC) magnetron sputtering system at 200°C. To improve the crystal quality, the deposited film was annealed at 900°C to promote a phase transition from the amorphous to rutile phase. The C ^?2 versus V plots gave a straight line in the reverse-bias region. The main electrical parameters, such as the doping concentration (N _D), Fermi energy level (E _F), depletion layer width (W _D), barrier height (ф _CV), and series resistance (R _S), of Au/TiO₂(rutile)/n-Si SBDs were calculated from the C–V–T and the G/ω–V–T characteristics. The obtained results show that ф _CV, R _S, and W _D values decrease, while E _F and N _D values increase, with increasing temperature.     

Electrical parameters of a DC sputtered Mo/n-type 6H-SiC Schottky barrier diode

A Mo/n-type 6H-SiC/Ni Schottky barrier diode (SBD) was fabricated by sputtering Mo metal on n-type 6H-SiC semiconductor. Before the formation of Mo/n-type 6H-SiC SBD, an ohmic contact was formed by thermal evaporation of Ni on n-type 6H-SiC and annealing at 950 °C for 10 min. It was seen that the structure had excellent rectification. The electrical parameters were extracted using its current–voltage (I–V) and capacitance–voltage (C–V) measurements carried out at room temperature. Very high (1.10 eV) barrier height and 1.635 ideality factor values were reported for Mo/n-type 6H-SiC using ln I–V plot. The barrier height and series resistance values of the diode were also calculated as 1.413 eV and 69 Ω from Norde׳s functions, respectively. Furthermore, 1.938 eV barrier height value of Mo/n-type 6H-SiC SBD calculated from C–V measurements was larger than the one obtained from I–V data.     

Influence of Annealing on Electrical Properties of an Organic Thin Layer-Based n-Type InP Schottky Barrier Diode

The electrical properties of a fabricated Au/polymethylmethacrylate (PMMA)/n-InP Schottky barrier diode have been analyzed for different annealing temperatures using current–voltage (I–V) and capacitance–voltage (C–V) techniques. It is observed that the Au/PMMA/n-InP structure shows excellent rectifying behavior. The extracted barrier height and ideality factor of the as-deposited Au/PMMA/n-InP Schottky contact are 0.68 eV (J–V)/0.82 eV (C–V) and 1.57, respectively. However, the barrier height (BH) of the Au/PMMA/n-InP Schottky contact increases to 0.78 eV (J–V)/0.99 eV (C–V) when the contact is annealed at 150°C for 1 min in nitrogen atmosphere. Upon annealing at 200°C, the BH value decreases to 0.72 eV (J–V)/0.90 eV (C–V) and the ideality factor increases to 1.48. The PMMA layer increases the effective barrier height of the structure by creating a physical barrier between the Au metal and the n-InP. Cheung’s functions are also used to calculate the series resistance of the Au/PMMA/n-InP structure. The interface state density (N _ss) is found to be 6.380 × 10¹² cm^?2 eV^?1 and 1.916 × 10¹² cm^?2 eV^?1 for the as-deposited and 150°C-annealed Au/PMMA/n-InP Schottky contacts, respectively. These results indicate that the interface state density and series resistance have a significant effect on the electrical characteristics of Au/PMMA/n-InP Schottky barrier devices. Finally, it is noted that the diode parameters change with increasing annealing temperature.     

Extraction of electronic parameters of Schottky diode based on an organic Orcein

An Au/Orcein/p-Si/Al device was fabricated and the current-voltage measurements of the devices showed diode characteristics. Then the current-voltage (I-V), capacitance-voltage (C-V) and capacitance-frequency (C-f) characteristics of the device were investigated at room temperature. Some junction parameters of the device such as ideality factor, barrier height, and series resistance were determined from I-V and C-V characteristics. The ideality factor of 2.48 and barrier height of 0.70 eV were calculated using I-V characteristics. It has been seen that the Orcein layer increases the effective barrier height of the structure since this layer creates the physical barrier between the Au and the p-Si. The interface state density N_ss were determined from the I-V plots. The capacitance measurements were determined as a function of voltage and frequency. It was seen that the values of capacitance have modified with bias and frequency.     

Electrical characterization and DLTS analysis of a gold/n-type gallium nitride Schottky diode

This work describes a comparison of current density–voltage (J–V) and capacitance–voltage (C–V) properties measured as a function of temperature; deep trap properties are measured by deep level transient spectroscopy (DLTS) of Schottky diodes fabricated on n-type gallium nitride (GaN grown by metal organic vapor phase epitaxy (MOVPE). Unexpected behavior in the standard Richardson plot was observed in the temperature range 165–480 K, reflecting a range of Schottky barrier heights and a variation of ideality factor. This was explained by applying a Gaussian spatial distribution of barrier heights across the Schottky diode. C–V measurements were carried out in the temperature range 165–480 K to compare the temperature dependence of the barrier height with those obtained by the Gaussian distribution method. DLTS and high-resolution Laplace DLTS (LDLTS) show a majority carrier peak centered at 450 K.     

Electrical and photoelectrical characterization of an organic–inorganic heterojunction based on quinoline yellow dye

An organic–inorganic contact was fabricated by forming a thin film of quinoline yellow dye (QY) on a p-Si wafer and evaporating Al metal on the film. The current–voltage (I–V) and capacitance–voltage (C–V) measurements of Al/QY/p-Si heterostructure were applied in dark and room temperature to calculate the characteristic parameters of diode like ideality factor, barrier height and series resistance. Ideality factor and barrier height values were found as 1.23 and 0.87 eV from I–V data, respectively. The series resistance value of the device was determined as 1.8 kΩ by using modified Norde function. The C–V measurements were carried out at different frequencies and it was seen that capacitance value decreased with increasing frequency. Interface state density distribution was calculated by means of I–V measurement. In addition the optical absorption of thin QY film on glass was measured and optical band gap of the film was found as 2.73 eV. Furthermore, I–V measurements of Al/QY/p-Si/Al were taken under illumination between 40 and 100 mW/cm². It was observed that reverse bias current of the device increased with light intensity. Thus, the heterojunction had a strong response to the light and it can be suitable for electrical and optoelectronic applications like a photodiode.     

Determination of the laterally homogeneous barrier height of palladium Schottky barrier diodes on n-Ge (1 1 1)

We have studied the experimental linear relationship between barrier heights and ideality factors for palladium (Pd) on bulk-grown (1 1 1) Sb-doped n-type germanium (Ge) metal-semiconductor structures with a doping density of about 2.5×10¹⁵ cm^?3. The Pd Schottky contacts were fabricated by vacuum resistive evaporation. The electrical analysis of the contacts was investigated by means of current–voltage (I–V) and capacitance–voltage (C–V) measurements at a temperature of 296 K. The effective barrier heights from I–V characteristics varied from 0.492 to 0.550 eV, the ideality factor n varied from 1.140 to 1.950, and from reverse bias capacitance–voltage (C^?2–V) characteristics the barrier height varied from 0.427 to 0.509 eV. The lateral homogenous barrier height value of 0.558 eV for the contacts was obtained from the linear relationship between experimental barrier heights and ideality factors. Furthermore the experimental barrier height distribution obtained from I–V and (C^?2?V) characteristics were fitted by Gaussian distribution function, and their mean values were found to be 0.529 and 0.463 eV, respectively.     

Electrical characteristics of Pd Schottky contacts on ZnO films

The electrical characteristics of Pd Schottky contacts on ZnO films have been investigated by current-voltage (I–V) and capacitance–voltage (C–V) measurements at different temperatures. ZnO films of two thicknesses (400 nm and 1000 nm) were grown by DC-magnetron sputtering on n-Si substrates. The basic structural, optical and electrical properties of these films are also reported. We compared the two Schottky diodes by means of characteristic parameters, such as rectification ratio, ideality factor (η), barrier height (Φ_b) and series resistance and obtained better results for the 1000 nm-ZnO Schottky diodes. We also discussed the dependence of I‐V characteristics on temperature and the two distinct linear regions observed at low temperatures are attributed to the existence of two different inhomogeneous barrier heights. From I–V plots in a log-log scale we found that the dominant current-transport mechanism at large forward bias is space-charge limited current (SCLC) controlled by the presence of traps within the ZnO bandgap. The existence of such traps (deep states or interface states) is demonstrated by frequency-dependent capacitance and deep-level transient spectroscopy (DLTS) measurements.     

Electrical characterization of cobalt phthalocyanine/p-silicon heterojunction

We report the fabrication of organic/inorganic heterojunction of cobalt phthalocyanine (CoPc) with p-type silicon (p-Si) using vacuum thermal evaporation. At ambient conditions, the electrical characteristics of the heterojunction are investigated. The optical band gap of CoPc is calculated from absorption spectrum using Tauc׳s law. The electrical characterization of the heterojunction shows rectifying behavior with a rectification ratio (RR) of 316. Different diode parameters are extracted from the current–voltage (I–V) curves, such as ideality factor n, barrier height ϕ, series resistance R_s and shunt resistance R_sh. These parameters are in good agreement with those calculated from the functions of Cheungs and Norde . The conduction of charge carriers through the interface of p-Si/CoPc is also studied. The fabricated heterojunction could be a promising candidate for its potential use in electronic applications.     

Current–voltage and capacitance–voltage characteristics of Al Schottky contacts to strained Si-on-insulator in the wide temperature range

The electrical characteristics of Al/strained Si-on-insulator (sSOI) Schottky diode have been investigated using current–voltage (I–V) and capacitance–voltage (C–V) measurements in the wide temperature range of 200–400 K in steps of 25 K. It was found that the barrier height (0.57–0.80 eV) calculated from the I–V characteristics increased and the ideality factor (1.97–1.28) decreased with increasing temperature. The barrier heights determined from the C–V measurements were higher than those extracted from the I–V measurements, associated with the formation of an inhomogeneous Schottky barrier at the interface. The series resistance estimated from the forward I–V characteristics using Cheung and Norde methods decreased with increasing temperature, implying its strong temperature dependence. The observed variation in barrier height and ideality factor could be attributed to the inhomogeneities in Schottky barrier, explained by assuming Gaussian distribution of barrier heights. The temperature-dependent I–V characteristics showed a double Gaussian distribution with mean barrier heights of 0.83 and 1.19 eV and standard deviations of 0.10 and 0.16 eV at 200–275 and 300–400 K, respectively. From the modified Richardson plot, the modified Richardson constant were calculated to be 21.8 and 29.4 A cm⁻² K⁻² at 200–275 and 300–400 K, respectively, which were comparable to the theoretical value for p-type sSOI (31.6 A cm⁻² K⁻²).     

Electrical properties of Au–Sb/p-GaSe:Gd Schottky barrier diode

Experimental results of the fabricated Schottky barrier diode on a GaSe:Gd substrate are presented. The electrical analysis of Au–Sb/p-GaSe:Gd structure has been investigated by means of current–voltage (I–V) and capacitance–voltage (C–V) measurements at 296 K temperature. The diode ideality factor and the barrier height have been obtained to be 1.07 and 0.85 eV, respectively, by applying a thermionic emission theory. At high currents in the forward direction, the series resistance effect has been observed. The series resistance has been determined from I–V measurements using Cheung's method.     

Characteristics of the Schottky barriers of two-terminal thin-film Al/nano-Si film/ITO structures

The temperature dependence of the Schottky-barrier height and series resistance of two-terminal thin-film Al/nano-Si film/ITO structures are determined from the current—voltage (I–V) characteristics in the temperature range of 20–150°C. It is found that the form of the I–V characteristic at all investigated temperatures can be described by a model of two Schottky diodes connected back-to-back. For these diodes, the general formula is obtained, which allows the construction of functions approximating experimental curves with high accuracy. Based on this formula, a computational model is built, which generalizes the theoretical data obtained by S.K. Cheung and N.W. Cheung widely used for analyzing the I–V characteristics of single Schottky diodes. A technique is developed for calculating the Schottky-barrier heights in a system of two Schottky diodes connected back-to-back, their ideality factors, and the series resistance of the system. It is established that the barrier heights in the investigated temperature range are ~1 eV. According to the temperature dependence of the barrier height, such large values result from the presence of a SiO _x (0 ≤ x ≤ 2) oxide layer at the nanoparticle boundaries. Charge carriers can overcome this layer by means of thermal excitation or tunneling. It is established that the intrinsic Schottky-barrier height of the Al/nc-Si film and nc-Si film/ITO junctions is ~0.1 eV. The activation dependences of the series resistance of the Al/nc-Si film/ITO structures and impedance spectra show that combined electric-charge transport related to ionic and electronic conductivity takes place in the structures under study. It is shown that the contribution of the electronic conductivity to the total transport process increases as the sample temperature is raised.     

Electrical,photovoltaic and photosensitivity characteristics of p-ZnTe:N/CdTe:Mg/n-CdTe:I/GaAs for photodiode applications

In this work, heterojunctions of p-ZnTe:N/CdTe:Mg/n-CdTe:I/GaAs for photovoltaic and photodiode application were grown epitaxially by using molecular beam system. Current-voltage profile of the heterojunction device was studied in dark and under various illumination intensities. The obtained photocurrent is found to depend on the light intensity. The main heterojunction parameters, such as shunt and series resistances, the barrier height and the ideality factor were extracted from the current-voltage profile using diverse methods at ambient temperature. Values of the barrier height and the series resistance were obtained from Cheung's functions. A large value of the series resistance causes the non-ideal characteristics of current–voltage measurements. The study of the current-voltage characteristics of high voltage region suggests a predominant space charge limited mechanism. Moderate values of short circuit current and open circuit voltage were obtained through a light intensity of 140 mW/cm², a current and voltages of 0.336 mA and 370 mV, respectively. The high photosensitivity and responsivity for the current under illumination condition suggests that the prepared heterojunction device could be employed as a photodiode sensor.     

The effects of thermal annealing on the electrical characteristics of Au/n–InP/In diode

An Au/n–InP/In diode has been fabricated in the laboratory conditions and the current–voltage (I–V) and capacitance–voltage (C–V) characteristics of the diode have been measured in room temperature. In order to observe the effect of the thermal annealing, this diode has been annealed at temperatures 100 and 200 °C for 3 min in N₂ atmosphere. The characteristic parameters such as leakage current, barrier height and ideality factor of this diode have been calculated from the forward bias I–V and reverse bias C–V characteristics as a function of annealing temperature. Also the rectifying ratio of the diode is evaluated for as-deposited and annealed diode.     

On the profile of temperature dependent series resistance in Al/Si3N4/p-Si (MIS) Schottky diodes

The temperature dependence of capacitance-voltage (C-V) and conductance-voltage (G/w-V) characteristics of metal-insulator-semiconductor (Al/Si₃N₄/p-Si) Schottky barrier diodes (SBDs) was investigated by considering series resistance effect in the temperature range of 80-300 K. It is found that in the presence of series resistance, the forward bias C-V plots exhibit a peak, and experimentally show that the peak positions with a maximum at 260 K shift toward lower voltages with increasing temperature. The C-V and (G/w-V) characteristics confirm that the interface state density (N_ss) and series resistance (R_s) of the diode are important parameters that strongly influence the electric parameters of MIS structures. The crossing of the G/w-V curves appears as an abnormality compared to the conventional behavior of ideal Schottky diode. It is thought that the presence of series resistance keeps this intersection hidden and unobservable in homogeneous Schottky diodes, but it appears in the case of inhomogeneous Schottky diode. In addition, the high frequency (C_m) and conductance (G_m/w) values measured under both reverse and forward bias were corrected for the effect of series resistance to obtain the real diode capacitance.     

Characterization of an Au/n-Si photovoltaic structure with an organic thin film

We demonstrate that a copper(II) organic complex can control the electrical characteristics of conventional Au/n-Si metal–semiconductor (MS) contacts. We investigated the electronic and photovoltaic properties of a Cu(II) complex/n-Si heterojunction diode. The ideality factor n and barrier height Φ_b of the diode were 2.22 and 0.736 eV, respectively. An ideality factor greater than unity indicates that the diode exhibits non-ideal current–voltage behavior. This behavior results from the effect of series resistance and the presence of an interfacial layer. The series resistance and barrier height determined using Norde’s method were 6.7 kΩ and 0.77 eV, respectively. The device showed photovoltaic behavior, with a maximum open-circuit voltage of 0.24 V and a short circuit current of 1.7 μA under light of 8 mW/cm².     

Effect of series resistance on the electrical characteristics and interface state energy distributions of Sn/p-Si (MS) Schottky diodes

In this study, electrical characteristics of the Sn/p-type Si (MS) Schottky diodes have been investigated by current-voltage (I-V) and capacitance-voltage (C-V) measurements at room temperature. The barrier height obtained from C-V measurement is higher than obtained from I-V measurement and this discrepancy can be explained by introducing a spatial distribution of barrier heights due to barrier height inhomogeneities, which are available at the nanostructure Sn/p-Si interface. A modified Norde’s function combined with conventional forward I-V method was used to extract the parameters including barrier height (Φ_b) and the series resistance (R_S). The barrier height and series resistance obtained from Norde’s function was compared with those from Cheung functions. In addition, the interface-state density (N_SS) as a function of energy distribution (E_SS-E_V) was extracted from the forward-bias I-V measurements by taking into account the bias dependence of the effective barrier height (Φ_b) and series resistance (R_S) for the Schottky diodes. While the interface-state density (N_SS) calculated without taking into account series resistance (R_S) has increased exponentially with bias from 4.235 × 10¹² cm⁻²eV⁻¹ in (E_SS - 0.62) eV to 2.371 × 10¹³ cm⁻²eV⁻¹ in (E_SS - 0.39) eV of p-Si, the N_SS obtained taking into account the series resistance has increased exponentially with bias from of 4.235 × 10¹² to 1.671 × 10¹³ cm⁻²eV⁻¹ in the same interval. This behaviour is attributed to the passivation of the p-doped Si surface with the presence of thin interfacial insulator layer between the metal and semiconductor.