Photovoltaic characteristics of Au/PVA (Bi-doped)/n-Si Schottky barrier diodes (SBDs) at various temperatures

The charge conduction properties of the Au/PVA (Bi-doped)/n-Si Schottky barrier diodes (SBDs) were investigated using current–voltage–temperature (I–V–T) measurements in dark and under various illumination levels. For this purpose, the main diode parameters such as reverse-saturation current (I_o), zero-bias barrier height (Φ_Bo), ideality factor (n), series resistance (R_s) and shunt resistance (R_sh) of diode were obtained as function of temperature and illumination level. Experimental results show that all of these electrical parameters are strong functions of illumination and temperature. The change in all electrical parameters becomes more important at low temperatures and illumination levels. While the n value decreases with increasing temperature and illumination level, Φ_Bo value increases. The fill factor (FF = V_m·I_m/V_oc·I_sc) values were obtained as 0.34 at 80 K and 0.40 at 320 K under 50 W and these values are near to a photodiode. Therefore, the fabricated diode can be used as a photodiode in optoelectronic applications. The forward bias I–V characteristics of the diode have also been explained by the space charge limited current (SCLC) model.     

Electrical characterization of Au/poly (linoleic acid)-g-poly(methyl methacrylate) (PLiMMA)/n-Si diode in dark and under illumination

In this study, poly (linoleic acid)-g-poly(methyl methacrylate) (PLiMMA) graft copolymer is used as an interfacial layer in a Schottky diode for the first time. Au/poly (linoleic acid)-g-poly(methyl methacrylate) (PLiMMA)/n-Si diode was fabricated and main electrical characteristics of the diode were investigated using I–V measurements in dark and under illumination at room temperature. Ideality factor (n), barrier height (Φ_B0) and serial resistance (R_s) values of the diode were found as 2.8, 0.87 eV and 8096 Ω for dark, and 6.3, 0.71 eV and 676 Ω for 100 mW/cm² illumination intensity. Also, the reasons of deviation from ideal thermionic emission theory were investigated using Cheung&Cheung method and Card&Rhoderick's function which are used for calculating voltage dependence of barrier height (Φ_B(V)), series resistance (R_s) and number of surface states (N_ss) of the Au/PLiMMA/n-Si diode.     

Electrical characteristics of p-Si/TiO2/Al and p-Si/TiO2-Zr/Al Schottky devices

Electrical devices involve different types of diode in prospective electronics is of great importance. In this study, p-type Si surface was covered with thin film of TiO₂ dispersion in H₂O to construct p-Si/TiO₂/Al Schottky barrier diode (D1) and the other one with TiO₂ dispersion doped with zirconium to construct p-Si/TiO₂-Zr/Al diode (D2) by drop-casting method in the same conditions. Electrical properties of as-prepared diodes and effect of zirconium as a dopant were investigated. Current–voltage (I–V) characteristics of these devices were measured at ambient conditions. Some parameters including ideality factor (n), barrier height (Φ_B0), series resistance (Rs) and interface state density (Nss) were calculated from I–V behaviours of diodes. Structural comparisons were based on SEM and EDX measurements. Experimental results indicated that electrical parameters of p-Si/TiO₂/Al Schottky device were influenced by the zirconium dopant in TiO₂.     

Illumination dependence of I-V and C-V characterization of Au/InSb/InP(1 0 0) Schottky structure

The effects of surface preparation and illumination on electric parameters of Au/InSb/InP(100) Schottky diode were investigated, in the later diode InSb forms a fine restructuration layer allowing to block In atoms migration to surface. In order to study the electric characteristics under illumination, we make use of an He-Ne laser of 1 mW power and 632.8 nm wavelength. The current-voltage I(V_G), the capacitance-voltage C(V_G) measurements were plotted and analysed. The saturation current I_s, the serial resistance R_s and the mean ideality factor n are, respectively, equal to 2.03 × 10⁻⁵ A, 85 Ω, 1.7 under dark and to 3.97 × 10⁻⁵ A, 67 Ω, 1.59 under illumination. The analysis of I(V_G) and C(V_G) characteristics allows us to determine the mean interfacial state density N_ss and the transmission coefficient θ_n equal, respectively, to 4.33 × 10¹² eV⁻¹ cm⁻², 4.08 × 10⁻³ under dark and 3.79 × 10¹² eV⁻¹ cm⁻² and 5.65 × 10⁻³ under illumination. The deep discrete donor levels presence in the semiconductor bulk under dark and under illumination are responsible for the non-linearity of the C⁻²(V_G) characteristic.     

Electrical and photovoltaic characteristics of sodium copper chlorophyllin/n-type silicon heterojunctions

Heterojunctions of p-type sodium copper chlorophyllin (p-SCC)/n-type silicon (n-Si) were prepared by deposition of p-SCC film on n-Si wafers using spray-pyrolysis technique. Current-voltage and capacitance-voltage measurements of Au/p-SCC/n-Si/In heterojunctions were performed to discuss the electrical properties of these heterostructures. Rectifying characteristics were observed, which are definitely of the diode type. The current-voltage measurements suggest that the forward current in these junctions involves tunnelling and the results showed that the forward current can be explained by a multi-tunnelling capture-emission model in which the electron emission process dominates the carrier transport mechanism. On the other hand, the reverse current is probably limited by the same conduction process. The capacitance-voltage behavior indicates an abrupt heterojunction model is valid for Au/p-SCC/n-Si/In heterojunctions and the junction parameters such as, built-in potential, V_D, carrier concentration, N, the width of depletion layer, W, were obtained. The temperature and frequency dependence of the measured capacitance were also studied. The loaded I-V characteristics under white illumination provided by tungsten lamp (80 mW/cm²) give values of 400 mV, 0.9 mA, 0.38 and 1.7% for the open-circuit voltage, V_oc, the short-circuit current, I_sc, the fill factor, FF, and conversion efficiency, η, respectively.     

Investigation of current transport parameters of Ti/4H-SiC MPS diode with inhomogeneous barrier

The current transport parameters of 4H-SiC merged PiN Schottky(MPS) diode are investigated in a temperature range of 300-520 K.Evaluation of the experimental current-voltage(I-V) data reveals the decrease in Schottky barrier height Φ b but an increase in ideality factor n,with temperature decreasing,which suggests the presence of an inhomogeneous Schottky barrier.The current transport behaviours are analysed in detail using the Tung’s model and the effective area of the low barrier patches is extracted.It is found that small low barrier patches,making only 4.3% of the total contact,may significantly influence the device electrical characteristics due to the fact that a barrier height of 0.968 eV is much lower than the average barrier height 1.39 eV.This shows that ion implantation in the Schottky contact region of MPS structure may result in a poor Ti/4H-SiC interface quality.In addition,the temperature dependence of the specific on-resistance(R on sp),T 2.14,is determined between 300 K and 520 K,which is similar to that predicted by a reduction in electron mobility.     

Investigation of photo-induced change of electro-optical performance in a liquid crystal-organic field effect transistor (LC-OFET)

This study aimed to improve the electrical characteristics of poly(3-hexylthiophene) (P3HT) and liquid crystal-organic field effect transistors (LC-OFETs) under UV illumination. Consequently, a novel LC-OFET was fabricated using a nematic liquid crystal (E63) and a P3HT mixture in an OFET cell. Cell thickness was determined through field emission scanning electron microscopy. For assessment of the electrical characteristics, the LC-OFET device was exposed to various UV light intensities in total darkness for the purpose of obtaining the output- and transfer-current voltage. The capacitance–frequency plot of the capacitor cell was then measured to determine the main parameters including the threshold voltage (V_Th), field effect mobility (μ_FET) and current on/off ratio (I_on/off) of the device. Thus, the full characterisation and UV light response of the electronic parameters were determined for this new class of transistors. Results showed that the new LC-OFET exhibited good performance in the form of low V_Th, high μ_FET, and high I_on/off.     

Analysis of dark current contributions in mercury cadmium telluride junction diodes

An analytical approach to analyze the dark current–voltage (I–V) and dynamic impedance vs reverse bias voltage (R_d–V) characteristics of an HgCdTe junction diode is presented in this paper. Application to the experimental data is discussed to illustrate the approach. It is shown that the relative contributions of the various dark current contributing mechanisms viz. diffusion, generation–recombination, thermal trap assisted tunneling, band-to-band tunneling, avalanche multiplication and ohmic current component can all be isolated, if present.     

Effect of ambient temperature on electrical properties of nanostructure n-ZnO/p-Si heterojunction diode

The nanostructure n-ZnO/p-Si heterojunction diode was fabricated by sol–gel method. The structural and morphological properties of the nanostructure ZnO film have been investigated. The X-ray diffraction spectra indicated that the films are of polycrystalline nature. The scanning electron microscopy images indicate that the surface morphology of ZnO film is almost homogeneous and the ZnO film is consisted of the circular formed with coming together of the nanoparticles. The electrical characterization of nanostructure n-ZnO/p-Si heterojunction diode has been investigated by current–voltage characteristics. The ideality factor (n) of the diode was found for different ambient temperatures and the obtained 6.40 value for 296 K is higher than unity due to the interface states between the two semiconductor materials and series resistance. The values of n increased with decreasing ambient temperature. The reverse current of the diode increased with illumination intensity of 100 mW cm⁻² and the diode gave a maximum open circuit voltage V_oc of 0.19 V and short-circuits current I_sc of 8.03 × 10⁻⁸ A.     

Photovoltaic characterization of n-CdTe/p-CdMnTe/GaAs diluted magnetic diode

A CdTe/CdMnTe heterojunction magnetic diode for photovoltaic applications was fabricated by using molecular beam epitaxy (MBE). The ideality factor and the potential barrier height of the diode were determined to be 1.25 and 0.836 eV, respectively. Photovoltaic parameters of the studied device were determined at various illumination intensities. The highest open circuit voltage of the CdTe/CdMnTe heterostructure was equal to 0.56 V at the illumination intensity of 130 mW/cm². The reverse current of the n-CdTe/p-CdMnTe/GaAs diode increases with the increasing illumination intensities. The obtained results suggest that n-CdTe/p-CdMnTe/GaAs diode can be used as a photodiode in photovoltaic and photodetector applications.     

Two diodes model and illumination effect on the forward and reverse bias I–V and C–V characteristics of Au/PVA (Bi-doped)/n-Si photodiode at room temperature

The forward and reverse bias current–voltage (I–V), capacitance/conductance–voltage (C/G–V) characteristics of the fabricated Au/PVA (Bi-doped)/n-Si photodiode have been investigated both in dark and under 250 W illumination intensity at room temperature. The energy density distribution profile of N_ss was extracted from the forward bias I–V measurements by taking the voltage dependence of effective barrier height (Φ_e) and R_s for photodiode both in dark and under 250 W illumination cases. The exponential growth of the N_ss from midgap toward the bottom of the conductance band is very apparent for two cases. The obtained high value of n and R_s were attributed to the particular distribution of N_ss at metal/PVA interface, surface and fabrication processes, barrier inhomogeneity of interfacial polymer layer and the form of barrier height at M/S interface. While the values of C and G/w increase R_s and R_sh decrease under illumination, due to the illumination induced electron–hole pairs in depletion region. The voltage dependent N_ss profile was also obtained from the dark and illumination capacitance at 1 MHz and these values of N_ss are in good agreement. In addition, the fill factor (FF) under 250 W illumination level was found as 28.5% and this value of FF may be accepted sufficiently high. Thus, the fabricated Au/PVA (Bi-doped)/n-Si structures are more sensitive to light, proposing them as a good candidate as a photodiode or capacitance sensor for optoelectronic applications in modern electronic industry.     

Neutron irradiation effects on I–V characteristics of Au/n-GaAs Schottky diodes

Diodes are one of the most important and widely used components of electronic circuits. These devices can be damaged especially when they are used in radiation fields whose effects depend on radiation type and energy. To investigate these effects, the Au/n-GaAs type Schottky diodes have been irradiated by neutrons emitted from a ²⁵²Cf source which provides neutrons at an average energy of 2.14 MeV. The diode parameters barrier height (Φ_b0), ideality factor (n) and series resistance (R_s) have been obtained from forward current–voltage (I–V) characteristics before and after irradiation and the results are discussed.     

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.     

Electrical properties of Al/p–Ge and Al/Methyl Green/p–Ge diodes

Methyl green (MG) film has been grown for the first time on p–Ge semiconductor using a simple and low-cost drop coating method. The current–voltage (I–V) characteristics of Al/p–Ge and Al/MG/p–Ge diodes have been investigated in the temperature range of 20–300 K. A potential barrier height as high as 0.82 eV has been achieved for Al/MG/p–Ge diode, which has high rectification rate, at room temperature. It is seen that the barrier height of the Al/MG/p–Ge diode at the room temperature is larger than that of Al/p–Ge diode and ideality factor value of 1.14 calculated for Al/MG/p–Ge diode is lower than Al/p–Ge diode. The temperature coefficient of barrier height of the Al/MG/p–Ge diode has been calculated as 2.6 meV/K. The evaluation of current–voltage characteristics shows that the barrier height of the diode increases with the increasing temperature.     

TiO2 Nanotube Array/Monolayer Graphene Film Schottky Junction Ultraviolet Light Photodetectors

Schottky junctions made from a titanium dioxide nanotube (TiO₂NT) array in contact with a monolayer graphene (MLG) film are fabricated and utilized for UV light detection. The TiO₂NT array is synthesized by the anodization and the MLG through a simple chemical vapor deposition process. Photoconductive analysis shows that the fabricated Schottky junction photodetector (PD) is sensitive to UV light illumination with good stability and reproducibility. The corresponding responsivity (R), photoconductive gain (G), and detectivity (D*) are calculated to be 15 A W^?1, 51, and 1.5 × 10¹² cm Hz^1/2 W^?1, respectively. It is observed that the fabricated PD exhibits spectral sensitivity and a simple power‐law dependence on light intensity. Moreover, the height of the Schottky junction diode is derived to be 0.59 V by using a low temperature I–V measurement. Finally, the working mechanism of the TiO₂NT array/MLG film Schottky junction PD is elucidated.     

Study of anti-clockwise bipolar resistive switching in Ag/NiO/ITO heterojunction assembly

The anti-clockwise bipolar resistive switching in Ag/NiO/ITO (Indium–Tin–Oxide) heterojunctional thin film assembly is investigated. A sequential voltage sweep in 0 → V _max → 0 → ?V _min → 0 order shows intrinsic hysteresis behaviour and resistive switching in current density (J)–voltage (V) measurements at room temperature. Switching is induced by possible rupture and recovery of the conducting filaments in NiO layer mediated by oxygen ion migration and interfacial effects at NiO/ITO junction. In the high-resistance OFF-state space charge limited current passes through the filamentary path created by oxygen ion vacancies. In OFF-state, the resistive switching behaviour is attributed to trapping and detrapping processes in shallow trap states mostly consisting of oxygen vacancies. The slope of Log I vs Log V plots, in shallow trap region of space charge limited conduction is ~2 (I ∝ V ²) followed by trap-filled and trap-free conduction. In the low-resistance ON-state, the observed electrical features are governed by the ohmic conduction.     

Analysis of current–voltage and capacitance–voltage characteristics of perylene-monoimide/n-Si Schottky contacts

The electrical and interface state properties of Au/perylene-monoimide (PMI)/n-Si Schottky barrier diode have been investigated by current–voltage (I–V) and capacitance–voltage (C–V) measurements at room temperature. A good rectifying behavior was seen from the I–V characteristics. The series resistance (R_s) values were determined from I–V and C–V characteristics and were found to be 160 Ω and 53 Ω, respectively. The barrier height (Φ_b) of Au/PMI/n-Si Schottky diode was found to be 0.694 eV (I–V) and 0.826 eV (C–V). The ideality factor (n) was obtained to be 4.27 from the forward bias I–V characteristics. The energy distribution of interface state density (N_ss) of the PMI-based structure was determined, and the energy values of N_ss were found in the range from E_c ? 0.508 eV to E_c ? 0.569 eV with the exponential growth from midgap toward the bottom of the conduction band. The values of the N_ss without R_s are 2.11 × 10¹² eV^?1 cm^?2 at E_c ? 0.508 eV and 2.00 × 10¹² eV^?1 cm^?2 at E_c ? 0.569 eV. Based on the above results, it is clear that modification of the interfacial potential barrier for metal/n-Si structures has been achieved using a thin interlayer of the perylene-monomide.     

Molecular control over Ag/p-Si diode by organic layer

Electrical transport properties of Ag metal-fluorescein sodium salt (FSS) organic layer-silicon junction have been investigated. The current-voltage (I-V) characteristics of the diode show rectifying behavior consistent with a potential barrier formed at the interface. The diode indicates a non-ideal I-V behavior with an ideality factor higher than unity. The ideality factor of the Ag/FSS/p-Si diode decreases with increasing temperature and the barrier height increases with increasing temperature. The barrier height (φ_b=0.98 eV) obtained from the capacitance-voltage (C-V) curve is higher than barrier height (φ_b=0.72 eV) derived from the I-V measurements. The barrier height of the Ag/FSS/p-Si Schottky diode at the room temperature is significantly larger than that of the Ag/p-Si Schottky diode. It is evaluated that the FSS organic layer controls electrical charge transport properties of Ag/p-Si diode by excluding effects of the SiO₂ residual oxides on the hybrid diode.     

The effect of interface states, excess capacitance and series resistance in the Al/SiO2/p-Si Schottky diodes

The current-voltage (I-V) characteristics of Al/SiO₂/p-Si metal-insulator-semiconductor (MIS) Schottky diodes were measured at room temperature. In addition the capacitance-voltage (C-V) and conductance-voltage (G-V) measurements are studied at frequency range of 10 kHz-1 MHz. The higher value of ideality factor of 3.25 was attributed to the presence of an interfacial insulator layer between metal and semiconductor and the high density of interface states localized at Si/SiO₂ interface. The density of interface states (N_ss) distribution profile as a function of (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_e) at room temperature for the Schottky diode on the order of ≅4 × 10¹³ eV⁻¹ cm⁻²_. These high values of N_ss were responsible for the non-ideal behaviour of I-V and C-V characteristics. Frequency dispersion in C-V and G-V can be interpreted only in terms of interface states. The N_ss can follow the ac signal especially at low frequencies and yield an excess capacitance. Experimental results show that the I-V, C-V and G-V characteristics of SD are affected not only in N_ss but also in series resistance (R_s), and the location of N_ss and R_s has a significant on electrical characteristics of Schottky diodes.     

Fabrication and electrical characterization of p-Sb2S3/n-Si heterojunctions for solar cells application

Antimony trisulphide (Sb₂S₃) films were prepared by thermal evaporation technique on n-type single crystal Si substrates to fabricate p-Sb₂S₃/n-Si heterojunctions. The electrical transport properties of the p–Sb₂S₃/n-Si heterojunctions were investigated by current–voltage (I–V) and capacitance–voltage (C–V) measurements. The temperature-dependent I–V characteristics revealed that the forward conduction was determined by multi-step tunnelling current and the activation energy of saturation current was about 0.54 eV. The 1/C²–V plots indicated the junction was abrupt and the junction built-in potential was 0.6 V at room temperature and decreased with increasing temperature. The solar cell parameters have been calculated for the fabricated cell as V_oc = 0.50 V, J_sc = 14.53 mA cm⁻², FF = 0.32 and η = 4.65% under an illumination of 50 mW cm⁻².