Interface control and photovoltaic properties of n-type silicon/metal junction by organic dye

The electronic parameters and photovoltaic properties of the Au/methylene blue/n-Si diodes were investigated by current-voltage and capacitance-conductance-frequency techniques. The diode exhibits a non-ideal behavior due the series resistance, organic layer and oxide layer. The barrier height (1.04 eV) of the Au/methylene blue/n-Si is higher than that of Au/n-Si Schottky diode (0.83 eV) due to an excess barrier formed by organic layer. The interface state density of the diode was determined using a conductance technique and was found to be 3.25 × 10¹² eV⁻¹ cm⁻². The diode shows a photovoltaic behavior with a maximum open circuit voltage V_oc of 0.23 V and short-circuit current I_sc of 20.8 μA under 100 mW/cm². It is evaluated that Au/methylene blue/n-Si is an organic-on-inorganic photodiode with the obtained electronic parameters and methylene blue organic dye controls the interface and electrical properties of conventional metal/n-type silicon junction.     

Controlling of electronic parameters of GaAs Schottky diode by poly(3,4-ethylenedioxithiophene)-block-poly(ethylene glycol) organic interlayer

The electronic properties of metal-organic semiconductor-inorganic semiconductor structure between GaAs and poly(3,4-ethylenedioxithiophene)-block-poly(ethylene glycol) organic film have been investigated via current-voltage and capacitance-voltage methods. The Au/PEDOT/n-GaAs contact exhibits a rectification behavior with the barrier height of 0.69 eV and ideality factor value of 3.94. The barrier height of the studied diode (0.67 eV) is lower than that of Ni/n-GaAs/In (0.85 eV) and Au/n-GaAs/In Schottky diodes. The decrease in barrier height of Au/n-GaAs/In Schottky diode is likely to be due to the variation in the space charge region in the GaAs. The obtained results indicate that control of the interfacial potential barrier for metal/n-GaAs diode was achieved using thin interlayer of the poly(3,4-ethylenedioxithiophene)-block-poly(ethylene glycol).     

Effects of PCBM concentration on the electrical properties of the Au/P3HT:PCBM/n-Si (MPS) Schottky barrier diodes

In this study, the gold/poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester/n-type silicon (Au/P3HT:PCBM/n-Si) metal–polymer–semiconductor (MPS) Schottky barrier diodes (SBDs) were investigated in terms of the effects of PCBM concentration on the electrical parameters. The forward and reverse bias current–voltage (I–V) characteristics of the Au/P3HT:PCBM/n-Si MPS SBDs fabricated by using the different P3HT:PCBM mass ratios were studied in the dark, at room temperature. The main electrical parameters, such as ideality factor (n), barrier height (Φ_B0), series resistance (R_s), shunt resistance (R_sh), and density of interface states (N_ss) were determined from I–V characteristics for the different P3HT:PCBM mass ratios (2:1, 6:1 and 10:1) used diodes. The values of n, R_s, Φ_B0, and N_ss were reduced, while the carrier mobility and current were increased, by increasing the PCBM concentration in the P3HT:PCBM organic blend layer. The ideal values of electrical parameters were obtained for 2:1 P3HT:PCBM mass ratio used diode. This shows that the electrical properties of MPS diodes strongly depend on the PCBM concentration of the P3HT:PCBM organic layer. Moreover, increasing the PCBM concentration in P3HT:PCBM organic blend layer improves the quality of the Au/P3HT:PCBM/n-Si (MPS) SBDs which enables the fabrication of high-quality electronic and optoelectronic devices.     

Interface control of conventional n-type silicon/metal by n-channel organic semiconductor

The rectifying and interface state density properties of n-Si/violanthrone-79/Au metal-diode have been investigated by current-voltage and capacitance-conductance-frequency methods. The ideality factor, barrier height and average series resistance of the diode were found to be 2.07, 0.81 eV and 5.04 kΩ respectively. At higher voltages, the organic layer contributes to I-V characteristics of the diode due to space-charge injection into the organic semiconductor layer and the trapped-charge-limited current mechanism is dominant mechanism for the diode. The barrier height obtained from C-V measurement is lower than the barrier height obtained I-V measurement and the organic layer creates an excess physical barrier for the diode. The interface state density of the diode was found to be 1.70 × 10¹¹ eV⁻¹ cm⁻² at 0.2 V and 1.72 × 10¹¹ eV⁻¹ cm⁻² at 0.4 V.The obtained electronic parameters indicate that the organic layer provides the conventional n-type silicon/metal interface control option.     

The stability of electrical characteristics of Ti/n-Si/Ag,Ti/n-Si/Cu and Ti/n-Si/AgCu diodes prepared under the same conditions with respect to increasing aging time

The purpose of this study is to fabricate Ti/n-Si/Ag, Ti/n-Si/Cu and Ti/n-Si/AgCu Schottky type diodes and to investigate the effects of aging time on the diode parameters such as ideality factor, barrier height, series resistance, interface state density and rectification ratio. High purity titanium (Ti) metal was deposited on the back side of the n-Si semiconductor and then the Ti/n-Si junction was annealed at 420 °C in nitrogen atmosphere. This junction showed ohmic behavior. To fabricate rectifier contacts, Ag, Cu metals and AgCu alloy have been evaporated on the other polished surface of n-Si with Ti ohmic contact. Ag and Cu ratios in the AgCu alloy which are used in the process of preparing the Schottky contact were taken in equal weights. Thus, Ti/n-Si/Ag, Ti/n-Si/Cu and Ti/n-Si/AgCu Schottky type diodes were prepared under the same conditions. The current-voltage (I-V) characterization of Ti/n-Si/Ag, Ti/n-Si/Cu and Ti/n-Si/AgCu diodes were immediately made at room temperature in dark conditions. To investigate the effect of aging time, the I-V measurements of the diodes have been repeated after 1, 7, 15, 30 and 90 days. Characteristic parameters of the diode were calculated from the I-V measurements which are taken with respect to aging time. The results were compared. From these results, it can clearly be seen that the electrical characteristics of diode which is made from AgCu alloy are more stable than other two diodes.     

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.     

Electrical and photovoltaic properties of a n-Si/chitosan/Ag photodiode

The electrical and photovoltaic properties of AuSb/n-Si/chitosan/Ag diode have been investigated. The ideality factor, barrier height and Richardson constant values of the diode at room temperature were found to be 1.91, 0.88 eV and 121.4 A/cm² K², respectively. The ideality factor of the diode is higher than unity, suggesting that the diode shows a non-ideal behaviour due to series resistance and barrier height inhomogeneities. The barrier height and ideality factor values of Ag/CHT/n-Si diode at room temperature are significantly larger than that of the conventional Ag/n-Si Schottky diode. The φ_B value obtained from C-V measurement is higher than that of φ_B value obtained from I-V measurement. The discrepancy between φ_B(C-V) and φ_B(I-V) barrier height values can be explained by Schottky barrier height inhomogeneities. AuSb/n-Si/chitosan/Ag diode indicates a photovoltaic behaviour with open circuit voltage (V_oc = 0.23 V) and short-circuit current density (J_sc = 0.10 μA/cm⁻²) values.     

The effect of series resistance on calculation of the interface state density distribution in Schottky diodes

This work presents an attempt related to the importance of the fact that the series resistance value is considered in calculating the inter-face state density distribution from the non-ideal forward bias current–voltage (I-V) characteristics of Au/n-Si Schottky barrier diodes (SBDs). To examine the consistency of this approach, Au/n-Si SBDs with Si bulk thicknesses of 200 and 400μm have been prepared. Both diodes showed non-ideal I-V behaviour with ideality factors of 1.14 and 1.12, respectively, and thus it has been thought that the diodes have a metal–interface layer–semiconductor configuration. At the same energy position near the bottom of the conduction band, the interface state density (N _SS) values, without taking into account the series resistance value of the devices, are almost one order of magnitude larger than the N _SS values obtained taking into account the series resistance value.     

Barrier height and ideality factor dependency on identically produced small Au/p-Si Schottky barrier diodes

Small high-quality Au/P-Si Schottky barrier diodes (SBDs) with an extremely low reverse leakage current using wet lithography were produced. Their effective barrier heights (BHs) and ideality factors from current-voltage (Ⅰ-Ⅴ) characteristics were measured by a conducting probe atomic force microscope (C-AFM). In spite of the identical preparation of the diodes there was a diode-to-diode variation in ideality factor and barrier height parameters. By ex-trapolating the plots the built in potential of the Au/p-Si contact was obtained as Vbi = 0.5425 V and the barrier height value φB(C-V) was calculated to be φB(C-V) = 0.7145 V for Au/p-Si. It is found that for the diodes with diameters smaller than 100 μm, the diode barrier height and ideality factor dependency to their diameters and correlation between the diode barrier height and its ideality factor are nonlinear, where similar to the earlier reported different metal semi-conductor diodes in the literature, these parameters for the here manufactured diodes with diameters more than 100μm are also linear. Based on the very obvious sub-nanometer C-AFM produced pictures the scientific evidence behind this controversy is also explained.     

Electrical analysis of organic dye-based MIS Schottky contacts

In this work, we prepared metal/interlayer/semiconductor (MIS) diodes by coating of an organic film on p-Si substrate. Metal(Al)/interlayer(Orange GOG)/semiconductor(p-Si) MIS structure had a good rectifying behavior. By using the forward-bias I-V characteristics, the values of ideality factor (n) and barrier height (BH) for the Al/OG/p-Si MIS diode were obtained as 1.73 and 0.77 eV, respectively. It was seen that the BH value of 0.77 eV calculated for the Al/OG/p-Si MIS diode was significantly larger than the value of 0.50 eV of conventional Al/p-Si Schottky diodes. Modification of the potential barrier of Al/p-Si diode was achieved by using thin interlayer of the OG organic material. This was attributed to the fact that the OG organic interlayer increased the effective barrier height by influencing the space charge region of Si. The interface-state density of the MIS diode was found to vary from 2.79 × 10¹³ to 5.80 × 10¹² eV⁻¹ cm⁻².     

Electrical characterization of current conduction in Au/TiO2/n-Si at wide temperature range

In this study, we have examined Au/TiO₂/n-Si Schottky barrier diodes (SBDs), in order to interpret in detail the experimental observed non-ideal current–voltage–temperature (I–V–T) characteristics. I–V characteristics were measured in the wide temperature range of 80–400 K. TiO₂ was deposited on n-Si substrate by reactive magnetron sputtering. The zero-bias barrier height (ϕ_B0) and ideality factor (n) show strong temperature dependence. While n decreases, ϕ_B0 increases with increasing temperature. Experimental results show that the current across the SBDs may be greatly influenced by the existence of Schottky barrier height (SBH) inhomogeneity. These temperature behaviors have been explained on the basis of the thermionic emission (TE) theory with Gaussian distribution (GD) of the barrier heights (BHs) due to BH inhomogeneities at metal–semiconductor (M/S) interface. From this assumptions, obtaining Richardson constant value of the A^* 121.01 A/cm² K² is perfect agreement with the theoretical value of 120 A/cm² K² for n-type Si. Hence, behaviors of the forward-bias I–V characteristics of the Au/TiO₂/n-Si (SBDs) can be successfully explained on the basis of a TE mechanism with a double Gaussian distribution of the BHs.     

A detailed comparative study on the main electrical parameters of Au/n-Si and Au/PVA:Zn/n-Si Schottky barrier diodes

We have fabricated Au/n-Si and Au/PVA:Zn/n-Si Schottky barrier diodes (SBDs) to investigate the effect of organic interfacial layer on the main electrical characteristics. Zn doped poly(vinyl alcohol) (PVA:Zn) was successfully deposited on n-Si substrate by using the electrospinning system and surface morphology of PVA:Zn was presented by SEM images. The current–voltage (I–V) characteristics of these SBDs have been investigated at room temperature. The experimental results show that interfacial layer enhances the device performance in terms of ideality factor (n), zero-bias barrier height (Φ_B0), series resistance (R_s), and shunt resistance (R_sh) with values of 1.38, 0.75 eV, 97.64 Ω, and 203 MΩ whereas those of Au/n-Si SBD are found as 1.65, 0.62 eV, 164.15 Ω and 0.597 MΩ, respectively. Also, this interfacial layer at metal/semiconductor (M/S) interface leads to a decrease in the magnitude of leakage current and density of interface states (N_ss). The values of N_ss range from 1.36×10¹² at E_c—0.569 eV to 1.35×10¹³ eV^?1 cm^?2 at E_c—0.387 eV for Au/PVA:Zn/n-Si SBD and 3.34×10¹² at E_c—0.560 eV to 1.35×10¹³ eV^?1 cm^?2 at E_c—0.424 eV for Au/n-Si SBD. The analysis of experimental results reveals that the existence of PVA:Zn interfacial layer improves the performance of such devices.     

Electrical and interface state density properties of the 4H-nSiC/[6,6]-phenyl C61-butyric acid methyl ester/Au diode

The electrical and interface state density properties of the Ni/4H-nSiC/PCBM/Au diode have been investigated by current-voltage, capacitance-voltage and conductance-frequency methods. The ideality factor, barrier height and series resistance values of the diode were found to be 2.28, 1.10 eV and 3.76 × 10⁴ Ω, respectively. The diode shows a non-ideal I-V behaviour with an ideality factor greater than unity that could be ascribed to the interfacial layer, interface states and series resistance. The obtained barrier height (1.10 eV) of the Ni/4H-nSiC/PCBM/Au diode is lower than that of Ni/4H-nSiC diode (1.32 eV). This indicates that the PCBM organic layer induces a change of 160 meV in the barrier height of the Ni/4H-nSiC diode. The interface state density of the diode was determined from G_p/ω-f plots and was of order of 5.61 × 10¹² eV⁻¹ cm⁻².     

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.     

ZnO/p-Si heterojunction photodiode by sol–gel deposition of nanostructure n-ZnO film on p-Si substrate

The electrical and photovoltaic properties of the nanostructure ZnO/p-Si diode have been investigated. The nanostructure ZnO/p-Si diode was fabricated using sol–gel spin coating method. The ideality factor and barrier height of the diode were found to be 3.18 and 0.78 eV, respectively. The obtained n ideality factor is higher than 2, indicating that the diode exhibits a non-ideal behavior due to the oxide layer and the presence of surface states. The nanostructure of the ZnO improves the quality of ZnO/p-Si interface. The diode shows a photovoltaic behavior with a maximum open circuit voltage V_oc of 0.26 V and short-circuits current I_sc of 1.87×10^?8 A under 100 mW/cm². It is evaluated that the nanostructure ZnO/p-Si diode is a photodiode with the obtained electronic parameters.     

Current transport mechanisms and deep level transient spectroscopy of Au/n-Si Schottky barrier diodes

The temperature-dependent electrical characteristics of the Au/n-Si Schottky diodes have been studied in the temperature range of 40-300 K. Current density-voltage (J-V) characteristics of these diodes have been analyzed on the basis of thermionic emission theory with Gaussian distribution model of barrier height. The basic diode parameters such as rectification ratio, ideality factor and barrier height were extracted. Under a reverse bias, the conduction process at low voltage is determined by Schottky emission over a potential barrier but at higher voltage the Poole Frenkel effect is observed. The capacitance-voltage (C-V) features of the Au/n-Si Schottky diodes were characterized in the high frequency of 1 MHz. The barrier heights values obtained from the J-V and C-V characteristics have been compared. It has been seen that the barrier height value obtained from the C-V measurements is higher than that obtained from the J-V measurements at various temperatures. Possible explanations for this discrepancy are presented. Deep level transient spectroscopy (DLTS) has been used to investigate deep levels in Au/n-Si. Three electron trap centers, having different emission rates and activation energies, have been observed. It is argued that the origin of these defects is of intrinsic nature. A correlation between C-V and DLTS measurements is investigated.     

The current-voltage-temperature characteristics of Al/NPB/p-Si contact

The current-voltage (I-V) characteristics of the Al/NPB/p-Si contact shows rectifying behavior with a potential barrier formed at the contact interface. The barrier height and ideality factor values of 0.65 eV and 1.33 are measured at the forward bias of the diode. The barrier height of the Al/NPB/p-Si diode at room temperature is larger that (∼0.58 eV) of conventional Al/p-Si diode. It reveals the NPB organic film control the carrier transport of the diode at the contact interface. The temperature effect on the I-V measurement is also performed to reveal the junction characteristics. The ideality factor of the Al/NPB/p-Si contact increases with decreasing temperature. And the barrier height decreases with decreasing temperature. The effects are due to the existence of the interface states and the inhomogeneous of the barrier at the junction.     

Controlling the electrical characteristics of Au/n-Si structures by interfacial insulator layer

Admittance (C–V and G/ω–V) measurements of Au/n-Si (metal–semiconductor, MS) and Au/SnO₂/n-Si (metal–insulator–semiconductor, MIS) structures were carried out between 1 kHz and 1 MHz at room temperature to investigate the interfacial insulator layer effect on the electrical characteristics of Au/n-Si structures. Experimental results showed that MIS structure's capacitance (C) values, unlike those of MS structure, became stable especially at high frequencies in the accumulation region. Also, the insulator layer caused structure's shunt resistance (R_sh) to increase. It was found that series resistance (R_s) is more effective in the accumulation region at high frequencies after the correction was applied to C and G/ω data to eliminate the R_s effect. The density of interface states (D_is) was obtained using Hill–Coleman method, D_is values MIS structure was obtained smaller than those of MS structure. Results indicate that interfacial insulator layer brings about some improvements in electrical characteristics of Au/n-Si structures.     

Electrical and interface properties of Au/DNA/n-Si organic-on-inorganic structures

The effect of the thickness and coverage rate of a DNA film on the electrical and interface properties of Au/DNA/n-Si organic-on-inorganic structures has been investigated. The thin film properties of the DNA deposited on n-Si wafer were characterized by atomic force microscopy. The effect of the thickness and coverage rate of the DNA layer was investigated by evaluating electrical parameters, such as the barrier height, ideality factor, series resistance, and interface state density. The thickness and coverage rate of the DNA layer significantly affects the electrical properties of the Au/DNA/n-Si organic-on-inorganic structures. The interface state density properties of the Au/DNA/n-Si diodes were determined by conductance technique. The results show that the interface state density decreases with decrease in both film thickness and coverage rate of the DNA in an acetate buffer, modifying the electronic parameters of the Au/DNA/n-Si diodes.     

Environmental sensitivity of Au diodes on n-AlGaN

With growing interest in AlGaN for ultraviolet detectors and high-power/high-temperature electronic devices, the problem of forming high-quality Schottky contacts to this semiconductor has become increasingly important. It was shown that wet-chemical surface pretreatments affect the as-deposited diode characteristics for Au/n-AlGaN Schottky diodes. However, these diodes improve over the course of days when exposed to air at room temperature, exhibiting reduced leakage currents, enhanced barrier heights, and reduced ideality factors. Exposure to oxygen, with an enhanced effect in the presence of water vapor, is responsible for the environmental aging. The environmental aging was found to occur regardless of the source of AlGaN, surface preparation, and metal deposition technique. It was determined that high asdeposited reverse currents were due to current transport beneath the contact area, rather than across the semiconductor surface. Two findings further suggested that the change in electrical characteristics was due to a phenomenon occurring at the metal/semiconductor interface. First, metal thickness played a key role in the rate of change of the electrical characteristics, with thicker contacts being more impervious to surrounding gas species at room temperature. Second, a metal that readily forms an oxide, Ni, exhibited little environmental aging, while noble metals, such as Au and Pt, showed dramatic effects. Mild anneals revealed that the environmental change was partially reversible, which suggests the passivation of electrically active defects at the metal/semiconductor interface as the cause of the altered diode behavior. Taken together, the data indicate that oxidizing species diffuse through noble metal contacts to the metal/semiconductor interface and passivate electrically active defects, which may be reactivated upon mild anneals in N₂.