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.     

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.     

Analysis of interface states and series resistance of Ag/SiO2/n-Si MIS Schottky diode using current-voltage and impedance spectroscopy methods

The electrical characteristics and interface state density properties of Ag/SiO₂/n-Si metal-insulator-semiconductor diode have been analyzed by current-voltage and impedance spectroscopy techniques. The electronic parameters such as barrier height, ideality factor and average series resistance were determined and were found to be 0.62 eV, 1.91 and 975.8 Ω, respectively. The calculated ideality factor shows that Ag/SiO₂/n-Si structure obeys a metal-interfacial layer-semiconductor configuration rather than ideal Schottky barrier diode. The interface state density of the diode is of order of ∼10¹¹ eV⁻¹ cm⁻². The dielectrical relaxation mechanism of the diode is analyzed by Cole-Cole plots, indicating the presence of single relaxation mechanism. It is evaluated that the interfacial oxide layer modifies electrical parameters such as interface state density, series resistance and barrier height of Ag/SiO₂/n-Si diode.     

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.     

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.     

Pentacene/n-Si heterojunction diodes and photovoltaic devices investigated by I-V and C-V measurements

The forward and reverse current density-voltage (J-V) and capacitance-voltage (C-V) characteristics of pentacene/n⁻-silicon heterojunction diodes were investigated to clarify the carrier conduction mechanism at the organic/inorganic heterojunction. Current rectification characteristics of the pentacene/n⁻-Si junctions can be explained by a Schottky diode model with an interfacial layer. The diode parameters such as Schottky barrier height and ideality factor were estimated to be 0.79-1.0 eV and 2.4-2.7, respectively. The C-V analysis suggests that the depletion layer appears selectively in the n⁻-Si layer with a thickness of 1.47 μm from the junction with zero bias and the diffusion potential was estimated at 0.30 eV at the open-circuit condition. The present heterojunction allows the photovoltaic operation with power conversion efficiencies up to 0.044% with a simulated solar light exposure of 100 mW/cm².     

Electrical and photovoltaic properties of an organic-inorganic heterojunction based on a BODIPY dye

An organic-inorganic heterojunction based on a BODIPY dyes has been produced by forming dye thin film on n-Si. The electrical parameters of the structure have been investigated by current-voltage (I-V) and capacitance-voltage (C-V) measurements. The ideality factor, the barrier height and the series resistance values of the diode have been calculated as 2.43, 0.84 eV, and about 1.3 kΩ, respectively. The diode behaves as a non-ideal diode because of the series resistance and interface layer. The barrier height value obtained from I-V measurement has been compared with one from C-V measurement. Moreover, it has been seen that the diode is highly sensitive to the light and the reverse bias current increases about 1 × 10⁴ times at −1 V under 100 mW/cm² and AM1.5 illumination condition. The short photocurrent density (J_sc) and the open circuit voltage (V_oc), the fill factor (FF) and power conversion efficiency (η) have been determined as 3.78 mA/cm², 327 mV, 0.28 and 0.48 %, respectively.     

The effects of 12 MeV electron irradiation on the electrical characteristics of the Au/Aniline blue/p-Si/Al device

An Au/Aniline blue (AB)/p-Si/Al structure has been fabricated and then the effect of electron irradiation (12 MeV electron energy and 5 × 10¹² e⁻ cm⁻² fluence) on the contact parameters of the device has been analysed by using the current-voltage (I-V), capacitance-voltage (C-V), and conductance-voltage (G/w-V) measurements, at room temperature. Since the organic layer creates a physical barrier between the metal and the semiconductor, it has been seen that the AB layer causes an increase in the effective barrier height of the device. Cheung functions, Norde model and conductance method have been used in order to determine the diode parameters. The values of the ideality factor, barrier height and series resistance increased after the electron irradiation. This has been attributed to a decrease in the net ionized dopant concentration that occurred as a result of electron irradiation.     

Schottky barrier height modification in Au/n-type 6H-SiC structures by PbS interfacial layer

We have prepared the Au/PbS/n-6H-SiC Schottky diodes with interface layer and the reference Au/n-6H-SiC/Ni Schottky diodes without interface layer to realize Schottky barrier height (SBH) modification in the Au/SiC Schottky diodes. The BH reduction has been succeeded by the PbS interlayer to modify the effective BH by influencing the space charge region of the SiC. The PbS thin layer on the SiC was formed by the vacuum evaporation. The SBH values of 0.97 and 0.89 eV for the samples with and without the interfacial PbS layer were obtained from the forward bias current-voltage (I-V) characteristics. X-ray diffraction (XRD) study was carried out to determine the structural formation of the PbS on SiC. The reduction of the BH in the Au/PbS/n-6H-SiC Schottky diodes has been attributed to the fact that the interface states have a net positive interface charge in metal/n-type semiconductor contact, and thus the positive space charge Q_sc in the Au/PbS/n-6H-SiC Schottky diodes becomes smaller than if the interface state charges Q_ss were absent. The experimental carrier concentration value of 4.73 × 10¹⁷ cm⁻³ obtained from the forward and reverse bias capacitance-voltage characteristics for the Au/PbS/n-6H-SiC contacts is lower than the value of 5.52 × 10¹⁷ cm⁻³ obtained for the reference diode, and this is an evidence of the reduction of the BH by the modification of the space charge density of the SiC.     

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.     

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).     

Laterally inhomogeneous barrier analysis of identically prepared Cd/CdS/n-Si/Au-Sb structures by SILAR method

In this study, CdS thin films have been deposited on n-Si substrate using a successive ionic layer adsorption and reaction (SILAR) method at room temperature. Structural properties have been investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements. The XRD and SEM investigations show that films are covered well, polycrystalline structure and good crystallinity levels. The Cd/CdS/n-Si/Au-Sb structures (28 dots) have been identically prepared by the SILAR method. The effective barrier heights and ideality factors of these structures have been obtained from forward bias current-voltage (I-V) and reverse bias capacitance voltage (C-V) characteristics. The barrier height (BH) for the Cd/CdS/n-Si/Au-Sb structure calculated from the I-V characteristics have ranged from 0.664 eV to 0.710 eV, and the ideality factor from 1.190 to 1.400. Lateral homogeneous barrier height has been determined approximately 0.719 eV from the experimental linear relationship between BHs and ideality factors. The experimental BH and ideality factor distributions obtained from the I-V characteristics have been fitted by a Gaussian function, and their means of values have been found to be (0.683 ± 0.01) eV and (1.287 ± 0.05), respectively. The barrier height values obtained from the reverse bias C⁻²-V characteristics have ranged from 0.720 eV to 0.865 eV and statistical analysis yields the mean (0.759 ± 0.02) eV. Additionally, a doping concentration obtained from C⁻²-V characteristics has been calculated (8.55 ± 1.62) × 10¹⁴ cm⁻³.     

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.     

The analysis of I-V characteristics of Schottky diodes by thermionic emission with a Gaussian distribution of barrier height

The current-voltage (I-V) characteristics of Al/p-Si Schottky barrier diode (SBD) with native insulator layer were measured in the temperature range of 178-440 K. The estimated zero-bias barrier height Φ_B0 and the ideality factor n assuming thermionic emission (TE) theory have shown strong temperature dependence. Evaluation of the forward I-V data have revealed an increase of zero-bias barrier height Φ_B0 but the decrease of ideality factor n with the increase in temperature. The experimental and theoretical results of the tunneling current parameter E_o against kT/q were plotted to determine predominant current-transport mechanism. But the experimental results were found to be disagreement with the theoretical results of the pure TE, the thermionic-field emission (TFE) and the field emission (FE) theories. The conventional Richardson plot has exhibited non-linearity below 240 K with the linear portion corresponding to the activation energy of 0.085 eV and Richardson constant (A^*) value of 2.48 × 10⁻⁹ A cm⁻² K⁻² which is much lower than the known value of 32 A cm⁻² K⁻² for holes in p-type Si. Such behaviours were attributed to Schottky barrier inhomogeneities by assuming a Gaussian distribution of barrier heights (BHs) due to barrier height inhomogeneities that prevail at interface. Thus, the modified ln(I_o/T²) − q2σo2/2k²T² vs q/kT has plotted. Then A^* was calculated as 38.79 A cm⁻² K⁻² without using the temperature coefficient of the barrier height. This value of the Richardson constant 38.79 A cm⁻² K⁻² is very close to the theoretical value of 32 A K⁻² cm⁻² for p-type Si. Hence, it has been concluded that the temperature dependence of the forward I-V characteristics of the Al/p-Si Schottky barrier diodes with native insulator layer can be successfully explained on the basis of TE mechanism with a Gaussian distribution of the barrier heights.     

The electrical characteristics of Sn/methyl-red/p-type Si/Al contacts

The junction characteristics of the organic compound methyl-red film (2-[4-(dimethylamino)phenylazo]benzoic acid) on a p-type Si substrate have been studied. The current-voltage characteristics of the device have rectifying behavior with a potential barrier formed at the interface. The barrier height and ideality factor values of 0.73 eV and 3.22 for the structure have been obtained from the forward bias current-voltage (I-V) characteristics. The interface state energy distribution and their relaxation time have ranged from 1.68 × 10¹² cm⁻² eV⁻¹ and 1.68 × 10⁻³ s in (0.73-E_v) eV to 1.80 × 10¹² cm⁻² eV⁻¹ and 5.29 × 10⁻⁵ s in (0.43-E_v) eV, respectively, from the forward bias capacitance-frequency and conductance-frequency characteristics. Furthermore, the relaxation time of the interface states shows an exponential rise with bias from (0.43-E_v) eV towards (0.73-E_v) eV.     

Analysis of electronic parameters and interface states of boron dispersed triethanolamine/p-Si structure by AFM, I-V, C-V-f and G/ω-V-f techniques

The electronic parameters and interface state properties of boron dispersed triethanolamine/p-Si structure have been investigated by atomic force microscopy, I-V, C-V-f and G/ω-V-f techniques. The surface topography and phase image of the TEA-B film deposited onto p-Si substrate were analyzed by atomic force microscopy. The atomic force microscopy results show a homogenous distribution of boron particles in triethanolamine film. The electronic parameters (barrier height, ideality factor and average series resistance) obtained from I-V characteristics of the diode are 0.81 eV, 2.07 and 5.04 kΩ, respectively. The interface state density of the diode was found to be 2.54 × 10¹⁰ eV⁻ cm⁻² under V_g = 0. The obtained D_it values obtained from C-V and G/ω measurements are in agreement with each other. The profile of series resistance dependent on voltage and frequency confirms the presence of interface states in boron dispersed triethanolamine/p-Si structure. It is evaluated that the boron dispersed triethanolamine controls the electronic parameters and interface properties of conventional Al/p-Si diode.     

Effect of 6 MeV electron irradiation on electrical characteristics of the Au/n-Si/Al Schottky diode

Electron irradiation of the Au/n-Si/Al Schottky diode was performed by using 6 MeV electrons and 3 × 10¹² e⁻/cm² fluency. The current-voltage (I-V), capacitance-voltage (C-V) and capacitance-frequency (C-f) characteristics of the unirradiated and irradiated Schottky diode were analyzed. It was seen that the values of the barrier height, the series resistance, and the ideality factor increased after electron irradiation. However, there was a decrease in the leakage current with electron irradiation. The increase in the barrier height and in the series resistance values was attributed to the dopant deactivation in the near-interface region. The interface states, N_ss, have been decreased significantly after electron irradiation. This was attributed to the decrease in recombination centre and the existence of an interfacial layer. A decrease in the capacitance was observed after electron irradiation. This was attributed to decrease in the net ionized dopant concentration with electron irradiation.     

Modification of metal/semiconductor junctions by self-assembled monolayer organic films

Two new metal/molecule/semiconductor contacts, Au/n-Si/TDA/Au and Au/p-Si/ODM/Au, were fabricated to understand effect of organic compounds, tridecylamine and octadecylmercaptan self-assembled monolayer (SAM) films, on electrical charge transport properties of the metal/semiconductor junctions. The morphology of the organic monolayers deposited on Si substrates was investigated by atomic force microscopy. The molecular coverage of ODM deposited on p-Si is poorer than that of TDA on n-Si substrate. The ideality factors of the p-Si/ODM and n-Si/TDA diodes were found to be 1.66 and 1.48, respectively. The electrical results show that the tridecylamine monolayer passivated junction has a lower ideality factor. The ideality factor indicates clear dependence on two different type functional groups R-SH (Thiol) and R-NH₂ (Amin) groups and it increases with different functional groups of organic molecule. The barrier height φ_b value of the n-Si/TDA diode is smaller than that of p-Si/ODM diode, as a result of chain length of the SAM organic molecules. The interface state density D_it values of the diodes were determined using conductance technique. The n-Si/TDA diode has the smaller interface state density according to p-Si/ODM diode.We have evaluated that the organic molecules control the electronic parameters of metal/semiconductor diodes and thus, organic modification helps to get one step closer towards to new organic assisted silicon based microelectronic devices.     

Calculation from the current-voltage and capacitance-voltage measurements of characteristics parameters of Cd/CdS/n-Si/Au-Sb structure with CdS interface layer grown on n-Si substrate by SILAR method

The CdS thin film has been directly formed on n-type Si substrate to form an interfacial layer between cadmium (Cd) and n-type Si with Successive Ionic Layer Adsorption and Reaction (SILAR) method. An Au-Sb electrode has been used as an ohmic contact. The Cd/CdS/n-Si/Au-Sb structure has demonstrated clearly rectifying behaviour by the current-voltage (I-V) curves studied at room temperature. The characteristics parameters such as barrier height, ideality factor and series resistance of Cd/CdS/n-Si/Au-Sb structure have been calculated from the forward bias I-V and reverse bias C⁻²-V characteristics. The diode ideality factor and the barrier height have been calculated as n = 2.06 and Φ_b = 0.92 eV by applying a thermionic emission theory, respectively. The diode shows non-ideal I-V behaviour with an ideality factor greater than unity that can be ascribed to the interfacial layer, the interface states and the series resistance. At high current densities in the forward direction, the series resistance (R_s) effect has been observed. The values of R_s obtained from dV/d(lnI)-I and H(I)-I plots are near to each others (R_s = 182.24 Ω and R_s = 186.04 Ω, respectively). This case shows the consistency of the Cheung′s approach. In the same way, the barrier height calculated from C⁻² -V characteristics varied from 0.698 to 0.743 eV. Furthermore, the density distribution of interface states (N_ss) of the device has been obtained from the forward bias I-V characteristics. It has been seen that, the N_ss has almost an exponential rise with bias from the mid gap toward the bottom of conduction band.     

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.