Temperature dependence of the electrical and interface states of the Sn/Rhodamine-101/p-Si Schottky structures

In this paper, the current–voltage (I–V) characteristics of Sn/Rhodamine-101/p-Si/Al contacts have been measured at temperatures ranging from 80 to 400 K at 30 K intervals. The nonpolymeric organic compound Rhodamine-101 (Rh101) film on a p-type Si substrate has been formed by means of the evaporation process and the Sn/Rhodamine-101/Si contacts have been fabricated. The current–voltage characteristics of the diode show rectifying behaviour consistent with a potential barrier formed at the interface. The obtained I–V barrier heights (Φ_b) were in the range of 0.208–0.940 eV with ideality factors (n) of 14.37–2.72. The high values of ideality factor (n) may be ascribed to decrease the exponentially increase rate in current due to space-charge injection into Rh101 thin film at higher voltage. Temperature dependence of the energy distribution of interface states density profile was determined from the forward bias I–V characteristics. It is shown that organic semiconductor layer (Rhodamine-101) controls electrical charge transport properties of Sn/p-Si Schottky structure by excluding effects.     

The effect of a novel organic compound chiral macrocyclic tetraamide-I interfacial layer on the calculation of electrical characteristics of an Al/tetraamide-I/p-Si contact

The Al/tetraamide-I/p-Si Schottky barrier diode (SBD) has been prepared by adding a solution of a novel nonpolymeric organic compound chiral macrocylic tetraamide-I in chloroform on top of a p-Si substrate and then evaporating the solvent. It has been seen that the forward-bias current–voltage (I–V) characteristics of Al/tetraamide-I/p-Si SBD with a barrier height value of 0.75 eV and an ideality factor value of 1.77 showed rectifying behaviour. The energy distribution of the interface state density determined from I–V characteristics increases exponentially with bias from 5.81 × 10¹² cm⁻² eV⁻¹ at (0.59-E_v) eV to 1.02 × 10¹³ cm⁻² eV⁻¹ at (0.40-E_v) eV. It has showed that space charge limited current (SCLC) and trap charge limited current (TCLC) are the dominant transport mechanisms at large forward-bias voltages.     

Electrical and optical properties of p-type silicon based on polypyrrole-derivative polymer

The junction characteristics of the conducting polymer NpClPh PPy [N-(p-chloro phenyl) polypyrrole] on a p-type Si substrate have been studied at room temperature. A direct optical band gap energy value of conducting polymer (NpClPh PPy) was obtained as 2.94 eV. The ideality factor and barrier height of Al/NpClPh PPy/p-Si/Al structure were determined from the forward current–voltage characteristics in the dark and were found to be 1.41 and 0.78 eV, respectively. The ideality factor and barrier height values for the Al/NpClPh PPy/p-Si/Al structure are larger than that of conventional Al/p-Si Schottky diode. The contact parameters were calculated from Cheung's functions and modified Norde's function. The results found out from different methods were compared with each other. The barrier height value of 0.89 eV was obtained from capacitance–voltage characteristic. The different values of barrier height indicate the existence of barrier inhomogeneities. The conducting polymer (NpClPh PPy) modifies the effective barrier height of conventional Al/p-Si Schottky diode as the organic film forms a physical barrier between Al metal and p-Si.     

Extraction of electronic parameters of organic diode fabricated with NIR absorbing functional manganase phthalocyanine organic semiconductor

The semiconducting and metal/organic semiconductor properties of the newly synthesized NIR absorbing α-substituted manganase phthalocyanine bearing functional 2,3-dihydroxypropylthio moieties {M[Pc(S–CH₃CH₂(OH)CH₂(OH))]₄X}(M = Mn^III) have been investigated by electrical conductivity–temperature, optical absorption and current–voltage characteristics methods. The electrical conductivity increases with the temperature, suggesting that the peripheral α-substituted-functional manganase phthalocyanine is an organic semiconductor. The optical band gap and trap energy values were determined and were found to be 2.98 eV and 1.95 eV, respectively. The ITO/MnPc/Al diode shows a rectifying behavior due to the formation of MnPc/Al interface with a rectification ratio of 29.4 at ±2 V. The series resistance R_s and ideality factor n values were found to be 102.6 kΩ and 8.89, respectively. The interface state density for the diode was of order of 2.73 × 10¹¹ eV^?1 cm^?2 with the interface time constant of 1.93 × 10^?5.It is evaluated that newly synthesized α-substituted manganase phthalocyanine bearing functional 2,3-dihydroxypropylthio moieties is an organic semiconductor and can be used in electronic device applications as an organic diode.     

Extraction of the device parameters of Al/P3OT/ITO organic Schottky diode using J–V and C–V characteristics

Thin film of poly(3-octylthiophene) (P₃OT) was successfully prepared using dip coating technique. The morphology and the crystal structure of the prepared thin film were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. A study on interface states density distribution and characteristic parameters of the Al/P₃OT/ITO device capacitor have been made. The diode parameters such as ideality factor, series resistance and barrier height were extracted from the forward biasing J–V characteristics. The energy distribution of the interface state density D_it was determined from the forward bias J–V characteristics by taking into account the bias dependence of the effective barrier height. The C–V and G/ω–V characteristics were measured in the frequency range from 10 kHz to 1 MHz and dc biasing voltage swept from ?4 V to +4 V at room temperature (300 K). The non-ideal behavior of J–V and C–V characteristics can be attributed to the presence of the interface and the series resistance.     

Electrical and photovoltaic properties of FeTPPCl/p-Si heterojunction

Hybrid heterojunction cell based on thermally evaporated 5,10,15,20-tetraphenyl-21H, 23H-porphine iron (III) chloride (FeTPPCl) as the organic semiconductor and p-Si wafer as the inorganic semiconductor have been investigated. This device showed rectification behaviour like diode. The conduction mechanisms and the diode parameters have been studied using current–voltage (I–V) characteristics in the temperature range (298–373 K) and capacitance–voltage (C–V) characteristics at room temperature. This cell exhibited photovoltaic characteristics with a short-circuit current (I_sc) of 2.8 mA, an open-circuit voltage (V_oc) of 0.475 V, a fill factor FF = 32%.     

Modification of electrical properties of the Au/1,1′ dimethyl ferrocenecarboxylate/n-Si Schottky diode

The electrical and interface state density properties of the Au/1,1′ dimethyl ferrocenecarboxylate (DMFC)/n-Si structure have been investigated by current–voltage, capacitance–voltage and conductance–frequency methods. The Au/DMFC/n-Si structure exhibits a rectifying behavior with a non-ideal I–V behavior with an ideality factor greater than unity. The ideality factor and barrier height of the Au/DMFC/n-Si Schottky diode is lower than that of Au/n-Si Schottky diode. The interface state density of the diode was determined from G/ω–f plots and was of order of 5.61 × 10¹² eV^?1 cm^?2. It is evaluated that the electrical properties of Au/n-Si diode is controlled using 1′ dimethyl ferrocenecarboxylate organic layer and in turn, Au/DMFC/n-Si structure gives new electronic parameters.     

Charge transport properties of an organic solar cell

The electronic properties of ITO/PEDOT-PSS/P3HT-PCBM/LiF/Al organic solar cell have been investigated using current-voltage and capacitance-voltage techniques. The electrical parameters like ideality factor n, series resistance R_s and barrier height ?_b, have been extracted using current-voltage and capacitance-voltage techniques. The photovoltaic parameters such as open circuit voltage V_oc, short circuit current I_sc and fill factor FF were determined from current-voltage characteristics of the solar cell under illumination. The ideal value than unity for the organic solar cell indicates the presence of non-ideal behaviour. The barrier height of the solar cell is found to be dependent both temperature and applied voltage and the model of Gaussian distribution of the barrier height was presented for explaining their anomalous behaviour. The standard deviation of the barrier height distribution σ_o indicates the presence of interface inhomogeneities. The ideality factor n, open circuit voltage V_oc, short circuit current density J_sc, fill factor FF and Richardson constant A* values for the organic solar cell were found to be 2.29, 0.58 V, 5.84 mA/cm², 0.31 and 10.41 A/cm² K², respectively.     

Controlling of silicon–insulator–metal junction by organic semiconductor polymer thin film

Electrical and photovoltaic properties of a metal–semiconductor–insulator–polymer–metal diode were investigated. The n-Si/SiO₂/MEH-PPV/Al diode shows a rectifying behavior with the rectification ratio of 2.22 × 10⁵ at ±5 V and exhibits a non-ideal behavior due to the series resistance and oxide-organic layers. The organic semiconductor makes a contribution to the I–V characteristics of the diode and the trap-charge limited space charge and space charge limited current mechanisms were observed for the diode. The current–voltage characteristics of the n-Si/SiO₂/MEH-PPV/Al diode under different illumination intensities give an open circuit voltage (V_oc) along with a short circuit current (I_sc). This suggests that the n-Si/SiO₂/MEH-PPV/Al diode is a photovoltaic device with V_oc = 0.456 V and J_sc = 7.89 × 10^?8 A/cm² values under 100 mW/cm² illumination intensity. The photoconductivity mechanism of the diode is controlled by monomolecular recombination. The interface state density D_it values with time constant τ_it of the diode under dark and illumination conditions were found to be 2.53 × 10¹⁰ eV^?1 cm^?2 with 5.09 × 10^?5 s and 2.50 × 10¹⁰ eV^?1 cm^?2 with 8.27 × 10^?5 s, respectively. The obtained results indicate that the n-Si/SiO₂/MEH-PPV/Al diode is a photo-sensitive diode.     

Current–voltage and capacitance–voltage characteristics of a Sn/Methylene Blue/p-Si Schottky diode

Electrical and interfacial properties of Sn/Methylene Blue (MB)/p-Si Schottky diode have been determined by using current–voltage (I–V) and capacitance–voltage (C–V) measurements of the device at room temperature. Cheung functions and modified Norde functions have been used to obtain the electrical characteristics such as barrier height and series resistance of the diode. It has been seen that the MB layer modifies the effective barrier height of the structure because the layer creates the physical barrier between the metal and the semiconductor. Electrical properties of the device obtained from C–V characteristics have been compared with the ones obtained from its I–V characteristics. It has been seen that at sufficiently high frequencies, the charge at the interface cannot follow an ac signal. The interface state density of the diode has been also calculated.     

Carrier transport properties of aluminum oxide/polypyrrole films doped with naphthalene-1,5-disulfonic acid

The electrical structure of the Al/Al₂O₃/PPy-NDSA/Au has been investigated by means of current–voltage (I–V) and capacitance–voltage (C–V) measurements, in a temperature range of 90–350 K. The forward C–V measurements have been carried out in the range of frequency of 1 kHz to 20 MHz. The effects of series resistance, interfacial layer and interface states on I–V and C–V characteristics are investigated. At high current densities in the forward direction, the series resistance effect has been observed for voltages greater than 0.7 V. The analysis of I–V characteristics based on the thermionic emission mechanism has been explained by the assumption of a Gaussian distribution of barrier heights, due to barrier height inhomogeneities that prevail at the interface. It has been observed that the forward C–V plot exhibits a peak, whose position shifts towards lower voltages and that decreases with increasing frequency. The non-linearity of 1/C² versus V plot at high frequency was explained with the assumption that only some of the interface states follow the applied ac signal. Surface analysis by X-ray photoelectron spectroscopy (XPS) was performed in order to evaluate the chemical states of the constituents of the Al/Al₂O₃/PPy-NDSA/Au sample.     

Rectification and barrier height inhomogeneous in Rhodamine B based organic Schottky diode

Thermogravimetric analysis (TGA) and X-ray diffraction (XRD) were used to study the structure characterization of the Rhodamine B (Rh.B). The thermal stability and the lattice parameters were calculated using TGA and XRD, respectively. Bulk Al/Rh.B Schottky barrier device was prepared and their properties have been investigated by current density–voltage J–V and capacitance–voltage C–V characteristics in the temperature range 300–400 K. The device parameters extracted from the J–V and C–V characteristics are strongly influenced by the effect of temperature. The device exhibits a strong rectification characteristic and shows a maximum rectification ratio at ≈0.15 V for all the studied temperature range. The results clearly demonstrate that the electron transport at the Al/Rh.B interface is significantly affected by low barrier patches. The discrepancy between Schottky barrier heights (SBHs) obtained from the temperature dependencies of both J–V and C–V measurements is explained by the introduction of a spatial distribution of BHs due to the barrier height inhomogeneities that prevail at the Al/Rh.B interface. The deviations of apparent BHs were investigated by considering the microstructure of the Al/Rh.B interface. Moreover, the distribution of carrier concentration through the width of the depletion region is nearly uniform.     

Photovoltaic properties of a single layer poly [3-(4-octylphenyl)-2,2′-bithiophene] (PTOPT)

A Schottky contact is made from a single layer polymer poly [3-(4-octylphenyl)-2,2′-bithiophene] (PTOPT) in its neutral state and a low work function metal (Al). The electrical and optical properties have been investigated by means of I–V measurements in the dark and under illumination. Various parameters such as the reverse saturation current density, barrier height, and diode quality factor were determined from the I–V curves in the dark of Al/PTOPT/ITO sandwich structure using thermionic emission theory. Spectral response of the device was measured at various wavelengths giving a peak at 500 nm. The IPCE% was obtained for illumination through both the Al and ITO sides. By illuminating the diode with a monochromatic light of wavelength 500 nm, the open-circuit voltage, short-circuit current density, power conversion efficiency, and fill-factor (FF) were obtained. The dependence of photocurrent on light intensity was also recorded and analyzed.     

The calculation of electronic parameters of an Ag/chitin/n-Si Schottky barrier diode

We have formed polymeric organic compound chitin film on n-Si substrate by adding a solution of polymeric compound chitin in N,N-dimethylacetamide and lithium chloride on top of an n-Si substrate and then evaporating solvent. It has been seen that the chitin/n-Si contact has demonstrated clearly rectifying behavior and the reverse curves exhibit a weak bias voltage dependence by the current–voltage (I–V) curves studied at room temperature. The barrier height and ideality factor values of 0.959 eV and 1.553, respectively, for this structure have been obtained from the forward bias I–V characteristics. Furthermore, the energy distribution of the interface state density located in the semiconductor band gap at the chitin/n-Si substrate in the energy range from (E_c − 0.897) to (E_c − 0.574) eV have been determined from the I–V characteristics. The interface state density, N_ss, ranges from 5.965 × 10¹² cm⁻² eV⁻¹ in (E_c − 0.897) eV to 1.706 × 10¹³ cm⁻² eV⁻¹ in (E_c − 0.574) eV and has an exponential rise with bias this energy range.     

Current–voltage characteristics of an organic diode: Revisited

For over 40 years the current–voltage (J–V) characteristics of an organic diode with exponentially distributed traps have been interpreted using the equation J ∝ V^m, where m > 2. This equation is based on the classical work of Helfrich and Mark (W. Helfrich, P. Mark, Z. Phys. 168 (1962) 495). It is based on the assumption that the injection barrier is zero. However, the recent results show that in many cases the Schottky barrier is not zero and modification in this equation is necessary. We present a mathematical simulation, taking into account the effect of non-zero Schottky barrier. The experiments show good agreement with the simulated results.     

The current–voltage and capacitance–voltage characteristics of molecularly modified β-carotene/n-type Si junction structure with fluorescein sodium salt

β-Carotene–FSS organic semiconductor/n-type Si structure has been characterized by current–voltage and capacitance–voltage methods. A deviation in I–V characteristic of the diode is observed due to effect of series resistance and interfacial layer. Cheung's functions were used to calculate diode parameters. The ideality factor, series resistance and barrier height values of the diode are n = 1.77, R_s = 10.32 (10.39) kΩ and 0.78 eV. The obtained ideality factor suggests that Au/β-carotene–FSS/n-Si Schottky diode has a metal–SiO₂ oxide layer plus organic layer–semiconductor (MIOS) configuration. The capacitance–voltage characterizations of Au/β-carotene–FSS/n-Si diode at different temperatures were performed. The capacitance of the diode changes with temperature. The barrier height and ideality factor obtained from C–V curves are 0.67 eV and 1.68. The interface density properties of the diode are analyzed and the shape of the density distribution of the interface states is in the range of E_c −0.49 to −0.62 eV. It is evaluated that the FSS organic layer controls electrical charge transport properties of Au/β-carotene/n-Si diode by excluding effects of the β-carotene and SiO₂ residual oxides on the hybrid diode.     

Current–voltage characteristics of Al/Rhodamine-101/n-GaAs and Cu/Rhodamine-101/n-GaAs rectifier contacts

The organic compound Rhodamine-101 (Rh101) film on an n-type GaAs substrate with carrier concentration of 7.3 × 10¹⁵ cm⁻³ has been formed by means of the evaporation process, and thus Al/Rh101/n-GaAs and Cu/Rh101/n-GaAs contacts have been fabricated. Our aim is to realize a modification of Schottky barrier height (SBH) of the devices using a thin non-polymeric organic compound layer. The Al/Rh101/n-GaAs and Cu/Rh101/n-GaAs contacts have behaved like rectifying contact with the SBH values of 0.68 eV and 0.72 eV, and with ideality factor values of 2.61 and 2.60 obtained from their forward bias current–voltage (I–V) characteristics at the room temperature, respectively. It has seen that the SBH values obtained for these devices are significantly different from those obtained for the conventional Al/n-GaAs or Cu/n-GaAs Schottky diodes. Furthermore, it has been demonstrated that the trapped-charge-limited current is the dominant transport mechanism at large forward bias voltage.     

The calculation of electronic properties of an Ag/chitosan/n-Si Schottky barrier diode

In this study, the film of chitosan by adding the solution of chitosan being a polymeric compound on the top of an n-Si substrate and then by evaporating solvent was formed. It was seen that the chitosan/n-Si contact demonstrated clearly rectifying behavior and the reverse curves exhibit a weak bias voltage dependence by the current–voltage (I–V) curves studied at room temperature. Average barrier height and ideality factor values for this structure were determined as 0.94 eV and 1.81, respectively. Furthermore, the energy distribution of the interface state density located in the semiconductor band gap at the chitosan/n-Si substrate in the energy range (E_c−0.785) to (E_c−0.522) eV have been determined from the I–V characteristics. The interface state density N_ss ranges from 5.39 × 10¹² cm⁻² eV⁻¹ in (E_c−0.785) eV to 1.52 × 10¹³ cm⁻² eV⁻¹ in (E_c−0.522) eV. The interface state density has an exponential rise with bias from the midgap towards the bottom of the conduction band.     

The performance improvement in pentacene organic thin film transistors by inserting C60/MoO3 ultrathin layers

A series of bottom-gated top-contact pentacene organic thin film transistors are fabricated. C₆₀ and/or MoO₃ ultrathin layers are inserted between the pentacene and Al source-drain electrodes to reduce the contact resistance. With proper order and thickness of the two layers modification, the injection barrier is greatly lowered down and the field-effect mobility increases from 0.095 cm²/(V s) to 0.65 cm²/(V s). The threshold voltage decreases from ?11.3 V to ?6.4 V. It means that the injection barrier plays an important role in the contact resistance without modification and multiple ultrathin layers modification is an effective method to improve the performance of the OTFTs. Then the output curve of the devices with better modification is simulated by a charge drift model. Taking into account of the contact effect, the field-effect mobility is improved to 1.05 cm²/(V s). It indicates that after modification, the injection barrier is lowered down, but the contact resistance caused by the charge drift in the contact region become the more important role and still affect the performance.     

Kinetics of interface state-limited hole injection in α-naphthylphenylbiphenyl diamine (α-NPD) thin layers

Injection-limited operation is identified in thin-film, α-NPD-based diodes. A detailed model for the impedance of the injection process is provided which considers the kinetics of filling/releasing of interface states as the key factor behind the injection mechanism. The injection model is able to simultaneously account for the steady-state, current–voltage (J–V) characteristics and impedance response, and is based on the sequential injection of holes mediated by energetically distributed surface states at the metal–organic interface. The model takes into account the vacuum level offset caused by the interface dipole, along with the partial shift of the interface level distribution with bias voltage. This approach connects the low-frequency (～1 Hz) capacitance spectra, which exhibits a transition between positive to negative values, to the change in the occupancy of interface states with voltage. Simulations based on the model allow to derive the density of interface states effectively intervening in the carrier injection (～5 × 10¹² cm^?2), which exhibit a Gaussian-like distribution. A kinetically determined hole barrier is calculated at levels located ～0.4 eV below the contact work function.