Electrical characteristics of an organic thin copolymer/p-Si Schottky barrier diode

We have fabricated a poly(aniline-3-methyl thiophene) organic thin material on p-Si substrate by placing a solution of copolymer in acetonitrile on top of a p-Si substrate and then evaporating the solvent. The electrical and interface state density properties of the poly(aniline-3-methyl thiophene) copolymer/p-Si/Al diode have been investigated through methods using current-voltage (I-V), Cheung's, and a modified Norde's function. Good agreement was observed with the values of barrier height as obtained from all of these methods. The diode shows a non-ideal I-V behavior with an ideality factor greater than unity, which could be ascribed to the interfacial layer, interface states and series resistance. The interface state density of diode was determined using the forward-bias I-V characteristic technique at room temperature, and it decreases exponentially with bias from 1.39 × 10¹⁶ cm⁻² eV⁻¹ in (0.06 − E_v) eV to 4.86 × 10¹⁵ cm⁻² eV⁻¹ in (0.51 − E_v) eV.     

Effects of oxygen pressure on n-ZnO/p-Si heterojunctions fabricated using pulsed laser deposition

ZnO films were prepared on p-Si substrates using pulsed laser deposition (PLD) and n-ZnO/p-Si heterojunctions were fabricated at different oxygen partial pressures. The effects of oxygen pressures on crystallinity and surface morphology of ZnO films and the I-V characteristics of n-ZnO/p-Si heterojunctions were studied. It was found that the films grown in the oxygen pressure range from 10⁻⁵-10⁻² Torr were all c-axis oriented. The surface morphologies were strongly dependent on the oxygen partial pressure. The current-voltage (I-V) characteristics of the heterojunctions could be classified into two categories depending on the oxygen pressure. At low pressure (10⁻⁵-10⁻⁴ Torr), the I-V curves were similar to those of common p-n junctions. As the oxygen pressure increased to 10⁻³ Torr, the I-V curves changed markedly. Based on the I-V characteristics, an energy band diagram of n-ZnO/p-Si was proposed.     

The determination of interface state energy distribution of the H-terminated Zn/p-type Si Schottky diodes with high series resistance by the admittance spectroscopy

Analysis of Zn/p-Si Schottky diodes (SDs) with high resistivity has been given by admittance spectroscopy. The importance of the series resistance in the determination of energy distribution of interface states and especially their relaxation time in the SDs with high resistivity has been considered. The effect of the series resistance on capacitance-conductance/frequency characteristics has been given by comparing experimental data with theoretical data. The interface state density N_ss from the admittance spectroscopy ranges from 1.0×10¹² cm⁻² eV⁻¹ in 0.720-E_v eV to 2.03×10¹² cm⁻² eV⁻¹ in 0.420-E_v eV. Furthermore, the relaxation time ranges from 4.20×10⁻⁵ s in (0.420-E_v) eV to 3.20×10⁻⁴ s in (0.720-E_v) eV. It has been seen that the interface state density has a very small distribution range (1.0-2.03×10¹² cm⁻² eV⁻¹) that is ascribed to the predominant termination with hydrogen of the silicon surface after HF treatment.     

Analysis of surface states and series resistance in Au/n-Si Schottky diodes with insulator layer using current-voltage and admittance-voltage characteristics

In order to good interpret the experimentally observed Au/n-Si (metal-semiconductor) Schottky diodes with thin insulator layer (18 Å) parameters such as the zero-bias barrier height (Φ_bo), ideality factor (n), series resistance (R_s) and surface states have been investigated using current-voltage (I-V), capacitance-frequency (C-f) and conductance-frequency (G-f) techniques. The forward and reverse bias I-V characteristics of Au/n-Si (MS) Schottky diode were measured at room temperature. In addition, C-f and G-f characteristics were measured in the frequency range of 1 kHz-1 MHz. The higher values of C and G at low frequencies were attributed to the insulator layer and surface states. Under intermediate forward bias, the semi-logarithmic Ln (I)-V plot shows a good linear region. From this region, the slope and the intercept of this plot on the current axis allow to determine the ideality factor (n), the zero-barrier height (Φ_bo) and the saturation current (I_S) evaluated to 2.878, 0.652 and 3.61 × 10⁻⁷ A, respectively. The diode shows non-ideal I-V behavior with ideality factor greater than unity. This behavior can be attributed to the interfacial insulator layer, the surface states, series resistance and the formation barrier inhomogeneity at metal-semiconductor interface. From the C-f and G-f characteristics, the energy distribution of surface states (N_ss) and their relaxation time (τ) have been determined in the energy range of (E_c − 0.493E_v)-(E_c − 0.610) eV taking into account the forward bias I-V data. The values of N_ss and τ change from 9.35 × 10¹³ eV⁻¹ cm⁻² to 2.73 × 10¹³ eV⁻¹ cm⁻² and 1.75 × 10⁻⁵ s to 4.50 × 10⁻⁴ s, respectively.     

Electrical characteristics of Au/n-GaAs Schottky barrier diodes with and without SiO2 insulator layer at room temperature

In this study, our main goal is fabricated with and without insulator layer Au/n-GaAs Schottky barrier diodes (SBDs) to explain whether or not the insulator layer is effective on some electric parameters such as Φ_B, n, N_ss, and R_s. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of metal-semiconductor (Au/n-GaAs) are investigated and compared with metal-insulator-semiconductor (Au/SiO₂/n-GaAs) Schottky diodes. From the room temperature I-V characteristics of these devices, the main electrical parameters such as, ideality factor (n) and zero bias barrier height (Φ_bo) values of 1.25 and 0.73 eV for Au/n-GaAs, and 1.51 and 0.75 eV for Au/SiO₂/n-GaAs, were obtained. The interface distribution profile (N_ss) as a function of (E_c − E_ss) was extracted from the forward-bias I-V measurements by taking into account the bias dependence of the effective barrier height (Φ_e) and series resistance (R_s) for the Schottky diodes. The N_ss values obtained taking into account the series resistance values are lower than those obtained without considering the series resistance. The diodes show non-ideal I-V behavior with ideality factor greater than unity. This behavior is attributed to the interfacial insulator layer and the interface states. The I-V characteristics confirmed that the distribution of N_ss, R_s, and interfacial insulator layer are important parameters that influence the electrical characteristics of metal-semiconductor and metal-insulator-semiconductor Schottky diodes.     

The effect of high temperature annealing on Schottky diode characteristics of Au/n-Si contacts

The current-voltage and capacitance-voltage characteristics of Au/n-Si/Al Schottky barrier diode were measured in the temperature range of 100-800 °C. Au/n-Si/Al Schottky barrier diode annealed at temperatures from 100 °C to 400 °C for 5 min and from 500 °C to 800 °C for 7 min in N₂ atmosphere. The electronic parameters such as barrier height and ideality factor (n) of the device were determined using Cheung's method. To determine whether or not a Schottky diode is ideal it can be used the ideality factor (n) found from its forward current-voltage (I-V) characteristics. It has been found that the value of Φ_b (0.82 or 0.83 eV) remains constant up to 500 °C and 0.80 and 0.79 eV in 600, 750 °C respectively in the forward I-V mode. An ideality factor value of 1.04 was obtained for as-deposited sample. The ideality factor n varied from 1.04 to 2.30. The experimental results have shown that the ideality factor (n) values increases with increasing annealing temperature up to 750 °C. This has been explained in terms of the presence of different metallic-like phases produced by chemical reactions between the Au and Si substrate because of the annealing process. The Φ_b (C-V) values obtained from the reverse-bias C⁻²-V curves of the as-deposited and annealed diode are in the range 0.99-1.12 eV. The difference between Φ_b (C-V) and the Φ_b (I-V) is in close agreement with values reported in literature. Besides Fermi energy level and carrier concentration determined by using thermionic emission (TE) mechanism show strong temperature dependence. It has been seen current-voltage characteristics of the diode show an ideal behavior.     

Capacitance and conductance-frequency characteristics of Au-Sb/p-GaSe:Gd Schottky barrier diode

The Schottky barrier height (SBH) values have been obtained from the reverse bias capacitance-voltage (C-V) characteristics of Au-Sb/p-GaSe:Gd Schottky barrier diode (SBD) in the temperature range of 180-320 K. The forward bias capacitance-frequency (C-f) and conductance-frequency (G-f) measurements of Au-Sb/p-GaSe:Gd SBD have been carried out from 0 to 1.00 V with steps of 0.05 V, whereby the energy distribution of the interface states and their relaxation time have been determined from these characteristics. It has been seen that there is a good agreement between the experimental and theoretical C-f and G-f values. Also, the capacitance values obtained from C-f measurements have shown almost a plateau up to a certain value of frequency, then, have decreased. It has been seen that the interface state density has a very small density distribution range (6.02 × 10¹⁰-6.80 × 10¹⁰ cm⁻² eV⁻¹) in the energy range of (0.21−E_v)-(1.21−E_v) eV with bias from the midgap towards the top of the valence band. The interface state density values calculated for Au-Sb/p-GaSe:Gd SBD are rather low than those given in the literature.     

Influence of tetramethylammonium hydroxide treatment on the electrical characteristics of Ni/Au/GaN Schottky barrier diode

The effect of tetramethylammonium hydroxide (TMAH) treatment on the electrical properties of Ni/Au/GaN Schottky diodes have been investigated by current–voltage (I–V) and capacitance–voltage (C–V) techniques. The barrier heights and ideality factors measured from I–V characteristics are found to be 0.70 eV and 1.32 for without TMAH treatment, and 0.78 eV and 1.14 for with TMAH treatment, respectively. Cheung method is used to measure the series resistance and barrier height of the Schottky diodes, and the barrier height consistency is checked using the Norde method. The magnitude of interface state density for the diodes without and with TMAH treatment are varied from 7.45 × 10¹³ eV⁻¹ cm⁻² to 6.09 × 10¹² eV⁻¹ cm⁻² and 4.03 × 10¹³ eV⁻¹ cm⁻² to 1.79 × 10¹² eV⁻¹ cm⁻² in the below the conduction band from E_C-0.19 eV to E_C-0.63 eV and E_C-0.22 eV to E_C-0.73 eV. Based on the results, the TMAH treatment effectively removes of surface oxide (Ga_xO_y) layer, formed due to the incorporation of the residual oxygen with Ga atom at the GaN surface during the plasma etching. The decrease in interface state density at the Ni/Au/GaN interface could be the reason for the improvement in the electrical properties.     

Antiferromagnetic manganite La1/3Ca2/3MnO3 as barrier material in superconductor/insulator/ferromagnet tunnel junctions

Current transport through thin antiferromagnetic (AF) barriers of the perovskita manganite La_1/3Ca_2/3MnO₃ (LCMO) was studied with respect to its dependence on temperature and voltage. Planar-type La_2/3Ca_1/3MnO₃(~ 80 nm)/La_1/3Ca_2/3MnO₃(~ 7 nm)/YBa₂Cu₃O_7 − δ(~ 100 nm) heterojunctions were used as basic structures. The current-voltage (I-V) measurements were carried out on test junctions with a standard area of 20 × 40 µm² in a four-terminal configuration. In spite of the carefully controlled growth conditions, barriers with the same nominal thickness showed different electrical behavior varying from elastic tunneling to Mott variable range hopping (VRH) via localized states. The different transport characteristics seem to be related to intrinsic difference in microstructure as the average surface roughness of the constituent layers may already be larger than the thickness of the barrier itself.     

Dominant conduction mechanism and the effects of device temperature on electrical characteristics of Al/ZnPc/n-Si structures

Aluminum/Zinc Phthalocyanine/n-Si metal semiconductor contact with organic interfacial layer has been developed and characterized by Current-Voltage-Temperature (I-V-T) measurements for the study of its junction and charge transport properties. The junction parameters, such as diode ideality factor (n), barrier height (φ_b) and series resistance (R_S), of the device were found to shift with device temperature. The diode ideality factor was found to increase with the device temperature up to 323 K. However, a decreasing trend in the value of n was observed beyond this temperature. The barrier height and series resistance were found to increase and decrease, respectively with increasing device temperature. The peak of interface state energy distribution curves was shifted, in terms of Ess-Ev value, from 0.622 eV to 0.827 eV with 52 meV activation energy of the charge carriers. The data analysis implies that the Fermi level of the organic interfacial layer shifts as function of device temperature. In terms of dominant conduction mechanism, the I-V-T data analysis confirms the relationship log (IV⁴) ∝V^1/2 with the device temperature in the range of 313-343 K and the Poole-Frenkel type is found to be the dominant conduction mechanism for the hybrid device.     

High frequency characteristics of tin oxide thin films on Si

High frequency characteristics of tin oxide (SnO₂) thin films were studied. SnO₂ thin films have been successfully grown on n-type Si (111) substrates by using a spray deposition technique. The capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of the metal-oxide-semiconductor (Au/SnO₂/n-Si) Schottky diodes were investigated in the high frequency range from 300 kHz to 5 MHz. It has been shown that the interface state density, D_it, ranges from 2.44 × 10¹³ cm⁻² eV⁻¹ at 300 kHz to 0.57 × 10¹³ cm⁻² eV⁻¹ at 5 MHz and exponentially decreases with increasing frequency. The C-V and G/ω-V characteristics confirm that the interface state density and series resistance of the diode are important parameters that strongly influence the electrical parameters exhibited by the metal-oxide-semiconductor structure.     

Properties of PEDOT:PEG/ZnO/p-Si heterojunction diode

The zinc oxide (ZnO) and poly(3,4-ethylenedioxythiophene) bis-poly(ethyleneglycol) (PEDOT:PEG) films were deposited on p-Si substrate by sputter and spin coating methods, respectively. An organic/inorganic heterojunction diode having PEDOT:PEG/ZnO on p-Si substrate was fabricated. The barrier height (BH) and the ideality factor values for the device were found to be 0.82 ± 0.01 eV and 1.9 ± 0.01, respectively. It has been seen that the value of BH is significantly larger than those of conventional Au/p-Si metal–semiconductor contacts. The PEDOT:PEG/ZnO/p-Si heterostructure exhibits a non-ideal I–V behavior with the ideality factor greater than unity that could be ascribed to the interfacial layer, interface states and series resistance. The modified Norde's function combined with conventional forward I–V method was used to extract the parameters including the barrier height and series resistance. At the same time, the physical properties of ZnO and PEDOT:PEG films deposited by sputter and spin coating technique, respectively, were investigated at room temperature. The obtained results indicate that the electrical parameters of the diode are affected by structural properties of ZnO film and PEDOT:PEG organic film.     

The electrical measurements in poly(2-chloroaniline) based thin film sandwich devices

Al/P2ClAn(CH₃COOH)/p-Si/Al structure has been obtained by evaporation of the polymer P2ClAn(CH₃COOH) on the front surface of p-type silicon substrate, P2ClAn: the poly(2-chloroaniline). The P2ClAn emeraldine salt was chemically synthesized by using acetic acid (CH₃COOH). It has been seen that the current-voltage characteristics of the heterojunction obey to space charge-limited current model. Furthermore, P2ClAn(CH₃COOH) was characterized by using Fourier Transform Infrared (FTIR) and Ultraviolet-Visible (UV-Vis) spectroscopies. An average value of μ, 2.43 × 10^− 5 cm² V^− 1 s^− 1, was obtained for the mobility of the P2ClAn(CH₃COOH); this value is in agreement with the value of about 10^− 4 cm² V^− 1 s^− 1 given for the conjugated polymeric thin films in the literature. Low capacitance-voltage-frequency and conductance-frequency measurements have been made at the voltages of 0.00, 0.02 and 0.30 V in the frequency range of 100 Hz-2.0 MHz. An average value of 7.91 × 10¹¹ cm^− 2 eV^− 1 for interface state density has been obtained from the frequency-capacitance characteristics.     

Photovoltaic and interface state density properties of the Au/n-GaAs Schottky barrier solar cell

The electrical and photovoltaic properties of the Au/n-GaAs Schottky barrier diode have been investigated. From the current-voltage characteristics, the electrical parameters such as, ideality factor and barrier height of the Au/n-GaAs diode were obtained to be 1.95 and 0.86 eV, respectively. The interface state distribution profile of the diode as a function of the bias voltage was extracted from the capacitance-voltage measurements. The interface state density D_it of the diode was found to vary from 3.0 × 10¹¹ eV⁻¹ cm⁻² at 0 V to 4.26 × 10¹⁰ eV⁻¹cm⁻² at 0.5 V. The diode shows a non-ideal current-voltage behavior with the ideality factor higher than unity due to the interfacial insulator layer and interface states. The diode under light illumination exhibits a good photovoltaic behavior. This behavior was explained in terms of minority carrier injection phenomenon. The photovoltaic parameters, such as open circuit voltage and short circuit current density were obtained to be 362 mV and J_sc = 28.3 μA/cm² under AM1, respectively.     

Rectifying pyronine-B/p-type silicon junctions formed by sublimation of pyronine-B

The rectifying junction characteristics of the organic compound pyronine-B film on a p-type Si substrate have been studied. The pyronine-B has been sublimed onto the top of p-Si surface. The barrier height and ideality factor values of 0.79 eV and 1.125 for this structure have been obtained from the forward-bias current–voltage characteristics. The density distribution of the interface states in the inorganic semiconductor bandgap and their relaxation time have been determined from the low-capacitance–frequency characteristics by the Schottky capacitance spectroscopy method. The measurement frequency varies from 90 Hz to 10 MHz. The interface state density N_ss ranges from 2.10×10¹⁰ cm^–2 eV^–1 in (0.79–E_v) eV to 1.16×10¹² cm^–2 eV^–1 in (0.53–E_v) eV. Furthermore, the relaxation time ranges from 1.38×10^–3 s in (0.53–F_V) eV to 7.50×10^–3 s in (0.79–E_V) eV.     

Electrical characterization of the polyaniline/p-silicon and polyaniline titanium dioxide tetradecyltrimethylammonium bromide /p-silicon heterojunctions

Au/PANI/p-Si/Al and Au/PANI TiO₂ TTAB/p-Si/Al heterojunctions have been fabricated by spin coating of soluble polyaniline (PANI) and PANI titanium dioxide (TiO₂) tetradecyltrimethylammonium bromide (TTAB) on the chemically cleaned p-Si substrates. The thicknesses of the polymeric films have been determined by a profilometer. The current-voltage (I-V) characteristics of the heterojunctions have been obtained in the temperature range of 98-258 K. These devices have showed the rectifying behavior such as diode. The I-V characteristics of the devices have been analyzed on the basis of the standard thermionic emission theory at low forward bias voltage regime. It has been shown that the values of ideality factor decrease while the values of barrier height increase with increasing temperature. This temperature dependence has been attributed to the presence of barrier inhomogeneities at the organic/inorganic semiconductor interface. Furthermore, analysis of the double logarithmic I-V plots at higher forward bias voltages at all temperatures indicates that transport through the organic thin film is explained by a space-charge-limited current process characterized by exponential distribution of traps within the band gap of the organic film. The total concentration of traps has been found to be 3.52 × 10¹⁴ cm^− 3 and 3.14 × 10¹⁵ cm^− 3 for PANI and PANI TiO₂ TTAB layer, respectively.     

Impurity induced band-gap narrowing in p-type CuIn1 − xGax(S,Se)2

Green's functions modelling of the impurity induced effects in p-type CuIn_1 − xGa_xS₂ and CuIn_1 − xGa_xSe₂ (x = 0.0, 0.5, and 1.0) reveals that: (i) the critical active acceptor concentration for the metal non-metal transition occurs at N_c ≈ 10¹⁷-10¹⁸ cm^− 3 for impurities with ionization energy of E_A ≈ 30-60 meV. (ii) For acceptor concentrations N_A > N_c, the hole gas of the metallic phase affects the band-edge energies and narrows the energy gap E_g = E_g⁰ − ΔE_g. The energy shift of the valence-band maximum ΔE_v1 is roughly twice as large as the shift of the conduction-band minimum ΔE_c1. (iii) ΔE_v1 depends strongly on the non-parabolicity of the valence bands. (iv) Sulfur based compounds and Ga-rich alloys have the largest shifts of their band edges. (v) A high active acceptor concentrations of N_A = 10²⁰ cm^− 3 implies a band-gap narrowing in the order of ΔE_g ≈ 0.2 eV, thus E_g = E_g⁰ − 0.2 eV, and an optical band gap of E_g^opt ≈ E_g⁰ − 0.1 eV.     

The analysis of the current–voltage characteristics of the high barrier Au/Anthracene/n-Si MIS devices at low temperatures

The Au/Anthracene/n-Si/Al MIS device was fabricated on the basis of anthracene film covalently bonded to a Si substrate. The MIS device showed Schottky behavior with barrier heights of 0.85 eV and ideality factors of 1.88 at 300 K. The barrier height of the Au/n-Si has increased after deposition of the anthracene layer onto Si. Temperature dependent current–voltage (I–V) measurements were performed on the Au/Anthracene/n-Si/Al MIS diodes in the range 140–300 K. From the temperature dependence of forward bias I–V, the barrier height was observed to increase with temperature. However, the ideality factor decreased with increasing temperature. The values of activation energy (E_a) and Richardson constant (A*) were determined as 0.24 eV and 7.57 × 10⁻⁶ A cm⁻² K⁻² from the slope and the intercept at ordinate of the linear region of Richardson plot, respectively. The increase of the series resistance R_s with the fall of temperature was attributed to lack of free carrier concentration at low temperatures.     

Current-voltage and capacitance-voltage characteristics of polypyrrole/p-InP structure

The polypyrrole/p-InP structure has been made by the electrochemical polymerization of the organic polypyrrole onto the p-InP substrate. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of diode have been determined at room temperature and different frequencies. At each frequency, the measured capacitance decreases with increasing frequency due to a continuous distribution of the interface states in the frequency range 50 kHz-1 MHz. From the I-V characteristics of the polypyrrole/p-InP structure, ideality factor and barrier height (BH) values of 1.68 and 0.59 eV, respectively, were obtained from a forward-bias I-V plot. The diode shows non-ideal I-V behavior with ideality greater than unity. This is attributed to the interfacial layer, the interface states and barrier inhomogeneity of the device. As expected, the C-V curves gave a BH value higher than those derived from I-V measurements. This discrepancy can be explained from the fact that due to the different nature of the C-V and I-V measurement techniques, BHs deduced from them are not always the same.