Correlation between barrier heights and ideality factors of Cd/n-Si and Cd/p-Si Schottky barrier diodes

Our goal is to experimentally investigate whether or not the effective Schottky barrier heights (SBHs) and ideality factors obtained from the current-voltage (I-V) and capacitance-voltage (C-V) characteristics differ from diode to diode even if the samples were identically prepared. For this purpose, we prepared Cd/n-Si (33 dots) and Cd/p-Si (15 dots) diodes. The SBH for the Cd/n-Si diodes ranged from 0.701 to 0.605 eV, and ideality factor n from 1.913 to 1.213. Φ_b value for the Cd/p-Si diodes ranged from 0.688 to 0.730 eV, and ideality factor n value from 1.473 to 1.040. The experimental SBH distributions obtained from the C⁻²-V and I-V characteristics were fitted by a Gaussian function and their mean SBH values were calculated. Furthermore, the laterally homogeneous barrier heights were also computed from the extrapolation of the linear plot of experimental barrier heights versus ideality factors.     

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

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

Electronic and interface state density distribution properties of Ag/p-Si Schottky diode

Electronic and interface state distribution properties of Ag/p-Si Schottky diode have been investigated. The diode indicates non-ideal current-voltage behavior with an ideality factor greater than unity. The capacitance-voltage (C-V) characteristic is linear in reverse bias indicating rectification behavior and charge density within depletion layer is uniform. From I-V and C-V characteristics, junction parameters such as diode ideality factor and barrier height were found as 1.66 and ?_B(I-V) = 0.84 eV (?_B(C-V) = 0.90 eV), respectively. The interface state density N_ss and relaxation time τ of the Schottky diode were determined by means of Schottky capacitance spectroscopy method. The results show the presence of thin interfacial layer between the metal and semiconductor.     

Temperature dependent electrical characteristics of Sn/p-Si Schottky diodes

Current-voltage and capacitance-voltage characteristics of Sn/p-Si Schottky diodes measured in the temperature range 80-320 K are presented and analysed. Anomalous strong temperature dependencies of the ideality factor and apparent barrier height were obtained. There was also a considerable difference between the apparent barrier heights obtained from current-voltage and capacitance-voltage characteristics. These anomalies are explained by the domination of the current by a high level of thermionic-field emission, and by the presence of deep levels near the Sn/Si interface, which yield a reduction of free hole concentration and a significant temperature dependence of the charge stored near the metal-semiconductor (MS) interface. The evaluation of temperature dependence of forward current for thermionic-field emission resulted in the following parameters: characteristic energy E₀₀ = 9.8 meV, Schottky barrier height at zero bias Φ_b0 = 0.802 eV, bias coefficient of barrier height β = 0, and effective Richardson constant A* = 37.32 A cm⁻² K⁻².     

Current transport mechanism in Al/Si3N4/p-Si (MIS) Schottky barrier diodes at low temperatures

The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of metal-insulator-semiconductor (Al/Si₃N₄/p-Si) Schottky barrier diodes (SBDs) were measured in the temperature range of 80-300 K. By using the thermionic emission (TE) theory, the zero-bias barrier height Φ_B0 calculated from I-V characteristics was found to increase with increasing temperature. Such temperature dependence is an obvious disagreement with the negative temperature coefficient of the barrier height calculated from C-V characteristics. Also, the ideality factor decreases with increasing temperature, and especially the activation energy plot is nonlinear at low temperatures. Such behaviour is attributed to Schottky barrier inhomogeneties by assuming a Gaussian distribution of barrier heights (BHs) at interface. We attempted to draw a Φ_B0 versus q/2kT plot to obtain evidence of a Gaussian distribution of the BHs, and the values of Φ_Bo = 0.826 eV and α_o = 0.091 V for the mean barrier height and standard deviation at zero-bias, respectively, have been obtained from this plot. Thus, a modified ln(I_o/T²) − q²σ_o²/2(kT)² versus q/kT plot gives Φ_B0 and Richardson constant A^* as 0.820 eV and 30.273 A/cm² K², respectively, without using the temperature coefficient of the barrier height. This value of the Richardson constant 30.273 A/cm² K² is very close to the theoretical value of 32 A/cm² K² for p-type Si. Hence, it has been concluded that the temperature dependence of the forward I-V characteristics of the Al/Si₃N₄/p-Si Schottky barrier diodes can be successfully explained on the basis of TE mechanism with a Gaussian distribution of the barrier heights. In addition, the temperature dependence of energy distribution of interface state density (N_SS) profiles was determined from the forward I-V measurements by taking into account the bias dependence of the effective barrier height and ideality factor.     

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

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

Current conduction mechanism in Al/p-Si Schottky barrier diodes with native insulator layer at low temperatures

The forward bias current-voltage (I-V) characteristics of Al/p-Si (MS) Schottky diodes with native insulator layer were measured in the temperature range of 80-300 K. The obtained zero bias barrier height Φ_B0(I-V), ideality factor (n) and series resistance (R_s) determined by using thermionic emission (TE) mechanism show strong temperature dependence. There is a linear correlation between the Φ_B0(I-V) and n because of the inhomogeneties in the barrier heights (BHs). Calculated values from temperature dependent I-V data reveal an unusual behaviour such that the Φ_B0 decreases, as the n and R_s values are increasing with decreasing absolute temperature, and these changes are more pronounced especially at low temperatures. Such temperature dependence of BH is contradictory with the reported negative temperature coefficient of the barrier height. In order to explain this behaviour we have reported a modification in the expression reverse saturation current I_o including the n and the tunnelling factor (αΧ^1/2δ) estimated to be 15.5. Therefore, corrected effective barrier height Φ_bef.(I-V) versus temperature has a negative temperature coefficients (α = −2.66 × 10⁻⁴ eV/K) and it is in good agreement with negative temperature coefficients (α = −4.73 × 10⁻⁴ eV/K) of Si band gap. In addition, the temperature dependent energy distribution of interface states density N_ss profiles was obtained from the forward bias I-V measurements by taking into account the bias dependence of the Φ_e and n. The forward bias I-V characteristics confirm that the distribution of N_ss, R_s and interfacial insulator layer are important parameters that the current conduction mechanism of MS Schottky diodes.     

Temperature dependence of the current-voltage characteristics of the Al/Rhodamine-101/p-Si(1 0 0) contacts

The current-voltage (I-V) characteristics of Al/Rhodamine-101/p-Si/Al contacts have been measured at temperatures ranging from 280 to 400 K at 20 K intervals. A barrier height (BH) value of 0.817 eV for the Al/Rh101/p-Si/Al contact was obtained at the room temperature that is significantly larger than the value of 0.58 eV of the conventional Al/p-Si Schottky diode. While the barrier height Φ_b0 decreases the ideality factors (n) become larger with lowering temperature. The high values of n depending on the sample temperature may be ascribed to decrease of the exponentially increase rate in current due to space-charge injection into Rh101 thin film at higher voltage. Therefore, at all temperatures, it has been seen that the I-V characteristics show three different regions, the ohmic behavior at low voltages, and the space charge limited current with an exponential distribution of traps at high voltages.     

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

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

Laterally inhomogeneous barrier analysis of the methyl violet/p-Si organic/inorganic hybrid Schottky structures

In this work, we have investigated the electrical characteristics, such as current-voltage (I-V) and capacitance-voltage (C-V) measurements, of identically prepared crystal violet/p-Si Organic/Inorganic (OI) Schottky structures formed by evaporation of organic compound solution to directly p-Si semiconductor substrate. It has been seen that the crystal violet organic dye thin film on the p-Si substrate has exhibited a good rectifying behavior. The barrier heights (BHs) and ideality factors of all devices have been calculated from the electrical characteristics. Although the diodes were all identically prepared, there was a diode-to-diode variation: the effective barrier heights ranged from 0.6 ± 0.1 to 0.8 ± 0.1 eV, and the ideality factor from 1.6 ± 0.4 to 3.5 ± 0.4. The barrier height versus ideality factor plot has been plotted for the OI devices. Lateral homogeneous BH was calculated as a value of 0.7 eV from the observed linear correlation between BH and ideality factor, which can be explained by laterally inhomogeneities of BHs. The values of barrier height and acceptor doping concentration yielded from the reverse bias C-V measurements ranged from 0.7 ± 0.1 to 1.3 ± 0.1 eV and from (4.7 ± 0.8) × 10¹⁴ to (8.1 ± 0.8) × 10¹⁴ cm⁻³, respectively. The mean barrier height and mean acceptor doping concentration from C-V characteristics has been calculated 1.0 eV and 5.9 × 10¹⁴ cm⁻³, respectively. It has been seen that the mean BH value of 0.7 eV obtained for the Al/methyl violet/p-Si contact is significantly larger than BH values of the conventional Al/p-Si Schottky diodes. Thus, modification of the interfacial potential barrier for metal/Si diodes has been achieved using a thin interlayer of the methyl violet organic semiconductor; this has been ascribed to the fact that the methyl violet interlayer increases the effective barrier height by influencing the space charge region of Si.     

Studying of barrier height and ideality factor relation in the nano sized Au-n type Si Schottky diodes

The results of formation of the operating potential barrier height (Φ_в) of inhomogeneous Schottky diodes (SD) in view of an additional electric field in the near contact region of the semiconductor and features of its dependence on the external applied voltage are presented. A correlation, between SD heterogeneity and dependence between potential barrier height (Φ_в) and ideality factor (n), is presented. Using conducting probe atomic force microscope (CP-AFM) techniques, it is shown that Au/n-Si diodes consist of sets of parallel-connected and cooperating nano diodes with the contact surfaces sizes in the order of 100-200 nm. The effective Φ_в and ideality factors of the SD have been obtained from the current-voltage (I-V) characteristics, which were measured using a CP-AFM along a contact surface. It was experimentally shown that the forward and reverse part of I-V characteristics and their effective Φ_в and ideality factors of the identically fabricated nano-SD differ from diode to diode. The Φ_в for the nano-SD has ranged from 0.565 to 0.723 eV and ideality factor from 1.11 to 1.98. No correlation can be found between the Φ_в and ideality factor. The Φ_в distribution obtained from the I-V characteristics has been fitted by a Gaussian function but the ideality factor distribution could not be fitted by a Gaussian function.     

Electrical characterization of p-ZnO/p-Si heterojunction

Nitrogen doped p-ZnO film, with urea as nitrogen source, is fabricated by pulsed laser deposition on well-cleaned p-type (1 0 0) Si substrates. The structural and electrical properties of the p-p heterojunction are investigated by current-voltage (I-V) and capacitance-voltage (C-V) measurements. It shows a diode-like behavior with turn-on voltage of 0.5 V. The ideality factor η determined by applying positive potential in p-ZnO and negative potential along p-Si is found to be 6. Such a high value of η is attributed to lattice mismatch between ZnO and Si. and other factors responsible are thermoionic emission, minority carrier injection and recombination. C-V results indicate an abrupt interface and a band bending of 0.9 V in the silicon. Heterojunction band diagram for p-ZnO/p-Si is proposed.     

Forward and reverse bias current-voltage characteristics of Au/n-Si Schottky barrier diodes with and without SnO2 insulator layer

The effects of interfacial insulator layer, interface states (N_ss) and series resistance (R_s) on the electrical characteristics of Au/n-Si structures have been investigated using forward and reverse bias current-voltage (I-V) characteristics at room temperature. Therefore, Au/n-Si Schottky barrier diodes (SBDs) were fabricated as SBDs with and without insulator SnO₂ layer to explain the effect of insulator layer on main electrical parameters. The values of ideality factor (n), R_s and barrier height (Φ_Bo) were calculated from ln(I) vs. V plots and Cheung methods. The energy density distribution profile of the interface states was obtained from the forward bias I-V data by taking bias dependence of ideality factor, effective barrier height (Φ_e) and R_s into account for MS and MIS SBDs. It was found that N_ss values increase from at about mid-gap energy of Si to bottom of conductance band edge of both SBDs and the MIS SBD’s N_ss values are 5-10 times lower than those of MS SBD’s. An apparent exponential increase from the mid-gap towards the bottom of conductance band is observed for both SBDs’ (MS and MIS) interface states obtained without taking R_s into account.     

The barrier height inhomogeneity in Al/p-Si Schottky barrier diodes with native insulator layer

The current-voltage (I-V) characteristics of Al/p-Si Schottky barrier diodes (SBDs) with native insulator layer were measured in the temperature range of 150-375 K. The estimated zero-bias barrier height Φ_B0 and the ideality factor n assuming thermionic emission (TE) theory show strong temperature dependence. Evaluation of the forward I-V data reveals an increase of zero-bias barrier height Φ_B0 but decrease of ideality factor n with increase in temperature. The conventional Richardson plot exhibits non-linearity below 250 K with the linear portion corresponding to activation energy of 0.41 eV and Richardson constant (A^*) value of 1.3 × 10⁻⁴ A cm⁻² K⁻² is determined from intercept at the ordinate of this experimental plot, which is much lower than the known value of 32 A cm² K² for holes in p-type Si. Such behavior is attributed to Schottky barrier inhomogene ties by assuming a Gaussian distribution of barrier heights (BHs) due to barrier height inhomogeneities that prevail at interface. Also, Φ_B0 versus q/2kT plot was drawn to obtain evidence of a Gaussian distribution of the BHs, and values of Φ_B0 = 1.055 eV and σ₀ = 0.13 V for the mean BH and zero-bias standard deviation have been obtained from this plot, respectively. Thus, the modified versus q/kT plot gives Φ_B0 and A^* as 1.050 eV and 40.08 A cm⁻² K⁻², respectively, without using the temperature coefficient of the barrier height. This value of the Richardson constant 40.03 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 dependence of barrier height on temperature for Pd Schottky contacts on ZnO

Temperature dependent current-voltage (I-V) and capacitance-voltage (C-V) measurements have been performed on Pd/ZnO Schottky barrier diodes in the range 60-300 K. The room temperature values for the zero bias barrier height from the I-V measurements (Φ_I-V) was found to be 0.52 eV and from the C-V measurements (Φ_C-V) as 3.83 eV. From the temperature dependence of forward bias I-V, the barrier height was observed to increase with temperature, a trend that disagrees with the negative temperature coefficient for semiconductor material. The C-V barrier height decreases with temperature, a trend that is in agreement with the negative temperature coefficient of semiconductor material. This has enabled us to fit two curves in two regions (60-120 K and 140-300 K). We have attributed this behaviour to a defect observed by DLTS with energy level 0.31 eV below the conduction band and defect concentration of between 4×10¹⁶ and 6×10¹⁶ cm⁻³ that traps carriers, influencing the determination of the barrier height.     

Effect of series resistance and interface states on the I-V, C-V and G/ω-V characteristics in Au/Bi-doped polyvinyl alcohol (PVA)/n-Si Schottky barrier diodes at room temperature

The forward and reverse bias current-voltage (I-V), capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of the Au/PVA (Bi-doped)/n-Si Schottky barrier diodes (SBDs) have been investigated at room temperature by taking the interface states (N_ss) and series resistance (R_s) effects into account. The voltage dependent profiles of resistance (R_i) were obtained from both the I-V and C/G-V measurements by using Ohm’s Law and Nicollian methods. The obtained values of R_i with agreement each other especially at sufficiently high bias voltages which correspond the value of R_s of the diode. Therefore, the energy density distribution profile of N_ss was obtained from the forward bias I-V data taking the bias dependence of the effective barrier height (BH) Φ_e and R_s into account. The high value of ideality factor (n) was attributed to high density of N_ss and interfacial polymer layer at metal/semiconductor (M/S) interface. In order to examine the frequency dependence of some of the electrical parameters such as doping donor concentration (N_D), Φ_e, R_s and N_ss values, C-V and G/ω-V measurements of the diode were performed at room temperature in the frequency range of 50 kHz-5 MHz. Experimental results confirmed that the N_ss, R_s and interfacial layer are important parameters that influence electrical characteristics of SBD.     

Fabrication and electrical characterization of Au/p-Si/STO/Au contact

Au/STO/p-Si/Au structure is fabricated using pulsed laser deposition technique at room temperature. The current–voltage (I–V) characteristics of the device show rectification behavior. Various junction parameters such as ideality factor, barrier height and series resistance is determined using conventional forward bias I–V characteristics, Cheung method and Norde’s function. Au/STO/p-Si/Au structure shows non-ideal diode characteristics with the value of ideality factor of ∼5.1 and barrier height of ∼0.40 eV.     

Effects of chemical treatment on barrier height and ideality factors of Au/GaN Schottky diodes

We have studied Au/n-GaN Schottky barrier diodes. GaN surfaces have been prepared by cleaning in HCl and (NH₄)₂S prior to metal deposition. The zero-biased barrier heights and ideality factors obtained from the current-voltage characteristics differ from diode to diode, although all the samples were prepared identically. The statistical analysis for the reverse bias C-V data yielded mean value of (1.35±0.04) eV for Schottky barrier height of HCl treated sample and (1.20±0.03) eV for (NH₄)₂S sample, where 9 dots were considered from each cleaning method. It was found that the barrier height values obtained from the C⁻²-V (1.43 eV) and I-V characteristics (0.89 eV) are different from each other by 0.54 eV. The inhomogeneous barrier heights were found to be related to the effect of the high series resistance on diode parameters (Akkiliç et al., 2004) [1].     

Temperature dependence of current-voltage characteristics of Sn/p-Si Schottky contacts

The current-voltage (I-V) characteristics of Sn/p-Si Schottky barrier diode have been measured over a wide range of temperature (80-300 K) and interpreted on the basis of thermionic emission mechanism by merging the concept of barrier inhomogeneities through a Gaussian distribution function. The analysis has revealed an anomalous decrease of apparent barrier height Φ_b0, increase of ideality factor n, and nonlinearity of the activation energy plot at lower temperatures. A Φ_b0 versus 1/T plot has been drawn to obtain evidence of a Gaussian distribution of barrier heights, and values of 0.97 eV and 0.084 V for the mean barrier height and standard deviation σ₀ have been obtained, respectively, from this plot. A modified ln(I₀/T²)−(q²σ₀²/2k²T²) versus 1/T plot gives and Richardson constant A** as 0.95 eV and 15.6 A cm⁻² K⁻², respectively. It can be concluded that the temperature dependent I-V characteristics of the Sn/p-Si Schottky barrier diode can be successfully explained on the basis of a thermionic emission mechanism with Gaussian distribution of the barrier heights. We have also discussed whether or not the junction current has been connected with thermionic field-emission mechanism.     

The effect of series resistance on capacitance-voltage characteristics of Schottky barrier diodes

The capacitance-voltage (C-V) and current-voltage (I-V) characteristics of the Ti/p-Si Schottky barrier diodes (SBDs) have been investigated taking into account the effect of the interface states and series resistance of the device. The forward C-V measurements have been carried out in the range frequency of 0.3-2 MHz (at six different frequencies). It is seen that the forward C-V plots exhibit anomalous peaks in the presence of a series resistance. It has been experimentally determined that the peak positions in the C-V plot shift towards lower voltages and the peak value of the capacitance decreases with increasing frequency. In addition to, the effect of series resistance on the capacitance is found appreciable at higher frequencies due to the capacitance decreases with increasing frequency.