Analysis of interface states and series resistance of MIS Schottky diodes using the current-voltage (I-V) characteristics

The purpose of this paper is to analyze interface states in Al/SiO₂/p-Si (MIS) Schottky diodes and determine the effect of SiO₂ surface preparation on the interface state energy distribution. The current-voltage (I-V) characteristics of MIS Schottky diodes were measured at room temperature. From the I-V characteristics of the MIS Schottky diode, ideality factor (n) and barrier height (Φ_B) values of 1.537 and 0.763 eV, respectively, were obtained from a forward bias I-V plot. In addition, the density of interface states (N_ss) as a function of (E_ss-E_v) was extracted from the forward bias I-V measurements by taking into account both the bias dependence of the effective barrier height (Φ_e), n and R_s for the MIS Schottky diode. The diode shows non-ideal I-V behaviour with ideality factor greater than unity. In addition, the values of series resistance (R_s) were determined using Cheung’s method. 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 MIS Schottky diodes.     

Ta/Si Schottky diodes fabricated by magnetron sputtering technique

Electrical properties of Ta/n-Si and Ta/p-Si Schottky barrier diodes obtained by sputtering of tantalum (Ta) metal on semiconductors have been investigated. The characteristic parameters of these contacts like barrier height, ideality factor and series resistance have been calculated using current voltage (I-V) measurements. It has seen that the diodes have ideality factors more than unity and the sum of their barrier heights is 1.21 eV which is higher than the band gap of the silicon (1.12 eV). The results have been attributed the effects of inhomogeneities at the interface of the devices and native oxide layer. In addition, the barrier height values determined using capacitance-voltage (C-V) measurements have been compared the ones obtained from I-V measurements. It has seen that the interface states have strong effects on electrical properties of the diodes such as C-V and R_s-V measurements.     

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.     

Extraction of electronic parameters of Schottky diode based on an organic Orcein

An Au/Orcein/p-Si/Al device was fabricated and the current-voltage measurements of the devices showed diode characteristics. Then the current-voltage (I-V), capacitance-voltage (C-V) and capacitance-frequency (C-f) characteristics of the device were investigated at room temperature. Some junction parameters of the device such as ideality factor, barrier height, and series resistance were determined from I-V and C-V characteristics. The ideality factor of 2.48 and barrier height of 0.70 eV were calculated using I-V characteristics. It has been seen that the Orcein layer increases the effective barrier height of the structure since this layer creates the physical barrier between the Au and the p-Si. The interface state density N_ss were determined from the I-V plots. The capacitance measurements were determined as a function of voltage and frequency. It was seen that the values of capacitance have modified with bias and frequency.     

Characterization of current-voltage (I-V) and capacitance-voltage-frequency (C-V-f) features of Al/SiO2/p-Si (MIS) Schottky diodes

The current-voltage (I-V) characteristics of metal-insulator-semiconductor Al/SiO₂/p-Si (MIS) Schottky diodes were measured at room temperature (300 K). In addition, capacitance-voltage-frequency (C-V-f) characteristics are investigated by considering the interface states (N_ss) at frequency range 100 kHz to 1 MHz. The MIS Schottky diode having interfacial insulator layer thickness of 33 Å, calculated from the measurement of the insulator capacitance in the strong accumulation region. At each frequency, the measured capacitance decreases with increasing frequency due to a continuous distribution of the interface states. From the I-V characteristics of the MIS Schottky diode, ideality factor (n) and barrier height (Φ_b) values of 1.766 and 0.786 eV, respectively, were obtained from a forward bias I-V plot. In addition, the interface states 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) for the Schottky diode. The diode shows non-ideal I-V behaviour with ideality factor greater than unity. This behaviour is attributed to the interfacial insulator layer, the interface states and barrier inhomogeneity of the device. As expected, the C-V curves gave a barrier height value higher than those obtained from I-V measurements. This discrepancy is due to the different nature of the I-V and C-V measurement techniques.     

Electrical characteristics and inhomogeneous barrier analysis of Au-Be/p-InSe:Cd Schottky barrier diodes

We have identically prepared Au-Be/p-InSe:Cd Schottky barrier diodes (SBDs) (21 dots) on the InSe:Cd substrate. The electrical analysis of Au-Be/p-InSe:Cd structure has been investigated by means of current-voltage (I-V), capacitance-voltage (C-V) and capacitance-frequency (C-f) measurements at 296 K temperature in dark conditions. The effective barrier heights and ideality factors of identically fabricated Au-Be/p-InSe:Cd SBDs have been calculated from their experimental forward bias current-voltage (I-V) characteristics by applying a thermionic emission theory. The BH values obtained from the I-V characteristics have varied between 0.74 eV and 0.82 eV with values of ideality factors ranging between 1.49 and 1.11 for the Au-Be/p-InSe:Cd SBDs. It has been determined a lateral homogeneous barrier height value of approximately 0.82 eV for these structures from the experimental linear relationship between barrier heights and ideality factors. The Schottky barrier height (SBH) value has been obtained from the reverse-bias C-V characteristics of Au-Be/p-InSe:Cd SBD for only one diode. At high currents in the forward direction, the series resistance effect has been observed. The value of series resistance has been determined from I-V measurements using Cheung’s and Norde’s methods.     

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.     

Temperature-dependent current-voltage characteristics of Cr/n-GaAs Schottky diodes

The Cr/n-GaAs/In Schottky contacts have been formed using dc magnetron sputtering. The current-voltage (I-V) characteristics of the device have been measured by steps of 20 K in the temperature range of 60-320 K. The ideality factor n of the device has remained about unchanged between 1.04 and 1.10 and Schottky barrier height around 0.58-0.60 eV from 320 K down to 160 K. It can be said that the experimental I-V data are almost independent of temperature above 160 K. After 160 K, the n value increased with a decrease in temperature and become 1.99 at 60 K. The I-V characteristics at high temperatures have been exactly explained by the standard TE model. The nature and origin of abnormal behaviors at low temperatures have been successfully explained by the current flow through the low SBH circular patches suggested by Tung and used by some studies in literature. It has been seen that the straight line of the nT vs. T plot with a T₀ value of 14 K was parallel to that of the ideal Schottky contact. Again, a lateral homogeneous BH value of 0.62 eV was calculated from the linear relationship between the ideality factor and barrier height values. It has been seen that he ?(T = 0) and BH temperature coefficient α values obtained from the flat band BH and the Norde’s model plots are in close agreement with each other.     

Electrical characterization of MS and MIS structures on AlGaN/AlN/GaN heterostructures

The forward and reverse bias I-V, C-V, and G/ω-V characteristics of (Ni/Au) Schottky barrier diodes (SBDs) on the Al_0.22Ga_0.78N/AlN/GaN high-electron-mobility-transistor (HEMTs) without and with SiN_x insulator layer were measured at room temperature in order to investigate the effects of the insulator layer (SiN_x) on the main electrical parameters such as the ideality factor (n), zero-bias barrier height (Ф_B0), series resistance (R_s), interface-state density (N_ss). The energy density distribution profiles of the N_ss were obtained from the forward bias I-V characteristics by taking into account the voltage dependence of the effective barrier height (Ф_e) and ideality factor (n_V) of devices. In addition, the N_ss as a function of E_c-E_ss was determined from the low-high frequency capacitance methods. It was found that the values of N_ss and R_s in SBD HEMTs decreases with increasing insulator layer thickness.     

Temperature dependence of barrier height parameters of inhomogeneous Schottky diodes

We have shown by numerical simulations of I-V-T curves that the ideality factor of inhomogeneous Schottky diodes does not increase for decreasing temperature to such extent as is commonly observed for Schottky diodes in experiment. The main consequence of such a result is that in spite of the fact that the barrier height inhomogeneities fullfil the conditions for barrier height lowering for decreasing temperature they might not be a general or the only reason for occuring of this effect in experimental structures. We found out much slower ideality factor temperature dependence than reported in the literature and the dependence was even not monotonous for simulation conditions used. We conclude that some other reason as barrier inhomogeneity is responsible for ideality factor temperature dependence.     

Current-voltage characteristics of p-Si/carbon junctions fabricated by pulsed laser deposition

Amorphous carbon/p-Si junctions were fabricated at different temperatures using KrF excimer laser (λ = 248 nm, pulsed duration 20 ns). The current-voltage measurements of the devices showed diode characteristics. The value of various junction parameters such as ideality factor, barrier height, and series resistance were determined from forward bias I-V characteristics, Cheung method, and Norde’s function. There was a good agreement between the diodes parameters obtained from these methods. The ideality factor of ∼1.12 and barrier height of ∼0.37 eV were estimated using current-voltage characteristics for films grown at room temperature.     

Annealing temperature effect on electrical and structural properties of Cu/Au Schottky contacts to n-type GaN

Schottky contacts were fabricated on n-type GaN using a Cu/Au metallization scheme, and the electrical and structural properties have been investigated as a function of annealing temperature by current-voltage (I-V), capacitance-voltage (C-V), Auger electron spectroscopy (AES) and X-ray diffraction (XRD) measurements. The extracted Schottky barrier height of the as-deposited contact was found to be 0.69 eV (I-V) and 0.77 eV (C-V), respectively. However, the Schottky barrier height of the Cu/Au contact slightly increases to 0.77 eV (I-V) and 1.18 eV (C-V) when the contact was annealed at 300 °C for 1 min. It is shown that the Schottky barrier height decreases to 0.73 eV (I-V) and 0.99 eV (C-V), 0.56 eV (I-V) and 0.87 eV (C-V) after annealing at 400 °C and 500 °C for 1 min in N₂ atmosphere. Norde method was also used to extract the barrier height of Cu/Au contacts and the values are 0.69 eV for the as-deposited, 0.76 eV at 300 °C, 0.71 eV at 400 °C and 0.56 eV at 500 °C which are in good agreement with those obtained by the I-V method. Based on Auger electron spectroscopy and X-ray diffraction results, the formation of nitride phases at the Cu/Au/n-GaN interface could be the reason for the degradation of Schottky barrier height upon annealing at 500 °C.     

The frequency and voltage dependent electrical characteristics of Al-TiW-Pd2Si/n-Si structure using I-V, C-V and G/ω-V measurements

The forward and reverse bias capacitance-voltage (C-V) and conductance-voltage (G/w-V) characteristics of Al-TiW-Pd₂Si/n-Si structures have been investigated over a wide frequency range of 5 kHz-5 MHz. These measurements allow to us the determination of the interface states density (N_ss) and series resistance (R_s) distribution profile. The effect of R_s on C and G is found noticeable at high frequencies. The C-V-f and G/w-V-f characteristics of studied structures show fairly large frequency dispersion especially at low frequencies due to N_ss in equilibrium with the semiconductor. The N_ss profile was obtained both forward bias current-voltage (I-V) characteristics by using into account the bias dependent of the ideality factor and effective barrier height (Φ_e) and low frequency (C_LF)-high frequency (C_HF) method. The plot of series resistance vs. voltage for the low frequencies gives a peak, decreasing with increasing frequencies. The frequency dependent C-V and G/w-V characteristics confirm that the R_s and N_ss of the Al-TiW-Pd₂Si/n-Si structures are important parameters that strongly influence the electric parameters in device.     

Influence of inhomogeneous contact in electrical properties of 4H–SiC based Schottky diode

Schottky diodes realized on 4H–SiC n-type wafers with an epitaxial layer and a metal-oxide overlap for electric field termination were studied. The oxide was grown by plasma enhanced chemical vapor deposition (PECVD) and the Schottky barriers were formed by thermal evaporation of titanium or nickel. Diodes, with voltage breakdown as high as 700 V and ideality factor as low as 1.05, were obtained and characterized after packaging in standard commercial package (TO220).The electrical properties such as ideality factor, hight barrier, the series resistance R_s were deduced by current/voltage (I–V) analysis using the least mean square (LMS) method. The temperature effect on break voltage, R_s and saturation current was studied. A model based on two parallel Schottky diodes with two barrier heights is presented for some devices having an inhomogeneous contact. It is shown that the excess current at low voltage can be explained by a lowering of the Schottky barrier in localized regions. We use the two series RC components electrical model in order to study the dynamic behaviour of the Schottky diode in low frequency and to improve the effect of barrier inhomogeneities in electrical properties.     

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

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

The role of the interface insulator layer and interface states on the current-transport mechanism of Schottky diodes in wide temperature range

In order to interpret in detail the experimentally observed current-voltage-temperature (I-V-T) and capacitance-voltage-temperature (C-V-T) results of Al/p-Si metal-semiconductor Schottky barrier diodes (SBDs) we have been examined the samples in the temperature range of 150-375 K. In the calculation method, to confirm the relationship between the I-V-T and C-V-T results, we have reported a modification which includes the ideality factor, n, and tunnelling parameter δχ^1/2 in the forward bias current characteristics. In the intermediate bias voltage region (0.1 < V < 0.6 V), the semi-logarithmic plots of the forward I-V-T curves were found to be linear. From the reverse saturation currents I₀ obtained by extrapolating the linear region of curves to zero applied voltage, the values of zero bias barrier heights ?_B0 were calculated at each temperature. The values of ideality factor calculated from the slope of each curves were plotted as a function of temperature. The values of n are 3.41-1.40 indicating that the Al/p-Si diode does obey the thermionic field emission (TFE) mechanism rather than the other transport mechanism, particularly at low temperature. The high value of ideality factors is attributed to high density of interface states in the SBDs. The temperature dependence energy density distribution profile of interface state was obtained from the forward bias I-V-T measurements by taking into account the bias dependence of the effective barrier height and ideality factor. The interface states density N_ss decreasing with increasing temperature was interpreted by the result of atomic restructuring and reordering at the metal-semiconductor interface. After the modification was made to the forward current expression, we obtained a good agreement between the values of barrier height obtained from both methods over a wide temperature.     

Electrical characteristics of Pd Schottky contacts on ZnO films

The electrical characteristics of Pd Schottky contacts on ZnO films have been investigated by current-voltage (I–V) and capacitance–voltage (C–V) measurements at different temperatures. ZnO films of two thicknesses (400 nm and 1000 nm) were grown by DC-magnetron sputtering on n-Si substrates. The basic structural, optical and electrical properties of these films are also reported. We compared the two Schottky diodes by means of characteristic parameters, such as rectification ratio, ideality factor (η), barrier height (Φ_b) and series resistance and obtained better results for the 1000 nm-ZnO Schottky diodes. We also discussed the dependence of I‐V characteristics on temperature and the two distinct linear regions observed at low temperatures are attributed to the existence of two different inhomogeneous barrier heights. From I–V plots in a log-log scale we found that the dominant current-transport mechanism at large forward bias is space-charge limited current (SCLC) controlled by the presence of traps within the ZnO bandgap. The existence of such traps (deep states or interface states) is demonstrated by frequency-dependent capacitance and deep-level transient spectroscopy (DLTS) measurements.     

The theoretical and experimental study on double-Gaussian distribution in inhomogeneous barrier-height Schottky contacts

We have considered multi-Gaussian distribution of barrier-heights for non-interactive barrier inhomogeneities in the inhomogeneous Schottky diodes, and we have shown the presence of the intersecting behavior in the forward-bias current-voltage (I-V) curves for the double-Gaussian distribution model at low temperatures. We have tried to eliminate this effect by generating I-V curves at lower temperatures with the bias-dependent barrier-height expression which leads to the ideality factors greater than unity. For this calculation, we have obtained the expressions for the barrier-height change and ideality factor, and for bias-dependency of the BH for the multi-Gaussian model by following the literature. We have shown that the experimental forward-bias I-V curves coincide with the theoretical ones using the bias-dependent inhomogeneous BH expression at low and high temperatures in the double-Gaussian distribution of BHs.     

Characterization of aluminum/LPCVD polysilicon Schottky barrier diodes

The I-V characteristics of aluminum Schottky diodes made on LPCVD deposited polysilicon with a wide range of doping concentration (8.5 × 10¹⁵−1.7 × 10²⁰ cm⁻³) have been investigated. Diodes with ideality factor n = 1.12 at room temperature were obtained with doping concentration ≤ 8.5 × 10¹⁶ cm⁻³. In contrast to large grain polysilicon, uniform I-V characteristics can be obtained across the wafer on fine grain LPCVD polysilicon. A barrier height of qφ_B0.73 eV at 300 K was consistently determined from both the I-V measurements and the specific contact resistance measurements. The contact resistance of aluminum/polysilicon contacts is well described by present theory except in the intermediate doping range.     

Barrier characteristics of gold Schottky contacts on moderately doped n-InP based on temperature dependent I-V and C-V measurements

The temperature dependences of current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the gold Schottky contacts on moderately doped n-InP (Au/MD n-InP) Schottky barrier diodes (SBDs) have been systematically investigated in the temperature range of 60-300 K. The main diode parameters, ideality factor (n) and zero-bias barrier height (apparent barrier height) were found to be strongly temperature dependent and while the decreases, the n and the increase with decreasing temperature. According to Thermionic Emission (TE) theory, the slope of the conventional Richardson plot [In(J₀/T²) vs. 1000/T] should give the barrier height. However, the experimental data obtained do not correlate well with a straight line below 160 K. This behaviour has been interpreted on the basis of standard TE theory and the assumption of a Gaussian distribution of the barrier heights due to barrier inhomogeneities that persist at the metal-semiconductor interface. The linearity of the apparent barrier height vs. 1/(2kT) plot that yields a mean barrier height of 0.526 eV and a standard deviation (σ_s0) of 0.06 eV, was interpreted as an evidence to apply the Gaussian distribution of the barrier height. Furthermore, modified Richardson plot [ vs. 1/T] has a good linearity over the investigated temperature range and gives the and the Richardson constant (A^∗) values as 0.532 eV and 15.90 AK⁻²cm⁻², respectively. The mean barrier heights obtained from both plots are appropriate with each other and the value of A^∗ obtained from the modified Richardson plot is close to the theoretical value of 9.4 AK⁻²cm⁻² for n-InP. From the C-V characteristics, measured at 1 MHz, the capacitance was determined to increase with increasing temperature. C-V measurements have resulted in higher barrier heights than those obtained from I-V measurements. The discrepancy between Schottky barrier heights(SBHs) obtained from I-V and C-V measurements was also interpreted. As a result, it can be concluded that the temperature dependent characteristic parameters for Au/MD n-InP SBDs can be successfully explained on the basis of TE mechanism with Gaussian distribution of the barrier heights.