Dependence Of Barrier Height Research Articles

Extraction of the device parameters of Al/P 3OT/ITO organic Schottky diode using J–V and C–V characteristics

Thin film of poly(3-octylthiophene) (P 3OT) 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/P 3OT/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.

Design and characterization of TlInSe 2 varactor devices

TlInSe 2 single crystal has been successfully prepared by the Bridgman crystal growth technique. The crystal, which exhibits compositional atomic percentages of 25.4%, 25.2% and 49.4% for Tl, In and Se, respectively, is found to be of tetragonal structure with lattice parameters of a=0.8035 and c=0.6883 nm. The crystals were used to design radio frequency sensitive varactor device. The temperature dependence of the current–voltage characteristics of the device allowed the calculation of the room temperature barrier height and ideality factor as 0.87 eV and as 3.2, respectively. Rising the device temperature increased the barrier height and decreased the ideality factor. This behavior was attributed to the current transport across the metal–semiconductor interface. The capacitance of the device is observed to increase with increasing voltage and increasing temperature as well. The temperature activation of the capacitance starts above 82 °C with a temperature coefficient of capacitance being 1.08×10 −3 K −1. Furthermore, the capacitance of the device was observed to increase with increasing frequency up to a maximum critical frequency of 4.0 kHz, after which the capacitance decreased with increasing frequency. The behavior reflected the ability of maximum amount of charge holding being at a 4.0 kHz. The analysis of the capacitance–voltage characteristics at fixed frequencies reflected a frequency dependent barrier height and acceptors density. The decrease in the barrier height and acceptors density with increasing frequency is mainly due to the inability of the free charge to follow the ac signal.

Analysis of the forward and reverse bias I-V characteristics on Au/PVA:Zn/n-Si Schottky barrier diodes in the wide temperature range

In this study, the forward and reverse bias current-voltage (I-V) characteristics of Au/Zinc acetate doped polyvinyl alcohol/n-Si Schottky barrier diodes (SBDs) have been investigated over the temperature range of 80-400 K. The values of zero-bias barrier height evaluated from forward and reverse bias I-V data, (ФBFo) and (ФBRo), increase with increasing temperature, and a discrepancy is observed between the values of ФBFo and ФBRo. Because the apparent barrier height (BH) seen from metal to semiconductor is higher than the one seen from semiconductor to metal, the obtained value of ФBFo is always greater than ФBRo value. The difference between them is almost the same as the Fermi energy level. The crossing of the experimental forward bias semilogarithmic ln I-V plots appears as an abnormality when compared to the conventional behavior of ideal SBDs. This behavior was attributed to the lack of free charge at a low temperature and could be expected in the temperature region where there is no carrier freezing out, which is non-negligible at low temperatures. Prior to intersection, the voltage dependent value of resistance (Ri) obtained from Ohm’s law decreases with increasing temperature, but it begins to increase after this intersection point. Such an increase in ФBo and series resistance (Rs) with temperature corresponding to high voltage region is in obvious disagreement with the reported negative temperature coefficients. However, the value of shunt resistance (Rsh) corresponding to a low or negative voltage region decreases with increasing temperature. In addition, the temperature dependent energy density distribution profiles of interface states (Nss) were obtained from forward bias I-V measurements by taking into account the bias dependence of the effective barrier height (Фe) and Rs of the device, and the values of Nss without considering Rs are almost one order of magnitude larger than Nss when considering Rs value.

Gaussian distribution of Schottky barrier heights on SnO2 nanowires

ABSTRACTIn this work, we studied metal/SnO2 junctions using transport properties. Parameters such as barrier height, ideality factor and series resistance were estimated at different temperatures. Schottky barrier height showed a small deviation of the theoretical value mainly because the barrier was considered fixed as described by ideal thermionic emission-diffusion model. These deviations have been explained by assuming the presence of barrier height inhomogeneities. Such assumption can also explain the high ideality factor as well as the Schottky barrier height and ideality factor dependence on temperature.

Temperature dependence of current-voltage characteristics of Ni–AlGaN/GaN Schottky diodes

Ni–AlGaN/GaN Schottky barrier diodes (SBDs) with lateral geometry were fabricated on sapphire substrates. At 300 K, devices with 500-μm-diameter Schottky contacts exhibited breakdown voltage (VB) of 765 V, forward current (IF) of 0.065 A at 1.5 V, and specific on-resistance (Ron) of 81.3 mΩ cm2, producing a figure-of-merit (VB2/Ron) of ∼7.2 MW cm−2. Measured in multifinger patterns, the same parameters were 420 V, 3.2 A, 4.6 mΩ cm2, and 38.4 MW cm−2, respectively, at 300 K. With the increase in measurement temperature from 300 to 450 K, SBDs with dimensions of 3000×3000 μm2 showed larger effective barrier heights (0.8 eV at 300 K and 1.27 eV at 475 K) and a slightly negative temperature coefficient (−0.48 V K−1) for reverse breakdown voltage, while there was a little change in reverse leakage current. These results show the strong influence of barrier height inhomogeneity on the temperature dependence of apparent barrier heights obtained through current-voltage measurements.

On the energy distribution profile of interface states obtained by taking into account of series resistance in Al/TiO 2/p–Si (MIS) structures

The energy distribution profile of the interface states ( N ss ) of Al/TiO 2/p–Si (MIS) structures prepared using the sol–gel method was obtained from the forward bias current–voltage ( I–V) characteristics by taking into account both the bias dependence of the effective barrier height ( ϕ e ) and series resistance ( R s ) at room temperature. The main electrical parameters of the MIS structure such as ideality factor ( n), zero-bias barrier height ( ϕ b0 ) and average series resistance values were found to be 1.69, 0.519 eV and 659 Ω, respectively. This high value of n was attributed to the presence of an interfacial insulator layer at the Al/p–Si interface and the density of interface states ( N ss ) localized at the Si/TiO 2 interface. The values of N ss localized at the Si/TiO 2 interface were found with and without the R s at 0.25 -E v in the range between 8.4×10 13 and 4.9×10 13 eV −1 cm −2. In addition, the frequency dependence of capacitance–voltage ( C– V) and conductance–voltage ( G/ω– V) characteristics of the structures have been investigated by taking into account the effect of N ss and R s at room temperature. It can be found out that the measured C and G/ω are strongly dependent on bias voltage and frequency.

Effects of oxidation on surface chemical states and barrier height of AlGaN/GaN heterostructures

The effects of oxidation on the surface structure and chemical bonding states of AlGaN/GaN heterostructures were investigated using x-ray photoelectron spectroscopy (XPS). In comparing Al 2p core-level XPS spectra among as-grown and annealed samples, we found that Al atoms on the surface were highly oxidized after rapid thermal annealing (RTA) at high temperature; not only in an O2 but also in an N2 gas atmosphere. The Al oxidation level was almost identical for the samples annealed at 800 °C, irrespective of the annealing atmosphere and time; yet there was a strong dependence on the annealing temperature. The dependence of surface barrier height on the annealing condition is associated with Al oxidation behavior. Before the RTA, the barrier height increased together with the AlGaN thickness, indicating an unpinned Fermi level and the existence of low-density and distributed surface donor states. After the high-temperature RTA, however, the height is maintained at a certain value, regardless of the thickness, due to Fermi level pinning by high-density donor states. These results can be explained by the formation of two types of oxide structures providing different types of donor states.

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.

Photoassisted tunneling from free-standing GaAs thin films into metallic surfaces

The tunnel photocurrent between a gold surface and a free-standing semiconducting thin film excited from the rear by above bandgap light has been measured as a function of applied bias, tunnel distance and excitation light power. The results are compared with the predictions of a model which includes the bias dependence of the tunnel barrier height and the bias-induced decrease of surface recombination velocity. It is found that i) the tunnel photocurrent from the conduction band dominates that from surface states. ii) At large tunnel distance the exponential bias dependence of the current is explained by that of the tunnel barrier height, while at small distance the change of surface recombination velocity is dominant.

Fermi-level pinning and charge neutrality level in nitrogen-doped Ge2Sb2Te5: Characterization and application in phase change memory devices

We study the dependence of the hole barrier height at the metal/α-Ge2Sb2Te5 interface as a function of nitrogen doping in Ge2Sb2Te5 as well as the vacuum work function of the metal. Materials parameters such as the band gap, dielectric constant, and electron affinity values of these nitrogen-doped films were also determined. All Ge2Sb2Te5 films studied in this work are amorphous. Following further physical analysis, the effective work functions of metals on nitrogen-doped Ge2Sb2Te5 films were obtained and found to differ from that of their values in vacuum. This led to the extraction of the slope parameter Sx and charge neutrality level ΦCNL which characterizes Ge2Sb2Te5. Appreciable metal Fermi-level pinning to the charge neutrality level of Ge2Sb2Te5, which is located near the valence band edge, was observed. We then demonstrate application of the extracted parameters to obtain the band alignment of α-Ge2Sb2Te5 with various other materials such as SiO2, giving good agreement with experimental results.

A comparative study on the electrical characteristics of Au/n-Si structures with anatase and rutile phase TiO 2 interfacial insulator layer

TiO 2 thin films were deposited on polycrystalline n-type Si substrate using DC magnetron sputtering system. To improve the crystal quality, thermal annealing (TA) process was done at 700 °C and 900 °C. The effect of TA on the structural properties was investigated using high resolution X-ray diffraction (HRXRD). It was observed that the phase transition from amorphous phase to anatase and rutile phases occurs at 700 °C and 900 °C, respectively. Au/TiO 2/n-Si structures were also fabricated for the investigation of TA on the main electrical parameters, such as ideality factor ( n), barrier height ( Φ B), series resistance ( R s), shunt resistance ( R sh) and interface states ( N ss). The current–voltage ( I– V) and capacitance–voltage ( C– V) characteristics have been investigated at room temperature and results have been compared with each other. The electrical characteristics showed that TA strongly affects the main electrical parameters. The rectifying ratio of Au/n-Si structures with anatase phase TiO 2 was to be 140 while the rutile phase was to be 8864. The leakage current was also found to be very sensitive to the annealing temperature, and also the magnitude of the leakage current for rutile phase is 15 times lower than the anatase phase's. In addition, the energy distribution profile of N ss of the structures was obtained from the forward bias I– V data by taking the bias dependence of the effective barrier height ( Φ e) into account. For both of the samples, the value of N ss decreases with TA. Similarly, the values of R s and R sh of the structures obtained from the forward bias I– V data were found as 209 Ω and 42 kΩ for the anatase and 59 Ω and 598 kΩ for the rutile phase. These results show that the performance of the Au/TiO 2/n-Si structure improved with thermal annealing.

Electrical characteristics of DNA-based metal-insulator-semiconductor structures

High quality sandwich device was fabricated from wheat DNA molecular film by solution processing located between Au and n-type silicon inorganic semiconductor. We have performed the electrical characteristics of the device such as current–voltage (I–V) and capacitance–voltage (C–V) at room temperature. DNA-based on this structure showed an excellent rectifying behavior with a typical ideality factor of 1.22, and that DNA film increased the effective barrier height by influencing the space charge region of Si. We proposed that DNA could be an insulatorlike material with a wide optical band energy gap of 4.19 eV from its optical absorbance characteristics. Additionally, the energy distribution of interface state density, determined from the forward bias I–V characteristics by taking into account the bias dependence of the effective barrier height, decreases exponentially with bias from 7.48×1015 m−2 eV−1 in (Ec−0.40) eV to 8.56×1014 m−2 eV−1 in (Ec−0.72) eV.

The interface states and series resistance effects on the forward and reverse bias I– V, C– V and G/ ω- V characteristics of Al–TiW–Pd 2Si/ n-Si Schottky barrier diodes

Illumination intensity effects on the electrical characteristics of Al–TiW–Pd 2Si/ n-Si Schottky structures have been investigated in this study for the first time. The electrical parameters such as ideality factor ( n), zero-bias-barrier height ( Φ B0), series resistance ( R s), depletion layer width ( W D) and dopping concentration ( N D) of Al–TiW–Pd 2Si/ n-Si Schottky barrier diodes (SBDs) have been investigated by using the forward and reverse bias current–voltage ( I– V), capacitance–voltage ( C– V) and conductance–voltage ( G/ ω- V) measurements in dark and under illumination conditions at room temperature. The values of C and G/ ω increase with increasing illumination intensity due to the illumination induced electron–hole pairs in the depletion region. The density of interface states ( N ss) distribution profiles as a function of ( E c − E ss) was extracted from the forward I– V measurements by taking into account the bias dependence of the effective barrier heights ( Φ e) for device in dark and under various illumination intensities. The high values of N ss were responsible for the nonideal behavior of I– V, C– V and G/ ω characteristics. The values of R s obtained from Cheung and Nicollian methods decrease with increasing illumination intensity. The high values of n and R s have been attributed to the particular distribution of N ss, surface preparation, inhomogeneity of interfacial layer and barrier height at metal/semiconductor (M/S) interface. As a result, the characteristics of SBD are affected not only in N ss but also in R s, and these two parameters strongly influence the electrical parameters.

Exponential dependence of potential barrier height on biased voltages of inorganic/organic static induction transistor

The exponential dependence of the potential barrier height ϕc on the biased voltages of the inorganic/organic static induction transistor (SIT/OSIT) through a normalized approach in the low-current regime is presented. It shows a more accurate description than the linear expression of the potential barrier height. Through the verification of the numerical calculated and experimental results, the exponential dependence of ϕc on the applied biases can be used to derive the I–V characteristics. For both SIT and OSIT, the calculated results, using the presented relationship, are agreeable with the experimental results. Compared to the previous linear relationship, the exponential description of ϕc can contribute effectively to reduce the error between the theoretical and experimental results of the I–V characteristics.

Effect of series resistance on the electrical characteristics and interface state energy distributions of Sn/ p-Si (MS) Schottky diodes

In this study, electrical characteristics of the Sn/ p-type Si (MS) Schottky diodes have been investigated by current–voltage ( I– V) and capacitance–voltage ( C– V) measurements at room temperature. The barrier height obtained from C– V measurement is higher than obtained from I– V measurement and this discrepancy can be explained by introducing a spatial distribution of barrier heights due to barrier height inhomogeneities, which are available at the nanostructure Sn/ p-Si interface. A modified Norde’s function combined with conventional forward I– V method was used to extract the parameters including barrier height (Φ b ) and the series resistance ( R S ). The barrier height and series resistance obtained from Norde’s function was compared with those from Cheung functions. In addition, the interface-state density ( N SS ) as a function of energy distribution ( 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 b ) and series resistance ( R S ) for the Schottky diodes. While the interface-state density ( N SS ) calculated without taking into account series resistance ( R S ) has increased exponentially with bias from 4.235 × 10 12 cm −2eV −1 in ( E SS – 0.62) eV to 2.371 × 10 13 cm −2eV −1 in ( E SS – 0.39) eV of p-Si, the N SS obtained taking into account the series resistance has increased exponentially with bias from of 4.235 × 10 12 to 1.671 × 10 13 cm −2eV −1 in the same interval. This behaviour is attributed to the passivation of the p-doped Si surface with the presence of thin interfacial insulator layer between the metal and semiconductor.

The effects of surface states and series resistance on the performance of Au/SnO2/n-Si and Al/SnO2/p-Si (MIS) Schottky barrier diodes

Abstract We have fabricated two types of Schottky barrier(SBDs),Au/SnO2/n-Si (MIS1) and Al/SnO2/p-Si (MIS2), to investigate the surface (Nss) and series resistance (Rs) effect on main electrical parameters such as zero-bias barrier height (ΦBo) and ideality factor (n) for these SBDs. The forward and reverse bias current–voltage (I–V) characteristics of them were measured at 200 and 295 K, and experimental results were compared with each other. At temperatures of 200 and 295 K, ΦBo, n, Nss and Rs for MIS1 Schottky diodes (SDs) ranged from 0.393 to 0.585 eV, 5.70 to 4.75, 5.42×1013 to 4.27×1013 eV−1 cm−2 and 514 to 388 Ω, respectively, whereas for MIS2 they ranged from 0.377 to 0.556 eV, 3.58 to 2.1, 1.25×1014 to 3.30×1014 eV−1 cm−2 and 312 to 290 Ω, respectively. The values of n for two types of SBDs are rather than unity and this behavior has been attributed to the particular distribution of Nss and interfacial insulator layer at the metal/semiconductor interface. In addition, the temperature dependence energy density distribution profiles of Nss for both MIS1 and MIS2 SBDs were obtained from the forward bias I–V characteristics by taking into account the bias dependence of effective barrier height (Φe) and Rs. Experimental results show that both Nss and Rs values should be taken into account in the forward bias I–V characteristics. It has been concluded that the p-type SBD (MIS2) shows a lower barrier height (BH), lower Rs, n and Nss compared to n-type SBD (MIS1), which results in higher current at both 200 and 295 K.

Field dependence of barrier heights and luminescence properties in polar and nonpolar InGaN/GaN single quantum wells

The external field dependence of barrier heights and the internal field dependence of luminescence properties in InxGa1−xN/GaN single quantum wells (SQWs) with polar (x=0.13) and nonpolar (x=0.15) orientations were investigated. The conduction band offset of a SQW was characterized by using deep level transient spectroscopy. At a reverse bias of −3 V, the barrier height of the nonpolar SQW was estimated to be 0.42 eV, which is smaller than the 0.60 eV seen in the polar SQW due to the absence of internal fields along the nonpolar direction. Both samples showed a redshift of barrier heights with increasing reverse bias. The carrier recombination affected by carrier localization, quantum-confined Stark effect, and Varshni’s shift was analyzed through temperature-dependent photoluminescence. Numerical simulations of the barrier heights and internal fields showed good agreement with experimental results.

Electronegativity equalization model for interface barrier formation at reactive metal/organic contacts

A general model based on electronegativity equalization method (EEM) is proposed for a quantitative formulation of barrier formation at reactive metal/organic interfaces. The present model predicts for molecular bonding formation a linear dependence of barrier heights on the degree of partial charge transfer, which is determined by the electronegativity difference between metals and molecules. Also, the calculated barrier heights show good agreement with the empirical values. It suggests that the EEM-based electronegativity model has captured the essence of barrier formation at reactive metal/organic interfaces, and that electronegativity is a fundamental factor in characterizing the chemical trend of barrier heights.

The role of 60Co γ-ray irradiation on the interface states and series resistance in MIS structures

The effect of γ-ray exposure on the metal–insulator–semiconductor (MIS) structures has been investigated using the electrical characteristics at room temperature. The MIS structures are irradiated with 60Co γ-ray source. The energy distribution of interface states was determined from the forward bias I– V characteristics by taking into account the bias dependence of the effective barrier height and ideality factor. The value of series resistance decreases with increasing dose. Experimental results confirmed that γ-ray irradiation have a significant effect on electrical characteristics of MIS structures.

Strong surface Fermi level pinning and surface state density in GaAs0.65Sb0.35 surface intrinsic-n+ structure

Room-temperature photoreflectance is employed to investigate the Fermi level pinning and surface state density of a GaAs0.65Sb0.35 surface intrinsic-n+ (SIN+) structure. Based on the thermionic emission theory and current-transport theory, the surface Fermi level VF and surface state density are determined experimentally from the dependence of the surface barrier height on the pump beam intensity. The surface state density Ds is estimated as approximately 1.91×1013 cm−2, and the Fermi level is located 0.63 eV below the conduction band edge at the surface. By sequential etching of the intrinsic layer, the Fermi level pinning in GaAs0.65Sb0.35 SIN+ structure is further demonstrated.