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.     

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].     

Current-voltage analysis of a-Si:H Schottky diodes

Direct current (dc)-voltage (I-V) characteristics of the hydrogenated amorphous silicon (a-Si:H) Schottky diode have been measured at different temperatures under dark and light. From the fourth quadrant of illuminated characteristics, fill factor (FF) values were obtained for each temperature measured (173-297 K). We have found that FF increases very little as the temperature is decreased. The measured data from I-V characteristics has been analyzed in detail. In particular, from dark I-V characteristics obtained, the density of state (DOS) near the Fermi level was determined using a simple model based on the space-charge limited current (SCLC). On the other hand, from the illuminated I-V characteristics, the density of carriers was calculated for each temperature using the analysis of diode equation as known. A comparison of the carrier density and the measured photocurrent as a function of the reverse temperature was also made and a good correspondence was obtained.     

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.     

A note on TiN/Si (1 0 0) contacts

The contact properties of TiN on p- and n-type Si (1 0 0) obtained by magnetron reactive sputtering were investigated. Schottky diode characteristics were observed on p-type Si (1 0 0) as determined by forward current-voltage (I-V) measurements, but on n-type Si (1 0 0) the reverse I-V relation has shown a nonsymmetrical character. The zero-bias barrier heights evaluated by I-V on both type diodes were in the range of ∼0.60-0.64 V within the range of a few mVs, not more than ∼±(10-30) mV from each other. Incorporation of the effect of the series resistance in the I-V analysis resulted in a significant reduction in the magnitude of the ideality factor of the TiN/p-type specimen. Almost no change has occurred in the barrier height values. The contradictory reports on the TiN/n-type Si (1 0 0) diode characteristics in earlier works have been explained in terms of surface passivation of Si by the HF cleaning solution. It was stated in these reports that following annealing at 673 K the diodes have shown rectifying behavior. It has been speculated, that the nonsymmetrical nature of the TiN/n-Si (1 0 0) showing an intermediate behavior between Ohmic and rectifying behavior is a result of the specimen being exposed to a temperature lower than 673 K during sputtering where no complete depassivation took place. In order to obtain a rectifying behavior of TiN on both n-type and p-type Si surface passivation has to be eliminated.     

Inhomogeneities in 130 MeV Au ion irradiated Au/n-Si (1 0 0) Schottky structure

The electrical characteristics of Au/n-Si (1 0 0) Schottky rectifier have been studied in a wide irradiation fluence range using conventional current-voltage (I-V) and capacitance-voltage (C-V) measurements. The I-V characteristics showed an abnormal increase in forward current at low voltage. The device shows a bend in forward I-V and reverses bias C-V characteristics due to extra current, suggesting that there are two independent contributions to thermionic current, corresponding to two levels of the Schottky barrier. It is shown that the excess current at low voltage can be explained by taking into account the role of heavy ion irradiation induced defects at the metal semiconductor interface.     

Characterization of conductance under finite bias for a self-assembled monolayer coated Au quantized point contact

We have demonstrated that an experimental cross-wire junction set-up can be used to measure the I-V characteristics of a self-assembled monolayer (SAM) stabilized metal quantized point contact. The increased stability due to the presence of the SAM allows the measurement of the I-V characteristics. However, the SAM also provides additional conductance paths in addition to the pure metal point contact. The presence of the SAM may contribute to the non-integral quantum conductance transition and the non-linear I-V characteristics of the quantum contact. Nonetheless, a straight I-V curve is obtained for the Au quantized point contact from 0 to 1 V with a conductance of approximately 1G₀, in contrast to previous work reported in the literature.     

The effects of annealing on Au/pyronine-B/MD n-InP Schottky structure

Thin film of non-polymeric organic compound pyronine-B has been fabricated on moderately doped (MD) n-InP substrate as an interfacial layer using spin coating technique for the electronic modification of Au/MD n-InP Schottky contact. The electrical characteristics have been determined at room temperature. The barrier height and the ideality factor values for Au/pyronine-B/MD n-InP Schottky diode have been obtained from the forward bias I-V characteristics at room temperature as 0.60 eV and 1.041; 0.571 and 1.253 eV after annealing at 100 and 250 °C, respectively. An increase in annealing temperature at the Au/n-InP Schottky junction is shown to increase the reverse bias leakage current by about one order of magnitude and decrease the Schottky barrier height by 0.027 eV. Furthermore, the barrier height values for the Au/pyronine-B/MD n-InP Schottky diode have also been obtained from the C-V characteristics at room temperature as 1.001 and 0.709 eV after annealing at 100 and 250 °C, respectively. Finally, it was seen that the diode parameters changed with increase in the annealing temperature.     

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.     

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.     

Electron conduction associated with the chemical transport of reducing elements in oxide cathode for CRT's application

In the present work, the formation of compounds associated to the diffusion of reducing elements (Mg, Al and W) to the Ni cap surface of oxide cathode has been studied by a new method. This method used two cathodes, one of them is coated and the other is uncoated, to be in an attach-contact mounted in a dummy tube. Different analytical techniques were used for this study: scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX) and I/V electrical measurements. After oxide cathode plus decomposited and activated, Al and Mg doping elements take place during heating to 810 °C (Ni-Br) under a rich controlled Ba/SrO atmosphere through an acceleration life test.It is shown that the chemical transport occurs mainly by a grain boundary mechanism with significant pile-up of Mg compounds. Al and W show a superficial concentrations and distribution.The dc electrical characteristic shows very strong rectifying behaviour through the M-S junction due to the I/V curves, particularly after 144 h acceleration life time. The characteristics are found to be reversible and reproducible, and viewed a rectification ratio (r) of 100. The calculated ideality factor shows a value of n = 9.6, which is evidenced to the tunnelling conduction.The theoretical calculation shows that the interface thickness grows to (∼6 μm) after accelerated the cathode to 1896 h.     

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.     

Carbon nanotube field emission cathodes fabricated with trivalent chromium conversion coated substrates

The properties of carbon nanotube (CNT) field emission cathodes fabricated by a dip coating method with trivalent chromium conversion coated substrates are studied. Two kinds of substrates with different morphologies, one with a rough crackled surface and the other with a smooth surface, were used for making the CNT cathodes, and their I-V curves and emission patterns were evaluated. The results show that, as compared to the smooth substrate surface, the rough surface with self-assembled sub-micro-cracks on the substrate can dramatically enhance the uniformity of the emission pattern and the emission efficiency. The cathode fabricated with the crackled substrate shows good field emission properties such as high brightness, good uniformity, a low turn-on field (0.86 V/μm) and a high current density of 10 mA/cm² at 2.5 V/μm.     

Electrical characteristics of insulating aluminum nitride MIS nanostructures

Capacitance-voltage measurements of high quality PECVD and MBE grown aluminum nitride (AlN) thin films have been performed. The prepared films have shown polycrystalline (0 0 2)-preferential orientation, and were deposited on p-type Si (1 0 0) substrates with Pt forming the metal gate in a metal-insulator-semiconductor (MIS) configuration. The structure, crystallinity, texture and insulating properties have been found to depend on film thickness and were substantially influenced by the increase of the thickness. C-V measurements of the epitaxial and PECVD films were carried out and their insulating characteristics with increasing thickness (200-1000 nm) were investigated. The epitaxial films exhibited no hysteresis in capacitance behaviour, owing to better crystalline quality over the PECVD grown ones. Capacitance curves versus bias voltage have also been acquired at different temperatures; 10 K, 30 K and 50 K for deposited polycrystalline AlN films of (0 0 2) orientation. We have found that the defects trapped in the Pt/AlN/Si structure played a key role in dominating the overall behaviour of the C-V measurement curves. The trapped charges at the interface between the AlN insulating film and Si substrate caused the capacitance characteristics to shift to negative voltages, and the estimated charge density was of the order of 10¹⁰ and 10⁸ cm⁻² eV⁻¹ for the PECVD and epitaxial samples respectively. The I-V measurements referred to space-charge conduction mechanism, and the deduced leakage current was found to be of the order of 10⁻⁹ A at 200 nm film thickness.     

A comparative study of thermionic emission from vertically grown carbon nanotubes and tungsten cathodes

Thermionic emission from vertically grown carbon nanotubes (CNTs) by water-assisted chemical vapor deposition (WA-CVD) is investigated. I-V characteristics of WA-CNT samples exhibit strong Schottky effect leading to field proportionality factor β ∼ 10⁴ cm⁻¹in contrast to β ∼ 200 cm⁻¹ for the bare tungsten substrate. Non-contact atomic force microscopy imaging of CNT samples show propensity of nanoasperities over a scale of micron size over which the tungsten surface is seen to be atomically smooth. The values of root mean-square roughness for CNTs and W were found to be 24.2 nm and 0.44 nm respectively. The Richardson-Dushman plots yield work function values of Φ_CNT ? 4.5 and Φ_W ? 4.3 eV. Current versus time data shows that CNT cathodes are fifteen times noisier than tungsten cathode presumably due to increased importance of individual atomic events on the sharp CNT tips of bristle like structures. Power spectral density of current exhibited 1/f^ξ behavior with ξ ? 1.5, and 2 for W and CNTs. The former suggests surface diffusion whereas the latter indicates adsorption/desorption of atomic/molecular species as a dominant mechanism of noise generation.     

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.     

Investigation of electrical and ammonia sensing characteristics of Schottky barrier diode based on a single ultra-long ZnO nanorod

Novel ultra-long ZnO nanorods, with lengths about 0.5-1.5 mm and diameters ranging from 100 to 1000 nm, in mass production have been synthesized via the vapor-phase transport method with CuO catalyst at 900 °C. Rectifying Schottky barrier diodes have been fabricated by aligning a single ultra-long ZnO nanorod across paired Ag electrodes. The resulting current-voltage (I-V) characteristics of the SBD exhibit a clear rectifying behavior. The ideality factor of the diode is about 4.6, and the threshold voltage is about 0.54 V at room temperature (300 K). At the same time the detailed I-V characteristics have been investigated in the temperature range 423-523 K. In addition, after exposure of the Schottky diodes to NH₃, the forward and reverse currents increase rapidly, indicating a high sensitivity to NH₃ gas.     

Surface structure analysis of metal adsorbed Si(1 1 1) surfaces by Patterson function with LEED I-V curves

Wu and Tong proposed the calculation method of Patterson function obtained directly from the LEED I-V curves which shows the relative position of surface atoms as an image. We have made the calculation program of Patterson function and applied to the structural analysis of the Si(1 1 1)1 × 1-Fe surface. Surface structure was able to be expressed almost correctly by the Patterson function obtained from the theoretical I-V curves for the model structure. In the Patterson function obtained from the experimental I-V curves, the locational relation between the atoms of subsurface layer was in agreement with the CsCl type structure. More over, because the faint peak, by which we can distinguish the model, can be seen, it seems that the model B8 is preferable to the model A8. This result is consistent with the model shown by Walter et al.     

Effect of the oxidation process on SiO2/4H-SiC interface electrical characteristics

In this work we have compared the SiO₂/SiC interface electrical characteristics for three different oxidations processes (dry oxygen, water-containing oxygen and water-containing nitrogen atmospheres). MOS structures were fabricated on 8° off-axis 4H-SiC(0 0 0 1) n- and p-type epi-wafers. Electrical characteristics were obtained by I-V measurements, high-frequency capacitance-voltage (C-V) and ac conductance (G-ω) methods. Comparing the results, one observes remarkable differences between samples which underwent different oxidation routes. Among the MOS structures analyzed, the sample which underwent wet oxidation with oxygen as carrier gas presented the higher dielectric strength and lower values of interface states density.     

Investigation of the effects of porous layer on the electrical properties of Pt/n-GaN Schottky contacts

This article reports the effects of porosity on the enhancement of the Schottky barrier height (SBH) and reduction of the leakage current of Pt Schottky diode based on n-type GaN. The porous GaN layer in this work was generated by electroless chemical etching under UV illumination. For comparative study, two additional samples, i.e. one as-grown sample and one thermally treated sample, were also prepared. The structural studies showed that the porous GaN sample has a relatively rough surface morphology with slightly broader X-ray diffraction peak of the (0 0 0 2) plane. The current-voltage (I-V) measurements revealed that the electrical characteristics of the Pt Schottky diode were improved significantly by the presence of the porous layer, in which SBH was observed to be enhanced by 27%.