Schottky Barrier Characteristics Research Articles

Role of interfacial oxide layer thickness and annealing temperature on structural and electronic properties of Al/Ta2O5/TiO2/Si metal–insulator–semiconductor structure

In this study, we investigated the structural and electrical properties of TiO2/Ta2O5 stacks prepared using DC reactive magnetron co-sputtering for as-deposited films and films annealed at 700 °C. X-ray diffraction studies revealed that the as-deposited films were amorphous, whereas those annealed at 700 °C were polycrystalline with mixed phases of TiO2 and β-phase Ta2O5. The presence of mixed phases of TiO2 and β-phase Ta2O5 was also confirmed by Fourier-transform infrared spectroscopy. The optical band gap of the TiO2 films was 3.46 eV for the as-deposited films and decreased to 3.35 eV with increasing Ta2O5 layer thickness on TiO2. The films annealed at 700 °C showed a decrease in band gap to 3.32 eV for TiO2, and this value further decreased to 3.15 eV with increasing Ta2O5 layer thickness on TiO2. Furthermore, we investigated the electrical properties of the sputtered TiO2/Ta2O5 stacks fabricated on a metal–insulator–semiconductor (MIS) Al/Ta2O5/TiO2/p-Si Schottky diode. We studied the variation of the fundamental Schottky barrier characteristics (ideality factor, Schottky barrier, and series resistance) for a diode prepared using reactive magnetron sputtering with TiO2/Ta2O5 as a thin insulating layer at the Al/p-type Si interface with different thicknesses at both room temperature and 700 °C. Improved electrical characteristics were observed for the annealed Al/Ta2O5/TiO2/p-Si MIS Schottky structure compared with those of the as-deposited structure.

Analysis of temperature dependent forward characteristics of Ni/ β-Ga2O3 Schottky diodes

In this paper, the temperature dependence of the turn-on characteristics of Schottky barrier diodes fabricated on oriented n-type β-Ga2O3 is reported. The barrier height (qΦbn) and ideality factor (n) for Ni- β-Ga2O3 was found to be 1.08 ± 0.05 eV and 1.19 respectively at room temperature. The effective Richardson constant (A**) is determined to be 42.96 A cm−2 K−2, in close agreement with the theoretical value. At low temperatures (85–273 K), the current–voltage characteristics reveal a strong temperature dependence of Schottky barrier heights and ideality factors and a corresponding deviation from the barrier height extracted from capacitance–voltage measurements. A detailed analysis is presented, which suggest that these effects can be attributed to a large barrier inhomogeneity at metal/β-Ga2O3 interfaces, possibly resulting from interfacial defects, which can be modeled using a potential fluctuation model.

Laminated Mo/C Electrodes for 4H-SiC Schottky Barrier Diodes With Ideal Interface Characteristics

The electrical characteristics of SiC Schottky barrier diodes with laminated Mo/C electrodes having a Mo and C atom composition ratio of 2:1 have been investigated. High thermal stability against annealing up to a temperature of 1050 °C has been found as a diode characteristic. The almost identical values of Schottky barrier height for the electrons ( $\varPhi _{\mathrm {\mathbf {Bn}}})$ obtained in several measurements with the ideality factors of below 1.10 indicate the formation of an ideal Schottky contact with 4H-SiC substrates.

High performance and transparent multilayer MoS2 transistors: Tuning Schottky barrier characteristics

Various strategies and mechanisms have been suggested for investigating a Schottky contact behavior in molybdenum disulfide (MoS2) thin-film transistor (TFT), which are still in much debate and controversy. As one of promising breakthrough for transparent electronics with a high device performance, we have realized MoS2 TFTs with source/drain electrodes consisting of transparent bi-layers of a conducting oxide over a thin film of low work function metal. Intercalation of a low work function metal layer, such as aluminum, between MoS2 and transparent source/drain electrodes makes it possible to optimize the Schottky contact characteristics, resulting in about 24-fold and 3 orders of magnitude enhancement of the field-effect mobility and on-off current ratio, respectively, as well as transmittance of 87.4 % in the visible wavelength range.

Tunneling condition at high Schottky barrier and ambipolar transfer characteristics in zinc oxide semiconductor thin film transistor

This study investigates the behavior of SiOC as gate dielectric materials for zinc-based oxide semiconductor thin film transistors (TFTs). The SiOC with a high potential barrier due to a low ionic energy at a Poole–Frenkel (PF) contact was suitable for use as a gate dielectric material to support tunneling in ZnO/SiOC TFTs. The performance of the ZnO TFTs for the low-polarization SiOC improved by introducing a direct tunneling phenomenon in the minority carriers of the SiOC depletion layer due to the decrease in the activation energy and the very high Schottky barrier (SB) of the SiOC material. PF emission was achieved at a non-polar SiOC with a high SB, and the mobility-stability of the TFTs with the PF contact dramatically improved. The TFT of the PF contact with a high SB was free from a shift in the threshold voltage with a decrease of the drain voltage.

Temperature dependent electrical characteristics of Pt Schottky barriers fabricated on lightly and highly doped n-type 4H-SiC

The temperature dependent electronic characteristics of Pt Schottky barriers fabricated on lightly and relatively highly doped n-type 4H-SiC (1 × 1016 and 1 × 1018 cm−3) are comparatively investigated. It is found that the abnormal temperature dependence of barrier height and ideality factor estimated from the thermionic emission (TE) model for both lightly and highly doped samples could be successfully explained in terms of Gaussian distribution of inhomogeneous barrier heights. However, the estimated mean barrier height according to Gaussian distribution for the highly doped sample is much lower than the actual mean value from the capacitance–voltage (C–V) measurements. Interestingly, the values of barrier height from the thermionic field emission (TFE) model are found to be close to those from the C–V measurements, indicating that the TFE model is more appropriate to explain the electrical transport for the highly doped sample.

Schottky junction UV photodetector based on CdS and visible photodetector based on CdS:Cu quantum dots

We report the synthesis of cadmium sulphide (CdS) quantum dots (QD), copper doped cadmium sulphide (CdS:Cu) quantum dots and silver (Ag) nanoparticles embedded in polyvinyl alcohol (PVA) and fabrication of nano CdS (undoped and doped)–Ag Schottky barrier. Chemical route is followed for CdS, CdS:Cu and Ag nanoparticles synthesis. Sizes and shapes of CdS and Ag nanoparticles are obtained from UV–vis, PL, XRD, SEM, TEM, HRTEM, SAED and composition from EDS. Nano scale devices are fabricated with ITO/TPD/CdS (undoped/doped) nanocomposites (NCs)/Ag nanoparticles/Al to study the Schottky barrier characteristics. Current–voltage (I–V) characteristics of the as-fabricated devices are performed under dark and light environment which show the Schottky barrier characteristic of the devices. The Schottky junctions exhibit rectifying behavior in the dark. The as-fabricated nano scale Schottky devices are found to be sensitive to light sources differing in wavelength. We have seen that the responsivity as well as external quantum efficiency (EQE) of the devices increases after doping. The photo response and EQE of the devices are found to increase with decrease in QD size. For CdS–Ag (undoped and doped) Schottky devices EQE is higher in the UV region, whereas responsivity is higher for CdS–Ag Schottky devices (undoped) in the UV region and for CdS–Ag Schottky devices (doped) in the visible region.

Effects of atomic scale imperfection at the interfaces of CoSi2and Si (100) on Schottky barrier contacts

We report here the correlation of electrical properties on Schottky barrier contacts and atomic scale imperfections based on the degree of lattice distortion and moire fringes at the interfaces of CoSi2 and Si. The I-V measurements showed that the higher levels of perfection of the interfaces gave better Schottky barrier characteristics and we discuss the implications of the transport property at Schottky barrier contacts.

Transport characteristics of Pd Schottky barrier diodes on epitaxial n-GaSb as determined from temperature dependent current–voltage measurements

The temperature dependent transport characteristics of Pd/n-GaSb:Te Schottky contacts with low and saturating reverse current are investigated by means of current–voltage measurements between 80K and 320K. The apparent barrier height and ideality factor increase with a decrease in temperature. Neither thermionic nor thermionic field emission can explain the low temperature characteristics of these diodes. Instead, evidence is presented for barrier inhomogeneity across the metal/semiconductor contact. A plot of the barrier height, ϕb vs. 1/2kT revealed a double Gaussian distribution for the barrier height with ϕb,mean assuming values of 0.59eV±0.07 (80–140K) and 0.25eV±0.12 (140–320K) respectively.

Schottky barrier characteristics of Pt contacts to all sputtering-made n-type GaN and MOS diodes

All sputtering-made Pt/n-GaN [metal–semiconductor (MS)] and Pt/SiO2/n-GaN [metal–oxide–semiconductor (MOS)] diodes were investigated before and after annealing at 500 °C. n-GaN, Pt, and SiO2 films were all fabricated by the cost-effective radio-frequency sputtering technique. A cermet target was used for depositing GaN. The Schottky barrier heights (SBHs) of both MS and MOS Schottky diodes have been investigated by the current–voltage (I–V) measurements. The results showed that SBHs increased after annealing at 500 °C for 20 min in N2 ambient, compared to the as-deposited at 400 °C. By using Cheung’s and Norde methods, the highest SBHs of MOS Schottky diodes were respectively found to be 0.79 and 0.91 eV for the as-deposited and had reached to 0.81 and 0.94 eV after annealing. The annealed Schottky diode had showed the higher SBH, lower leakage current, smaller ideality factor, and denser microstructure.

Electrochemical growth of GaSe nanostructures and their Schottky barrier characteristics

Highly crystalline GaSe thin film was synthesized by electrochemical deposition technique on a silicon substrate. The X-ray diffractions showed a hexagonal crystal structure with preferential orientation along (004) plane. The scanning electron microscopy confirmed the homogenous distribution of deposited GaSe film along the silicon substrate. The high resolution electron microscopy showed that the GaSe nanoparticles have mean diameter of 23nm. The energy dispersion X-ray spectroscopy revealed a high purity of the as-deposited film. The junction characteristics of GaSe/n-Si diode were investigated. The current–voltage characteristics of the GaSe/n-Si were investigated in the temperature range 23–120°C. The I–V characteristics exhibit non-linearity indicating Schottky contact at the GaSe and n-Si interface. It was noticed the increase of current under the impact of light. Various device parameters such as series resistance, ideality factor and barrier height were estimated. The effect of temperature on the values of junction parameters was analyzed.

The Growth of 3-Inch 4H-SiC Si-Face Epitaxial Wafer with Vicinal Off-Angle

We grew epitaxial layers on 3-inch epitaxial wafers with a vicinal off-angle, using a horizontal hot-wall chemical vapor deposition system that had a reactor capacity of 3 x 150 mm. Uniformity (σ/mean) of thickness and carrier concentration as small as 1.7% and 5.6%, respectively, were successfully obtained. We succeeded in decreasing triangular surface defects and polytype inclusions by increasing the growth temperature and lowering the C/Si ratio. In addition, I-V characteristics of Schottky barrier diodes on an epitaxial layer showed that a high blocking voltage of 960 V and a low leakage current of less than 1 x 10-6 A/cm2 were obtained with a yield of 78%.

4H-SiC Homoepitaxial Growth on Substrate with Vicinal Off-Angle Lower than 1°

We investigated homoepitaxial growth on 4H-SiC Si-face substrate with a vicinal off-angle lower than 1°. The control of the wafer off-angle to a precision of 0.1° is important to controlling the surface morphology of homoepitaxial growth on this substrate. Keeping the C/Si ratio low by controlling the SiH4 flow rate was effective in striking balance between surface morphology and polytype homogeneity. Homoepitaxial layers were successfully grown on whole, 2-inch Si-face vicinal off-angled substrate without large step bunching or polytype inclusions. The quality of the epitaxial layer was confirmed by I-V characteristics of Schottky barrier diodes fabricated on the epitaxial wafer.

Forward Current Transport Mechanism and Schottky Barrier Characteristics of a Ni/Au Contact on n-GaN

The forward current transport mechanism and Schottky barrier characteristics of a Ni/Au contact on n-GaN are studied by using temperature-dependent current-voltage (T—I—V) and capacitance-voltage (C—V) measurements. The low-forward-bias I-V curve of the Schottky junction is found to be dominated by trap-assisted tunneling below 400 K, and thus can not be used to deduce the Schottky barrier height (SBH) based on the thermionic emission (TE) model. On the other hand, TE transport mechanism dominates the high-forward-bias region and a modified I—V method is adopted to deduce the effective barrier height. It is found that the estimated SBH (∼0.95 eV at 300K) by the I—V method is ∼0.20 eV lower than that obtained by the C—V method, which is explained by a barrier inhomogeneity model over the Schottky contact area.

Schottky barrier characteristics and internal gain mechanism of TiO2 UV detectors

High-responsivity metal-semiconductor-metal TiO(2) UV photodetectors with Ni and Au electrodes were fabricated identically. Their Schottky barrier heights and photocurrent gain mechanism were studied. The effective barrier height Φ and ideality factor n were evaluated according to the thermionic emission theory. The result that Φ(Ni) was lower than Φ(Au) may be attributed to the electron transfer from Ni to the TiO(2) substrate, which would lead to a dipole layer and, accordingly, decrease the barrier height. In addition, the I-V characteristics of the Ni/TiO(2)/Ni and Au/TiO(2)/Au photodetectors were observed. A significant internal gain was obtained, and the mechanism of the internal gain was studied by the phototransistor model in detail.

Effect of pressure on the characteristics of Schottky barrier diodes made of overcompensated semiconductor

Effect of pressure on the characteristics of Schottky barrier diodes made of overcompensated semiconductor

Electrodeposited PdNi as possible ferromagnetic contacts for carbon nanotubes

AbstractA process for electrodepositing PdNi alloys and subsequent characterisation studies are reported. PdNi alloys are deposited on 0.019–0.021 and 1–2 Ω cm n‐type silicon from a bath of Pd‐ethylenediamine dichloride and Ni sulphate. The deposited films form excellent Schottky barriers on 1–2 Ω cm Si with leakage currents of the order of µA/cm2 and forward current higher than the reverse current by about six orders of magnitude at 1 V. Ni atomic fractions in the deposited films are studied for different bath concentrations and the deposition potential was found to play an important role in deciding the composition of the deposited film. For high Ni concentration solutions, it is possible to deposit films with a wide range of Ni content by varying the deposition potential, while this method cannot be used with low Ni concentration solutions. Films with Ni concentrations above 30% were observed to be ferromagnetic at room temperature and ferromagnetic properties strengthened with Ni content. A structure for a carbon nanotube (CNT) transistor is described and electrical characterisation of the device using PdNi alloy contacts is presented. The Schottky barrier characteristics and ferromagnetic character make PdNi alloys a good material for ferromagnetic contacts to CNTs on a Si substrate.

Schottky Barrier Characteristics and Carrier Transport Mechanism for Ohmic Contacts to Strained p-Type InGaN/GaN Superlattice

We report on the metal work function dependence on Schottky barrier characteristics and the carrier transport mechanism for ohmic contacts to strained p-InGaN/GaN superlattices. Measurements showed that specific contact resistances are dependent on metal work functions, whereas Schottky barrier heights exhibit relatively little dependency on metal work functions. These indicate that the overall contact properties are directly affected by polarization-induced carriers near the surface of the strained InGaN. The carrier conduction mechanism for the contacts to the InGaN/GaN is described in terms of tunneling or compensation effect, depending on temperatures.

Heat- and radiation-resistant contacts to SiC made on the basis of quasi-amorphous ZrB2 films

The radiation and thermal stability of the Schottky-barrier structures deposited by the magnetron sputtering of zirconium diboride onto the (0001) face of the Lely-grown n-6H(15R)SiC single crystals with the uncompensated-donor concentration of ∼1018 cm−3 was investigated by the methods of the I–V and C–V characteristics combined with the layer-by-layer Auger analysis. It is shown that the use of quasi-amorphous ZrB2 films when manufacturing contacts on n-6H(15R)SiC leads to no changes in the Schottky-barrier characteristics during rapid thermal annealing to 800°C in the range of 60Co γ-ray irradiation doses of 103–107 Gy.

Silicon Schottky barrier photodiodes with a thin AlN nucleation layer

PurposeThe purpose of this paper is to present the characteristics of novel silicon Schottky barrier (SB) photodiodes (PDs) with aluminium nitride (AlN) (100 nm) nucleation layer.Design/methodology/approachComparison was made with conventional silicon SB PDs.FindingsIt was found that smaller dark current could be achieved with AlN nucleation layer. It was also found that effective SB height increased from 0.65 to 0.71 eV with the insertion of the AlN layer. The dark leakage current for the Schottky PDs with the AlN layer was shown to be about two orders of magnitude smaller than that for the conventional silicon SB PDs.Research limitations/implicationsIt is possible that the detrimental effect of interface states situated near the metal semiconductor interface was less pronounced for the sample owing to the insertion of the AlN nucleation layer.Originality/valueThere is believed to be no other report on silicon SB PDs capped with an AlN layer in the literature. This paper describes the fabricated silicon SB PDs and reports on the electrical characteristics of the devices with an AlN nucleation layer grown at low temperature.