High Schottky Barrier Research Articles

Surface passivation and interface reactions induced by hydrogen peroxide treatment of n-type ZnO (0001¯)

X-ray photoemission spectroscopy and electrical measurements have been employed to study O-face (0001¯) n-type ZnO samples treated by hydrogen peroxide (H2O2). A highly resistive and oxygen-rich surface layer is revealed, presumably caused by a high concentration of zinc vacancies and/or adsorbed O2 molecules. As a result, the surface exhibits upward energy band bending (∼0.4 eV) promoting the formation of high barrier Schottky contacts and suppressing the surface leakage current. Furthermore, after Pd deposition an enhanced formation of PdO is found at the Pd/ZnO interface for the H2O2-treated samples, and this is also expected to increase the resulting Schottky barrier height (∼0.6 eV), which yields up to seven orders of magnitude in current rectification between forward and reverse bias voltage.

Temperature-Dependent Characteristics of a Low Temperature Deposition Approach on a Pseudomorphic High Electron Mobility Transistor

The temperature-dependent characteristics of an AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) with an electroless plated (EP) deposition approach are studied and demonstrated. Based on the low temperature and low energy deposition, the EP deposition approach can form a better metal-semiconductor interface with the reduction in surface damage. Experimentally, the EP-based device shows a significantly improved dc performance. Good experimental results, including a high Schottky barrier height of 0.831 (0.759) eV, low ideality factor of 1.10 (1.32), high turn-on voltage of 0.75 (0.51) V, low reverse leakage current of 3.9 (161.4) μA/mm, improved threshold voltage of -0.43 (-0.61) V, and high maximum transconductance of 225.8 (160.9) mS/mm, are obtained at 300 (500) K. Moreover, the EP approach also has the advantages of easy operation and low cost.

CMOS Scaling For the Next Decade: Trends, Challenges and Opportunities

The advent of high-k/metal gates into production for CMOS gate stacks has marked the onset of MOSFET scaling that has clearly become reliant on new materials and / or new device architecture. Additionally, new approaches to form ultra-shallow junctions with high active-dopant concentrations and low schottky barrier height silicides with novel materials to reduce contact resistance have been reported by many groups and will continue to facilitate MOSFET scaling with increasing performance. It is becoming clear that Si (as the channel) may not be able to provide for the high performance combined with low power technologies that would be needed in future. Over several years, there has been a lot of research on high mobility channels: group IV for pMOSFETs and III-V for NMOSFETs. However, there appears to be little consensus on a) the choice of high mobility channels for P and N channel MOSFETs, b) its potential compared to short channel strained-Si, and 3) potential technology node for insertion. In this work, trends, challenges and opportunities related to several of the aforementioned modules (gate stack, junctions, contacts, and high mobility Ge based channels) will be briefly presented and discussed.

High quality GaN-based Schottky barrier diodes

We report the fabrication of GaN-based Schottky barrier diodes with multi-MgxNy/GaN buffer. Compared to conventional devices with a low-temperature GaN buffer, we achieved a six orders of magnitude smaller leakage current. It was also found that effective Schottky barrier height is larger for the proposed device due to the reduction in surface defect density by using the multi-MgxNy/GaN buffer.

A high Schottky barrier between Ni and S-passivated n-type Si(1 0 0) surface

By minimizing surface states with sulfur passivation, a record-high Schottky barrier is achieved with nickel on n-type Si(100) surface. Capacitance–voltage measurements yield a flat-band barrier height of 0.97eV. Activation-energy and current–voltage measurements indicate ∼0.2-eV lower barriers for the Ni/Si(100) junction. These results accompany a previously-reported record-high Schottky barrier of 1.1eV between aluminum and S-passivated p-type Si(100) surface. The operation of these metal/Si(100) junctions changes from majority-carrier conduction, i.e., a Schottky junction, to minority-carrier conduction, i.e., a p–n junction, with the increase in barrier height from 0.97eV to 1.1eV. Temperature-dependent current–voltage measurements reveal that the Ni/S-passivated n-type Si(100) junction is stable up to 110°C.

Porous silver-TiO 2 Schottky-type chemical sensor fabricated on thermally oxidised titanium

The fabrication and characterisation of silver-rutile junctions, formed by sintering silver particles on a thermally oxidised titanium single crystal, are reported. Operating in air at elevated temperatures, these devices were low leakage current and high barrier Schottky diodes, while in highly reducing atmospheres they behaved as ohmic contacts. This reversible transition afforded a broad dynamic range and high sensitivity for chemical detection. The reverse current increased ∼106 times when 1% butanol vapour was introduced to the surrounding clean air. The fabrication method described can also be employed to make other noble metal-rutile diodes.

희토류 금속을 이용한 니켈 실리사이드의 전기 및 물리적 특성

In this paper, we investigated electrical and physical characteristics of nickel silicide using rare-earth metals(Er, Yb, Tb, Dy), Incorporated Ytterbium into Ni-silicide is proposed to reduce work function of Ni-silicide for nickel silicided schottky barrier diode (Ni-silicided SBD). Nickel silicide makes ohmic-contact or low schottky barrier height with p-type silicon because of similar work function () in comparison with p-type silicon. However, high schottky barrier height is formed between Ni-silicide and p-type substrate by depositing thin ytterbium layer prior to Ni deposition. Even though the ytterbium is deposited below nickel, ternary phase is formed at the top and inner region of Ni-silicide, which is believed to result in reduction of work function about 0.15 - 0.38 eV.

Relieved kink effects in symmetrically graded In0.45Al0.55As∕InxGa1−xAs metamorphic high-electron-mobility transistors

Kink effects in an In-rich InxGa1−xAs (x=0.53–0.63) linearly graded channel of an In0.45Al0.55As∕InxGa1−xAs metamorphic high-electron-mobility transistor have been effectively relieved by depositing a high-barrier Ni∕Au gate with the silicon nitride passivation. Complete physical investigations for the relieved kink effects have been made by comparing identical devices with/without a high-barrier Schottky gate or the surface passivation. After successfully suppressing the kink effects, the proposed device has shown a superior voltage gain of 173.8, low output conductance of 2.09mS∕mm, and excellent power-added efficiency of 54.1% with high output power (power gain) of 14.87dBm (14.53dB). Improved linearity and excellent thermal threshold coefficient (∂Vth∕∂T) of −0.14mV∕K have also been achieved. The proposed design provides good potential for high-gain and high-linearity circuit applications.

Low leakage Schottky rectifiers fabricated on homoepitaxial GaN

The development of a vertical GaN Schottky rectifier on freestanding bulk GaN substrate by employing homoepitaxial growth technique is reported. The n−∕n+ Schottky diode structure was grown on conductive GaN substrate by metal-organic chemical vapor deposition. The dislocation density of the homoepitaxial layer determined by cathodoluminescence mapping technique is ∼6×106cm−2 with surface roughness less than 1nm. The fabricated Schottky rectifiers with dielectric overlap edge termination show a low reverse leakage current of <3×10−8A at −100V, which can be explained by the low dislocation density in the epilayer and high Schottky barrier height (1.37eV) of the Pt∕GaN metal-semiconductor contact. Due to the reduced series resistance, the bulk GaN Schottky rectifiers also exhibit a low turn-on voltage of ∼1.3V and an on-resistance of ∼5.3mΩcm2.

Improvement of SBD Electronic Characteristics Using Sacrificial Oxidation Removing the Degraded Layer from SiC Surface after High Temperature Annealing

Ion implantation and a subsequent annealing at high temperature are required for fabricating a high voltage Schottky Barrier Diode (SBD) with a field limiting ring (FLR) or a junction termination extension (JTE), but high temperature annealing degrades surface condition of a SiC substrate and induces a degradation of electronic characteristics of a fabricated SBD. To avoid a degradation of SBD electronic characteristics after high temperature annealing, the method of removing a degraded layer from a SiC surface by sacrificial oxidation after high temperature annealing is studied. In this study, we studied the relationship between the improvement of SBD electronic characteristics and the thickness of sacrificial oxide grown after high temperature annealing. 9~12 SBD without edge termination were fabricated on a SiC substrate of 4mm×4mm. The ratio of good chips to all chips (9~12 SBD) increases with increasing total thickness of sacrificial oxide grown after high temperature annealing at 1800oC for 30 s, where an SBD with a leakage current less than 1μA/cm2 at reverse voltage of –100V was defined as a good chip. We applied this process growing sacrificial oxide of 150nm after high temperature annealing to fabricate the SBD with an FLR structure designed with 600V blocking voltage on a Si-face SiC substrate. The SBD with an FLR structure through this process of 150 nm sacrificial oxide is low leakage current of less than 1μA/cm2 at reverse voltage of –100V and achieves 600V blocking voltage, however, the SBD with an FLR structure without the process of sacrificial oxide after high temperature annealing is high leakage current at reverse voltage of –100V. It is shown that this process growing sacrificial oxide after high temperature annealing is useful to fabricate an SBD with an FLR structure.

Output properties of C60 field-effect transistors with different source/drain electrodes

C 60 field-effect transistors (FETs) have been fabricated with source/drain electrodes of three different materials, indium tin oxide (ITO), Au, and Pt. High field-effect mobility μFE of FETs with ITO electrodes, 1.6×10−1cm2∕Vs, shows that ITO is a potential material for the electrodes of organic electronics. Although the highest Schottky barrier and the lowest μFE were expected, μFE of FET with Pt electrodes (1.4×10−1cm2∕Vs) is higher than that of FET with Au electrodes (9.6×10−2cm2∕Vs). The result suggests that modification of local electronic structure at the interface between electrodes and C60 affects device performance.

High efficiency 4H-SiC Schottky UV-photodiodes using self-aligned semitransparent contacts

Abstract In this work, we report on 4H-SiC vertical Schottky UV-photodiodes, with a novel “semitransparent” electrode, using self-aligned Ni 2 Si interdigit contacts, that allow operation in the pinch-off regime of the directly exposed optically active area. This improves short wavelength detector sensitivity with respect to conventional semitransparent Schottky UV detectors which use thin metal films. Computer simulations of the electric field distribution were used to optimise the device’s front electrode geometry, maximising the pinch-off surface effect. The detector dark current was about 200 pA at −50 V thanks to the high Schottky barrier of the Ni 2 Si on the 4H-SiC (1.66 eV). Under illumination with radiation at 254 nm, an increase of the current of more than two orders of magnitude is observed, resulting in 78% internal quantum efficiency. The vertical photodiodes showed an ultraviolet–visible rejection ratio of about 10 4 and a current responsivity factor of 1.8 higher than a conventional planar metal–semiconductor–metal interdigit structure.

Sensing Mechanism of InP Hydrogen Sensors Using Pt Schottky Diodes Formed by Electrochemical Process

Hydrogen sensing characteristics of Pt/InP Schottky diodes fabricated by electro-deposition were investigated. Such diodes gave high Schottky barrier heights (SBHs) of 650–810 meV. Upon exposure to hydrogen in air, the diodes exhibited a remarkable increase in forward and reverse currents. The saturation current on a log scale and the transient speed changed in proportion to the square root of the hydrogen pressure, PH2. Upon exposure to hydrogen in vacuum or in nitrogen, a much larger and much faster increase in current took place. However, the saturation current was almost independent of PH2, and the current increase remained almost the same after the hydrogen was removed. The sensing mechanism is explained in terms of changes in SBH caused by interface dipoles formed at Pt/InP interfaces due to adsorbed atomic hydrogen. Transient waveforms and dependence of saturation current and transient time constant on PH2 were explained quantitatively by a simple theory where processes including atomic hydrogen generation, transport, storage, adsorption, desorption, and reaction with oxygen are effectively included.

Improved InAlGaP-based heterostructure field-effect transistors

This investigation proposes the improved double δ-doped InGaP/InGaAs heterostructure field-effect transistor (HFET) grown by metalorganic chemical vapour deposition. The extrinsic transconductance (gm) and saturation current density (Imax) of the double δ-doped InGaP/InGaAs HFET are superior to those of the previously reported single δ-doped InGaP/InGaAs HFETs. The first n-InAlGaP/GaAs HFET is also investigated because it has a high Schottky barrier, a large high band gap and a large conduction-band discontinuity (ΔEC). Even without indium in the channel of the InAlGaP/GaAs HFET, gm and Imax are as high as 170 mS mm−1 and 410 mA mm−1, respectively. The gm values of these two HFETs remain large even when the gate voltages are positive. Moreover, the breakdown voltages of the two examined HFETs both exceed 40 V.

Fabrication of poly-Si TFT with silicided Schottky barrier source/drain, high-κ gate dielectric and metal gate

In this paper, a polycrystalline Si thin film transistor (TFT) with self-aligned silicide Schottky barrier source/drain (SSD), high-κ gate dielectric and metal gate electrode is demonstrated using a simplified low temperature process. After crystallization of α-Si, the thermal budget for device fabrication is reduced to ∼420 °C due to elimination of the implant doping and subsequent activation annealing procedures. P-channel SSD-TFT with PtSi S/D shows an acceptable electrical performance with I on of 1.5 μA/μm for the L g = 2.5 μm device at V gs = V ds = −5 V and I on/ I off ratio of ∼10 4. However, I on of the n-channel SSD-TFT with DySi 2− x S/D is about two orders of magnitude smaller due to the relatively high Schottky barrier height and poor silicide quality of the DySi 2− x /poly-Si contact.

On the suppression of hydrogen degradation in PbZr0.4Ti0.6O3 ferroelectric capacitors with PtOx top electrode

The effect of oxygen content in the sputtered Pt oxide (PtOx, x=0.4∼1), top electrode on suppressing the hydrogen degradation of ferroelectric capacitors of PbZr0.4Ti0.6O3 (PZT) was studied. It was found that the ferroelectric property becomes significantly degraded along with a positive voltage offset in the polarization-field hysteresis loop after forming gas (N2+H2) annealing at 200°C of the PZT capacitors made with Pt top electrode. The leakage current in the degraded capacitors also greatly increases due to the reduction of Schottky barrier. However, the degradation of electrical property can be suppressed by using PtOx as top electrode, and the ferroelectric characteristics are well retained ever for capacitors with size shrunk down to submicron scale. The secondary-ion-mass spectroscopy and elastic recoil detection analysis reveal that the catalytic reaction of Pt in dissociation of hydrogen molecules from forming gas can be effectively interrupted by increasing the oxygen content in the PtOx electrode, and the property degradation induced from hydrogen segregation at the interface and incorporation with the PZT layer is thus suppressed. In addition to the superior hydrogen blocking capability, which prevents the detrimental effect of hydrogen doping, a high Schottky barrier is also obtained from the high work function of PtOx electrode.

High Performance P-Channel Schottky Barrier MOSFETs withSelf-Aligned PtSi Source/Drain on Thin Film SOI Substrate

P-channel metal-oxide-semiconductor field-effect transistors (MOSFETs)with PtSi Schottky barrier source/drain, high-k gate dielectric andmetal gate electrode were fabricated on a thin p-typesilicon-on-insulator (SOI) substrate using a simplified low temperatureprocess. The device works on a fully-depleted accumulation-mode and hasan excellent electrical performance. It reaches Ion/Ioffratio of about 107, subthreshold swing of 65 mV/decade andsaturation drain current of Ids = 8.8 μA/μm at|Vg−Vth| = |Vd| = 1 V for devices with the channellength 4.0 μm and the equivalent oxide thickness 2.0 nm. Comparedto the corresponding bulk-Si counterparts, SOI p-SBMOSFETs have smalleroff-state current due to reduction of the PtSi/Si contact area.

Mechanism of Ambipolar Field-Effect Carrier Injections in One-Dimensional Mott Insulators

To clarify the mechanism of recently reported, ambipolar carrier injections into quasi-one-dimensional Mott insulators on which field-effect transistors are fabricated, we employ the one-dimensional Hubbard model attached to a tight-binding model for source and drain electrodes. To take account of the formation of Schottky barriers, we add scalar and vector potentials, which satisfy the Poisson equation with boundary values depending on the drain voltage, the gate bias, and the work-function difference. The current-voltage characteristics are obtained by solving the time-dependent Schr\"odinger equation in the unrestricted Hartree-Fock approximation. Its validity is discussed with the help of the Lanczos method applied to small systems. We find generally ambipolar carrier injections in Mott insulators even if the work function of the crystal is quite different from that of the electrodes. They result from balancing the correlation effect with the barrier effect. For the gate-bias polarity with higher Schottky barriers, the correlation effect is weakened accordingly, owing to collective transport in the one-dimensional correlated electron systems.

AlGaN/GaN field effect Schottky barrier diode (FESBD)

We demonstrate a novel field effect Schottky barrier diode (FESBD) with a dual Schottky structure combined with an AlGaN/GaN heterostructure to obtain a low on-voltage. The vertical and planar FESBDs were tried. A vertical AlGaN/GaN heterostructure was regrown by a selective area growth (SAG) technique using a metalorganic chemical vapor deposition (MOCVD). The contact layer was also grown using an SAG technique. Dual Schottky structures were fabricated to obtain a low on-voltage. That is, Al/Ti was used for a low Schottky barrier metal and Pt used for a higher barrier metal. The on-voltage of the diode was below 0.1 V. By the pinch-off effect of a higher Schottky barrier electrode, the reverse breakdown voltage was over 400 V although the Al/Ti used for a low Schottky barrier metal showed an ohmic property. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

ShOC rectifier: a new metal-semiconductor device with excellent forward and reverse characteristics

We report a new structure, called the shielded ohmic contact (ShOC) rectifier which utilizes trenches filled with a high-barrier metal to shield an Ohmic contact during the reverse bias. When the device is forward biased, the ohmic contact conducts with a low forward drop. However, when reverse biased, the Ohmic contact is completely shielded by the high-barrier Schottky contact resulting in a low reverse leakage current. Two dimensional numerical simulation is used to evaluate and explain the superior performance of the proposed ShOC rectifier.