Low Reverse Leakage Current Research Articles

Barrier height and ideality factor dependency on identically produced small Au/p-Si Schottky barrier diodes

Small high-quality Au/P-Si Schottky barrier diodes (SBDs) with an extremely low reverse leakage current using wet lithography were produced. Their effective barrier heights (BHs) and ideality factors from current-voltage (I–V) characteristics were measured by a conducting probe atomic force microscope (C-AFM). In spite of the identical preparation of the diodes there was a diode-to-diode variation in ideality factor and barrier height parameters. By extrapolating the plots the built in potential of the Au/p-Si contact was obtained as Vbi = 0.5425 V and the barrier height value ΦB(C-V) was calculated to be ΦB(C-V) = 0.7145 V for Au/p-Si. It is found that for the diodes with diameters smaller than 100 μm, the diode barrier height and ideality factor dependency to their diameters and correlation between the diode barrier height and its ideality factor are nonlinear, where similar to the earlier reported different metal semiconductor diodes in the literature, these parameters for the here manufactured diodes with diameters more than 100 μm are also linear. Based on the very obvious sub-nanometer C-AFM produced pictures the scientific evidence behind this controversy is also explained.

Large area Schottky diodes of ZnO films fabricated on platinum layer by pulsed-laser deposition

Large area Schottky diode with novel inverted vertical metal–semiconductor–metal type of structure (Pt/Ti/ZnO/Pt/SiO2/Si) was demonstrated. The effects of crystallinity and native defects of ZnO films on the performance of Schottky diodes were investigated. Through oxygen plasma and post-annealing, the barrier height of Schottky diodes was dramatically enhanced, and the reverse leakage current was reduced by over six orders of magnitude. The obtained Schottky diodes with best performance of Schottky rectification exhibit the barrier height of 0.88 eV, and low reverse leakage current of 4.25 × 10−8 A cm−2 under reverse bias voltage of −2 V. The novel structure was promising for the application of high performance opt-electrical devices.

Dependency of barrier height and ideality factor on identically produced small Au/p-Si Schottky barrier diodes

Small high-quality Au/p-Si Schottky barrier diodes (SBDs) with extremely low reverse leakage current using wet lithography were produced. Their effective barrier heights (BHs) and ideality factors from current–voltage ( I– V) characteristics were measured by a conducting probe atomic force microscope (C-AFM). In spite of identical preparation of the diodes there was a diode-to-diode variation in ideality factor and barrier height parameters. By extrapolating the plots the built-in potential of the Au/p-Si contact was obtained as V bi =0.5425 V and the barrier height value ( Φ B( C− V) ) was calculated to be Φ B( C− V) =0.7145 V for Au/p-Si for a typical 100 μm diode diameters. In the present work the nonlinear dependency of BH and ideality factor on the diode diameter studied fundamentally and an experimental relation for this new behavior is derived. It is found that for the diodes with diameters smaller than 100 μm the diode barrier height and ideality factor dependency to their diameters and correlation between the diode barrier height and its ideality factor are nonlinear, which is similar to the earlier reported different metal semiconductor diodes in the literature, these parameters for the here manufactured diodes with diameters more than 100 μm are also linear. Based on the very obvious sub-nanometer C-AFM produced pictures, the scientific evidence behind this controversy is also explained.

π-Conjugated polymer/GaN Schottky solar cells

We developed heterojunction-based Schottky solar cells consisting of π-conjugated polymers and n-type GaN. Poly (3,4-ethylendioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) was used as the transparent Schottky contact material and their electrical properties were investigated in comparison with those of a polyaniline (PANI) Schottky contact. The PEDOT:PSS/n-GaN/sapphire (0 0 0 1) sample exhibited high-quality rectifying characteristics with a low reverse leakage current of less than 10 −8 A/cm 2 at a reverse bias voltage of −3 V. While investigating the photovoltaic performance, it was observed that the open-circuit voltage of the PEDOT:PSS/n-GaN/sapphire (0 0 0 1) sample reached 0.8 V, which was much superior to the photovoltage reported for a conventional metal/GaN Schottky photodetector. We also confirmed that the PEDOT:PSS is as promising a material as PANI for π-conjugated polymer/GaN Schottky solar cells.

Selective Epitaxial Growth of Silicon Layer Using Batch-Type Equipment for Vertical Diode Application to Next Generation Memories

Vertical diodes for cross-point phase change memory were realized by selective epitaxial growth (SEG) technique using cyclic chemical vapor deposition method. H2/SiH4/Cl2 cyclic CVD system was introduced in batch-type vertical furnace equipement, replacing conventional single-wafer H2/dichlorosilane/HCl CVD system. It provided excellent capacity of 40 wafers per batch. Selectivity loss which is one of the most crucial features in SEG process for diode application was controlled with both the amount of SiH4 and Cl2 and the period of gas supply, and practical value of selectivity loss was confirmed to be less than 100 in 200-mm wafers. Structural and electrical properties of pn diodes were investigated, and cyclic SEG silicon diode showed more eligible electrical ability to current flow than that of poly-si in terms of forward current and ideality factor as well as lower reverse leakage current.

Growth and characteristics of GaInN/GaInN multiple quantum well light-emitting diodes

We demonstrate GaInN multiple quantum well (MQW) light-emitting diodes (LEDs) having ternary GaInN quantum barriers (QBs) instead of conventional binary GaN QBs for a reduced polarization mismatch between QWs and QBs and an additional separate confinement of carriers to the MQW active region. In comparison with GaInN LEDs with conventional GaN QBs, the GaInN/GaInN LEDs show a reduced blueshift of the peak wavelength with increasing injection current and a reduced forward voltage. In addition, we investigate the density of pits emerging on top of the MQW layer that are correlated with V-defects and act as a path for the reverse leakage current. The GaInN/GaInN MQW structure has a lower pit density than the GaInN/GaN MQW structure as well as a lower reverse leakage current. Finally, the GaInN/GaInN MQW LEDs show higher light output power and external quantum efficiency at high injection currents compared to the conventional GaInN/GaN MQW LEDs. We attribute these results to the reduced polarization mismatch and the reduced lattice mismatch in the GaInN/GaInN MQW active region.

Dislocation Clustering and Luminescence Nonuniformity in Bulk GaN and Its Homoepitaxial Film

Cathodoluminescence (CL) spectroscopy and mapping techniques were used to study defect and impurity distributions in free-standing bulk GaN substrates prepared by hydride vapor-phase epitaxy. It was found that, in the bulk GaN substrates investigated, dislocation clusters appearing as dark cores in the CL map were surrounded by bright disk-like regions with higher luminescence efficiency than that of the outside areas. This large-area luminescence nonuniformity disappeared in homoepitaxial GaN grown on top of the GaN substrate. Schottky barrier diodes fabricated on the homo-epilayer exhibited low average reverse leakage current, while dislocation clusters duplicated from the original bulk GaN substrate still limited device yield.

Biosensors using the Si nanochannel junction-isolated from the Si bulk substrate

The biosensor using a silicon nanochannel field effect transistor has been developed on the basis of a bulk silicon substrate instead of an expensive silicon-on-insulator material, for low cost applications. “Top-down” fabricated Si nanochannels for detecting prostate specific antigen (PSA) are electrically isolated from the bulk Si substrate only by a reverse-biased p-n junction with very low reverse leakage currents. The reverse leakage current flowing through the p-n junction is small enough to be ignored, when compared with the current flowing through the p-type Si channel; roughly 100 times lower. The surface immobilization of anti-PSA has been confirmed by the specific binding test of DNA stabilized Au nanoparticles (NPs), showing 1200 NPs/μm2 and atomic force microscopy surface analysis. The injection of 10 ng/ml PSA solutions leads to a clear increase in the conductance of Si nanochannels, indicating the specific binding of PSA with the immobilized anti-PSA. The similar signal changes were observed on the injection of the 1 pg/ml PSA, very low concentration of PSA.

Direct Heteroepitaxy of Vertical InAs Nanowires on Si Substrates for Broad Band Photovoltaics and Photodetection

Catalyst-free, direct heteroepitaxial growth of vertical InAs nanowires on Si(111) substrates was accomplished over a large area by metal-organic chemical vapor deposition. Nanowires showed very uniform diameters and a zinc blende crystal structure. The heterojunctions formed at the interface between the n-type InAs nanowires and the p-type Si substrate were exploited to fabricate vertical array photodiode devices which showed an excellent rectification ratio and low reverse leakage current. Temperature-dependent current transport across the heterojunctions was studied theoretically and experimentally in the dark and under AM 1.5 illumination. When operated in photovoltaic mode, the open-circuit voltage was found to increase linearly with decreasing temperature while the energy conversion efficiency changed nonmonotonically with a maximum of 2.5% at 110 K. Modeling of the nanowire/substrate heterojunctions showed good agreement with the experimental observations, and allowed determining the conduction band offset between the InAs nanowires and Si to be 0.10-0.15 eV. The external quantum efficiency and photoresponsivity profiles of the device showed a broad spectral response from the visible to the infrared region, indicating potential applications as a broad band photovoltaic cell or a visible-infrared dual-band photodetector.

Inhomogeneous Ni/Ge Schottky barriers due to variation in Fermi-level pinning

To achieve high performance Ge nMOSFETs it is necessary to reduce the metal/semiconductor Schottky barrier heights at the source and drain. Ni/Ge and NiGe/Ge Schottky barriers are fabricated by electrodeposition using n-type Ge substrates. Current ( I)–voltage ( V) and capacitance ( C)–voltage ( V) and low temperature I– V measurements are presented. A high-quality Schottky barrier with extremely low reverse leakage current is revealed. The results are shown to fit an inhomogeneous barrier model for thermionic emission over a Schottky barrier. A mean value of 0.57 eV and a standard deviation of 52 meV is obtained for the Schottky barrier height at room temperature. A likely explanation for the distribution of the Schottky barrier height is the spatial variation of the metal induced gap states at the Ge surface due to a variation in interfacial oxide thickness, which de-pins the Fermi level.

Recent Progress of Diamond Device toward Power Application

Diamond is nominated as a material candidate for future high power device due to its superior material properties and resulting very high FOM. In this paper, our recent progresses and the expected possibilities of diamond for power electronics applications are introduced as short review. Firstly for the epitaxial growth, by adopting step-flow epitaxial growth by off- angle substrate with optimized growth conditions, we have succeeded in reducing these killer defects almost six orders from 106cm-2 to almost 100cm-2 levels. For the substrate, our recently developed technology to fabricate diamond plates from bulk, 12x13mm2 size are available to use, that can avoid fabrication difficulties with small size substrate. Secondly for the device, primitive studies showed possibly for the advantage of diamond such as low reverse leakage current, high temperature and high current density operation.

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.

AlGaAs diodes for X-ray spectroscopy

Al 0.8Ga 0.2As p +–p −–n + diodes with low reverse leakage currents (<10 nA) were evaluated as room temperature (23 °C), soft X-ray photon-counting detectors. X-ray spectra from a 55Fe radioactive source show these diodes can be used for spectroscopy with promising energy resolution of 1.47 keV FWHM at 5.9 keV. At elevated reverse bias levels (>20 V), we observed avalanche multiplication which, while improving the signal-to-noise ratio, degraded the spectroscopic performance.

Fabrication and Characterization of Carbon Nanotubes Integrated on Field-Emission Diode

Carbon nanotubes (CNTs) deposited by electrophoresis on a free-standing thin metal film edge are demonstrated. These CNTs act as electron field emitter which was integrated on the cathode of the field-emission vacuum diode. This diode exhibits a low reverse leakage current (<10-11) with high on-off ratio of 106. Owing to the low turn-on voltage of the nanosized CNTs, the field-emission diode exhibited less power consumption compared with the conventional vacuum-tube diode. Electronic tests of this vacuum diode perform its fast switching speed ability and high voltage rectification. This approach presents a route to use nanomaterials with a microelectromechanical system process to develop high-speed vacuum microelectronics.

Fabrication and Characterization of MOVPE-Grown CdTe-on-Si Heterojunction Diode-Type Gamma-Ray Detectors

We report on the growth of very thick (>260 μm) high-crystalline-quality single-crystal CdTe epitaxial films on (211) Si substrates in a metalorganic vapor-phase epitaxy reactor, and the development of gamma ray detectors and their radiation detection properties. Films were grown with a high growth rate varying from 40 μm/h to 70 μm/h. A heterojunction diode was fabricated by growing a 90-μm-thick CdTe layer on an n+-Si substrate, which exhibited good rectifying behavior and had a low reverse bias leakage current of 0.18 μA/cm2 at 100 V bias. The diode clearly demonstrated its gamma radiation detection capability by resolving energy peaks from the 241Am radioisotope during room-temperature measurements. By cooling the diode detector to −30°C, the leakage current could be reduced by three orders of magnitude from the room-temperature value. At this operating condition dramatic improvements in the pulse height spectrum were observed.

Fabrication and passivation of GaSb photodiodes

A novel Zn diffusion technique in n-GaSb substrate from a low temperature chemical bath deposited ZnS layer has been developed to obtain high breakdown voltages. Junctions formed by this technique have breakdown voltages of ∼18.5V, low reverse leakage current (0.01–0.03A/cm2 at -3V), excellent reverse current saturation and ideality factor of ∼1.3. The high breakdown voltages obtained are due to the co-doping of zinc and sulfur from the ZnS film. Sulfur forms shallow and deep levels that compensate the p-doping of zinc. The non-linear relation of the inverse of the zero-bias resistance area product (1/R0A) versus perimeter to area ratio (P/A) in these diodes indicates surface leakage is the dominant leakage mechanism. CdS has been used to passivate the mesa photodiodes. After passivation, the 1/R0A product reduces from 0.3 to 0.02Ω-1cm-2 for a 150μm diameter device. The 1/R0A product is also independent of the diode dimension confirming effective passivation. ZnS surface passivation on the mesa walls is not effective and is found to increase the leakage current.

Characteristics of Green Light-Emitting Diodes Using an InGaN:Mg/GaN:Mg Superlattice as p-Type Hole Injection and Contact Layers

Mg-doped InGaN/GaN p-type short-period superlattices (SPSLs) are developed for hole injection and contact layers of green light-emitting diodes (LEDs). V-defect-related pits, which are commonly found in an InGaN bulk layer, can be eliminated in an InGaN/GaN superlattice with thickness and average composition comparable to those of the bulk InGaN layer. Mg-doped InGaN/GaN SPSLs show significantly improved electrical properties with resistivity as low as ∼0.35 ohm-cm, which is lower than that of GaN:Mg and InGaN:Mg bulk layers grown under optimized growth conditions. Green LEDs employing Mg-doped InGaN/GaN SPSLs for hole injection and contact layers have significantly lower reverse leakage current, which is considered to be attributed to improved surface morphology. The peak electroluminescence intensity of LEDs with a SPSL is compared to that with InGaN:Mg bulk hole injection and contact layers.

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 &amp;lt;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.

High-Performance Poly-Ge Thin-Film Transistor with NiGe Schottky Source/Drain

High-performance poly-Ge thin-film transistors (TFTs) were fabricated using NiGe Schottky contacts as source/drain (S/D). First, formation of NiGe layers by annealing of Ni/n-Ge structures was investigated as a function of annealing temperature, and NiGe/n-Ge Schottky contacts (Φ Bn =0.51 eV) with a low reverse leakage current (∼10 -2 A/cm 2 ) were realized at 200-300°C. On the basis of the results, NiGe Schottky S/D contacts were fabricated using poly-Ge/quartz substrates. The TFTs showed good operation characteristics with a hole mobility of ∼140cm 2 V 1 s 1 . This is a great advantage for the realization of high-performance TFTs for future system-in-displays.

Analysis of thermionic emission from electrodeposited Ni–Si Schottky barriers

Ni–Si Schottky barriers are fabricated by electrodeposition using n on n + Si substrates. I – V , C – V and low temperature I – V measurements are presented. A high-quality Schottky barrier with extremely low reverse leakage current is revealed. The results are shown to fit an inhomogeneous barrier model for thermionic emission over a Schottky barrier proposed by Werner and Guttler [J.H. Werner, H.H. Guttler, Barrier inhomogeneities at Schottky contacts, J. Appl. Phys. 69 (3) (1991) 1522–1533]. A mean value of 0.76 V and a standard deviation of 66 mV is obtained for the Schottky barrier height at room temperature with a linear bias dependence. X-ray diffraction and scanning electron microscopy measurements reveal a polycrystalline Ni film with grains that span from the Ni–Si interface to the top of the Ni layer. The variation in Ni orientation is suggested as a possible source of the spatial distribution of the Schottky barrier height.