Effective Schottky Barrier Research Articles

Electromechanical Characterization of Single GaN Nanobelt Probed with Conductive Atomic Force Microscope

The electromechanical characterization of the field effect transistor based on a single GaN nanobelt was performed under different loading forces by using a conductive atomic force microscope (C-AFM), and the effective Schottky barrier height (SBH) and ideality factor are simulated by the thermionic emission model. From 2-D current image, the high value of the current always appears on the nanobelt edge with the increase of the loading force less than 15 nN. The localized (I–V) characteristic reveals a typical rectifying property, and the current significantly increases with the loading force at the range of 10–190 nN. The ideality factor is simulated as 9.8 within the scope of GaN nano-Schottky diode unity (6.5–18), therefore the thermionic emission current is dominant in the electrical transport of the GaN-tip Schottky junction. The SBH is changed through the piezoelectric effect induced by the loading force, and it is attributed to the enhanced current. Furthermore, a single GaN nanobelt has a high mechanical-induced current ratio that could be made use of in a nanoelectromechanical switch.

Surface plasmon-driven photoelectrochemical water splitting of aligned ZnO nanorod arrays decorated with loading-controllable Au nanoparticles

In this paper, we designed a series of well-aligned ZnO nanorod arrays decorated with loading-controllable Au nanoparticles and studied their surface plasmon-driven photoelectrochemical (PEC) water splitting performances. The PEC water splitting ability of Au-ZnO nanorod arrays was evaluated under illumination with λ > 420 nm light. These nanorod arrays show remarkable PEC water splitting performances and achieve the highest photocurrent density of 30 μA cm−2 at 0.8 V versus Ag/AgCl. Furthermore, the PEC performance for heterogenous nanorod arrays can be effectively adjusted by controlling loading amounts of Au nanoparticles. We experimentally demonstrate that the Au-ZnO nanorod arrays show enhanced visible light absorption ability. The superior PEC performance of Au-ZnO nanorod arrays is attributed to the synergistic effects of plasmonic Au nanoparticles, ZnO semiconductor and Schottky barrier built in heterogenous nanorod array. This work provides a facile strategy to manipulate the PEC water splitting activity of Au-ZnO hybrid nanostructures by simply controlling the loading amounts of metallic Au nanoparticles. Furthermore, our research offers a potentially efficient strategy for the design and fabrication of new types of plasmonic-metal/semiconductor hybrid nanostructures with a plasmonic-enhanced PEC water splitting activity under the visible light, which are as valuable photocatalysts for solar-to-chemical/electrical energy conversion.

Gate Tunable Self-Biased Diode Based on Few Layered MoS2 and WSe2

The operation of a self-biased diode (SBD) based on MoS2 has been demonstrated by using an asymmetric top gate comprising metal-hexagonal boron nitride (h-BN)-MoS2 structure. The rectification is achieved by asymmetric modulation of effective Schottky barrier and carrier density in the channel during forward and reverse bias, and a rectification factor of 1.3 × 105 is achieved in I–V characteristics. The modulation of effective Schottky barrier is verified by temperature dependent measurement in a range of 173 to 373 K, and a difference of 300 meV is observed in effective Schottky barrier height for forward and reverse bias. The electrical characteristics of SBD exhibit close resemblance with an ideal thermionic emission model with an ideality factor of 1.3. SBD also exhibits strong photoelectrical response with a specific detectivity of 150 A/W and responsivity of 2.1 × 1010 Jones under 450 nm laser light illumination. In the end, to demonstrate the diversity of the proposed scheme, SBD based on WSe2 has...

Improved Ohmic Contact by Pre‐Metallization Annealing Process in Quaternary In0.04Al0.65Ga0.31N/GaN HEMTs

We report on the performance improvement of ohmic contact by a pre‐metallization annealing process after mesa‐isolation in quaternary InAlGaN/GaN high electron mobility transistors (HEMTs). By employing a pre‐metallization annealing, the contact and specific contact resistances are improved from 0.31 Ω · mm and 3.67 × 10−6 Ω cm2 to 0.21 Ω mm and 1.63 × 10−6 Ω cm2, respectively. The angle‐resolved X‐ray photoelectron spectroscopy (AR‐XPS) confirm the formation of nitrogen vacancies from the reduced atomic ratio of nitrogen and the binding energy shift of In3d5/2, Al2p1/2, and Ga2p3/2 toward the higher energy after the pre‐metallization annealing. Nitrogen vacancies that act as n‐type dopants make the effective Schottky barrier thinner leading to the improved contact resistance. When the pre‐metallization annealing process is employed to fabricate 200‐nm‐long gate HEMTs, the on‐resistance and the maximum transconductance are improved from 1.7 Ω mm and 400 mS mm−1 to 1.0 Ω mm and 618 mS mm−1, respectively.

Investigation of Schottky Barrier, Conventional and Tunnel Carbon Nanotube Field Effect Transistor for Low Power Design

Investigation of Schottky Barrier, Conventional and Tunnel Carbon Nanotube Field Effect Transistor for Low Power Design

Silicon carbide of Ni/6H-SiC and Ti/4H-SiC type Schottky diode current-voltage characteristics modelling

On the base of the physical analytical models based on Poisson’s equation, drift–diffusion and continuity equations the forward current–voltage characteristics of 6H-SiC and 4H-SiC type Schottky diode with Ni and Ti Schottky contact have been simulated. It is shown on the base of analysis of current–voltage characteristics in terms of classical thermionic emission theory it is shown that the proposed simulation model of Schottky diode corresponds to the almost “ideal” diode with ideality factor n equals 1.1. Because of this it is determined that the effective Schottky barrier height φB equals 1.57 eV and 1.17 eV for Ni/6H and Ti/4H silicon carbide Schottky diode type, respectively.

Exploring the Charge Transport in Conjugated Polymers.

Conjugated polymers came to an unprecedented epoch that the charge transport is limited only by small disorder within aggregated domains. Accurate evaluation of transport performance is thus vital to optimizing further molecule design. Yet, the routine method by means of the conventional field-effect transistors may not satisfy such a requirement. Here, it is shown that the extrinsic effects of Schottky barrier, access transport through semiconductor bulk, and concurrent ambipolar conduction seriously influence transport analysis. The planar transistors incorporating ohmic contacts free of access and ambipolar conduction afford an ideal access to charge transport. It is found, however, that only the planar transistors operating in low-field regime are reliable to explore the inherent transport properties due to the energetic disorder lowering by the lateral field induced by high drain voltage. This work opens up a robust approach to comprehend the delicate charge transport in conjugated polymers so as to develop high-performance semiconducting polymers for promising plastic electronics.

Modulation of Minority Carriers in the C-V Characteristics of MIS Tunneling Diode by Surrounding MOS Capacitor

In this work, the capacitance-voltage (C-V) and current-voltage (I-V) measurements on the metal-insulator-semiconductor tunnel diode (MIS TD) with or without surrounding metal-oxide-semiconductor (MOS) capacitor were presented. The different C-V and I-V characteristics of the MIS TD observed between the two devices suggests that the minority carrier concentration in substrate surface of the MIS TD could be affected by the gate bias of the surrounding MOS capacitor, which modulates the effective Schottky barrier height and reverse-biased current of the MIS TD.

High-Density and Near-Linear Synaptic Device Based on a Reconfigurable Gated Schottky Diode

A reconfigurable gated Schottky diode is proposed as new high-density and low-power synaptic device that has near-linear changes in conductance. The device has a reverse current of less than 12 nA/ $\mu \text{m}$ and an effective device area of 6F2. Since the Al/poly-Si Schottky junction is located on the bottom gate, which has a SiO2/Si3N4/SiO2 charge trap layer, the effective Schottky barrier height is modulated by the bottom gate bias or by the amount of charge trapped in the Si3N4 layer. The Schottky reverse current has an exponential relationship with the effective Schottky barrier height associated with the amount of stored charge, and the amount of stored charge is logarithmically proportional to the number of potentiation pulses. Because the exponential and logarithmic relationships cancel each other out, a near-linear conductance response to the number of potentiation pulses is obtained from the proposed device.

Electrical and interface properties of PdAl/Au metal alloyed ohmic contacts on p-type GaN for high-temperature MEMS devices

In this work, a PdAl/Au (20/30 nm) metal alloyed scheme was investigated for obtaining low resistance ohmic contacts to Mg-doped p-type GaN. The specific contact resistance (ρSCR) was determined using the circular-transmission-line pattern method between the metal contacts and p-type GaN by current–voltage (I–V) measurements. It is noted that the ρSCR of the as-deposited contact (1.23 × 10−2 Ω cm2) was enhanced upon rapid thermal annealing (RTA) at 600 °C (7.82 × 10−4 Ω cm2) for 1 min under N2 ambient. The effective Schottky barrier heights (SBHs) of the various annealed contacts were determined using the Norde and I–V methods. It is observed that the effective SBHs were dependent upon the RTA conditions. According to the X-ray diffraction and X-ray photoelectron spectroscopy results, the gallide-related phases were formed at the PdAl/Au/p-GaN interface such as Au7Ga2 and Ga3Pd5 upon RTA at 600 °C. These phases were responsible for obtaining low contact resistivity of the PdAl/Au contact. Atomic force microscopy results show that the surface morphology (root-mean-square, RMS) of the contact was reasonably smooth even after RTA at 600 °C with an RMS roughness of 0.714 nm. Observations indicate that the PdAl/Au metal alloyed contact was a suitable ohmic contact to p-type GaN for the development of commercially viable large-scale GaN-based microelectromechanical system applications.

A self-adjusting mechanism of schottky junction constructed by zero-bandgap graphene for highly efficient electrochemical biosensing

Constructing schottky junction with zero-bandgap graphene was innovatively achieved by electrochemical reduction and deposition of GO on NiO foam directly. The fabricated 3D graphene/NiO foam exhibited highly efficient sensing performance towards positively charged dopamine molecules. The main mechanism is that the adsorbate-induced charges could change the schottky barrier height, following by selectively enhancing or depressing the electrochemical responses of different charged analytes. The proposed self-adjusting effects of schottky barrier on electrochemical signals were theoretically and experimentally explored in depth. As a result, it can help to break the limitation that analytes with similar redox properties are difficult to distinguish by electrochemical methods

Influence of Asymmetric Contact Form on Contact Resistance and Schottky Barrier, and Corresponding Applications of Diode.

We have fabricated carbon nanotube and MoS2 field-effect transistors with asymmetric contact forms of source-drain electrodes, from which we found the current directionality of the devices and different contact resistances under the two current directions. By designing various structures, we can conclude that the asymmetric electrical performance was caused by the difference in the effective Schottky barrier height (ΦSB) caused by the different contact forms. A detailed temperature-dependent study was used to extract and compare the ΦSB for both contact forms of CNT and MoS2 devices; we found that the ΦSB for the metal-on-semiconductor form was much lower than that of the semiconductor-on-metal form and is suitable for all p-type, n-type, or ambipolar semiconductors. This conclusion is meaningful with respect to the design and application of nanomaterial electronic devices. Additionally, using the difference in barrier height caused by the contact forms, we have also proposed and fabricated Schottky barrier diodes with a current ratio up to 104; rectifying circuits consisting of these diodes were able to work in a wide frequency range. This design avoided the use of complex chemical doping or heterojunction methods to achieve fundamental diodes that are relatively simple and use only a single material; these may be suitable for future application in nanoelectronic radio frequency or integrated circuits.

A novel electrostatically doped ferroelectric Schottky barrier tunnel FET: process resilient design

This work investigates a process-variation resilient electrostatically-doped ferroelectric Schottky-barrier tunnel FET (ED-FE-SB-TFET) based on negative capacitance (NC). The key attributes of ED-FE-SB-TFET are perovskite ferroelectric (FE) gate stack-induced NC behavior and electrostatic doping to induce pockets at both source/drain and channel interfaces. The positive feedback among the electric dipoles in FE material leads to intrinsic voltage amplification and enhanced gate controllability, thus it facilitates faster switching transitions. The proposed ED-FE-SB-TFET endeavors to create a substantial reduction in the ambipolar current ( $$I_\mathrm{Amb}$$ ), steep sub-threshold slope, paramount boost in drive current, lower drain-induced barrier-lowering, and enhanced scalability. It also obviates the need for metallurgical doping, hence ion-implantation or dopant segregation techniques employed for planar SB-TFETs pocket-doping are no longer required, and it also modifies effective Schottky barrier height and Schottky tunneling barrier width significantly to enhance the device behavior. It offers a simplified fabrication process, and it is highly resilient towards process variations, doping control issues, and random dopant fluctuations. Moreover, there is a reduced thermal budget that facilitates its fabrication on single crystal silicon-on-glass substrate realized by wafer scale epitaxial transfer. Results reveal its potential as strong candidate for next generation, scaled and low power applications.

Forward current-voltage characteristics simulation of 4H-SiC silicon carbide Schottky diode for power electronics

Forward current-voltage characteristics of 4H-SiC Schottky diode with Ni Schottky contact have been simulated based on in the physical analytical models based on Poisson’s equation, drift-diffusion and continuity equations. On the base of analysis of current-voltage characteristics in terms of classical thermionic emission theory it is established that the proposed simulation model of Schottky diode corresponds to the “ideal” diode with average ideality factor n»1.1 at low temperature ~300 K. It is determined that effective Schottky barrier height equals 1.1 eV for Ni/4H-SiC Schottky diode.

Nanocontact Disorder in InP Nanowire Devices for the Enhancement of Visible Light and Oxygen Gas Sensitivities

InP nanowires, synthesized through a self-seeded growth approach, are used in the fabrication of field-effect transistors which consist of source, drain, and back-gate electrodes. The weak gating voltage dependence implies low carrier concentrations whereas its behavior reveals native n-type doping in InP nanowires. These InP nanowire devices exhibit a vast variation of room-temperature resistance that raises a question about contact resistance. For devices of low room-temperature resistance, electron transport in InP nanowires is investigated using temperature dependent resistance in the temperature range between 80 and 300 K, and it can be analyzed using the model of thermal activation. For other devices of high room-temperature resistance, we take into account nanocontact resistance. Models of both Schottky contact and Mott's variable range hopping (VRH) are considered. The two resistances are connected in parallel to give total contact resistance of InP nanowire devices. After fitting experimental data by the proposed model, we estimate effective Schottky barriers and disorder contributions to nanocontact resistance. The effective Schottky barrier, and the nanocontact Schottky and Mott's VRH resistances are plotted as a function of the device room-temperature resistance which indicates the scale of disorder. Using room-temperature resistance of InP nanowire devices, the devices are classified into nanowire- or contact-dominated devices. The two different class of devices are used to check their photo- and gas-sensitivities. The contact-dominated InP nanowire devices show low dark current and low photocurrent as usual, but these contact-dominated devices give high ratio of photo- to dark-current. That result reveals a high photo-sensitivity for those devices of high nanocontact resistance. On the other hand, for gas sensing experiments, the contact-dominated devices show as well a high ratio of resistance under O2 to that under N2 gas exposure.

Role of fringing field on the electrical characteristics of metal-oxide-semiconductor capacitors with co-planar and edge-removed oxides

Due to the simplicity of the fabrication process, the ultra-thin oxide metal-oxide-semiconductor capacitors (MOSCAPs) can be a promising device for sensing, memory, and transconductance applications. The investigation of the fundamental electrical characteristics of ultra-thin oxide MOSCAPs is still of importance. In this work, the influence of the removal of the surrounded gate oxide was studied to know the role of fringing field. For edge-removed oxide, the tunneling saturation current shows no oxide thickness dependency and exhibits a low current level of 9.4×10−11 at 2V (dox=2.3 nm). Also, its deep depletion occurs earlier when biasing. In contrast, for the device without oxide removing, i.e., co-planar oxide, the saturation current is strongly related to the oxide thickness and exhibits a high current level of 3.5×10−6 at 2V (dox=2.3 nm) due to regular oxide voltage drop modulation effect on effective Schottky barrier height. For the thick oxide of 4.2 nm the inversion capacitances are frequency dependant for CP-OX but are independent for ER-OX MOSCAPs. These characteristics are mainly caused by the different fringing fields and the defect densities at device edge between two structures.

Evidence of minority carrier traps contribution in deep level transient spectroscopy measurement in n–GaN Schottky diode

It is shown that deep level transient spectroscopy can be carried out on Schottky diodes to investigate, in addition to majority carrier traps, minority carrier traps. This is possible thanks to the application of a large reverse bias to the device which allows minority carrier injection by lowering their corresponding effective Schottky barrier height. Indeed, when increasing the reverse bias voltage, the deep level transient spectroscopy signal, initially negative and thus showing only majority carrier traps signature, becomes positive, revealing minority carrier traps involvement. A careful analysis of the recorded spectra leads to the identification of four minority carrier traps which have been so far only evidenced using dedicated technique such as minority carrier transient spectroscopy.

Electrical Transport Properties of Au Nanoparticles and Thin Films on Ge Probed Using a Conducting Atomic Force Microscope.

In this work, gold nanoparticles (Au NPs) were distributed on an n-Ge substrate using the colloidal NP deposition method to form Au NP/Ge Schottky diodes (SDs), and the current transport properties of these nano-SDs were studied. The current density-voltage (J-V) characteristics were measured on each nanometer-sized Au particle using a conducting atomic force microscope (C-AFM). These Au NP/Ge diodes showed a rectifying behavior. According to the thermionic emission (TE) model, the effective Schottky barrier height (SBH) and ideality factors n were obtained. The SBH for the Au NP/Ge diodes ranges from 0.22 to 0.30 eV and the ideality factor ranges from 3.8 to 8.6. The current density and the barrier height increase while the ideality factor decreases with increasing Au NP diameters. This indicates that the tunneling effect is enhanced because of the narrowed depletion width and decreased size of the Au NP/Ge SDs. To compare the electrical behavior with Au NP/Ge diodes, the Au thin film/Ge diodes were also prepared and their SBHs were much larger because of the image-charge lowering effect and the tunneling effect in Au NP/Ge diodes.

Electron Excess Doping and Effective Schottky Barrier Reduction on the MoS2/h-BN Heterostructure.

Layered hexagonal boron nitride (h-BN) thin film is a dielectric that surpasses carrier mobility by reducing charge scattering with silicon oxide in diverse electronics formed with graphene and transition metal dichalcogenides. However, the h-BN effect on electron doping concentration and Schottky barrier is little known. Here, we report that use of h-BN thin film as a substrate for monolayer MoS2 can induce ∼6.5 × 1011 cm-2 electron doping at room temperature which was determined using theoretical flat band model and interface trap density. The saturated excess electron concentration of MoS2 on h-BN was found to be ∼5 × 1013 cm-2 at high temperature and was significantly reduced at low temperature. Further, the inserted h-BN enables us to reduce the Coulombic charge scattering in MoS2/h-BN and lower the effective Schottky barrier height by a factor of 3, which gives rise to four times enhanced the field-effect carrier mobility and an emergence of metal-insulator transition at a much lower charge density of ∼1.0 × 1012 cm-2 (T = 25 K). The reduced effective Schottky barrier height in MoS2/h-BN is attributed to the decreased effective work function of MoS2 arisen from h-BN induced n-doping and the reduced effective metal work function due to dipole moments originated from fixed charges in SiO2.

Electrical properties of Ge crystals and effective Schottky barrier height of NiGe/Ge junctions modified by P and chalcogen (S, Se, or Te) co-doping

The electrical properties of Ge crystals and the effective Schottky barrier height (SBH) of NiGe/Ge diodes fabricated by P and/or chalcogen (S, Se, or Te) doping were investigated for Ge n-channel metal–oxide–semiconductor field-effect transistors with a NiGe/n+Ge junction. The electron concentration in Ge was increased more by co-doping with chalcogen and P than by doping with P alone. Moreover, SBH values were decreased in NiGe/nGe diodes and increased in NiGe/pGe diodes compared with undoped NiGe/Ge by both P doping and P and chalcogen co-doping. Co-doping with Te and P was most effective in modifying the SBH.