Showing papers on "Schottky diode published in 2012"

Field-effect transistors and intrinsic mobility in ultra-thin MoSe2 layers

Abstract: We report the fabrication of back-gated field-effect transistors (FETs) using ultra-thin, mechanically exfoliated MoSe2 flakes. The MoSe2 FETs are n-type and possess a high gate modulation, with On/Off ratios larger than 106. The devices show asymmetric characteristics upon swapping the source and drain, a finding explained by the presence of Schottky barriers at the metal contact/MoSe2 interface. Using four-point, back-gated devices, we measure the intrinsic conductivity and mobility of MoSe2 as a function of gate bias, and temperature. Samples with a room temperature mobility of ∼ 50 cm2/V·s show a strong temperature dependence, suggesting phonons are a dominant scattering mechanism.

Field-effect transistors and intrinsic mobility in ultra-thin MoSe2 layers

Abstract: We report the fabrication of back-gated field-effect transistors (FETs) using ultra-thin, mechanically exfoliated MoSe2 flakes. The MoSe2 FETs are n-type and possess a high gate modulation, with On/Off ratios larger than 106. The devices show asymmetric characteristics upon swapping the source and drain, a finding explained by the presence of Schottky barriers at the metal contact/MoSe2 interface. Using four-point, back-gated devices we measure the intrinsic conductivity and mobility of MoSe2 as a function of gate bias, and temperature. Samples with a room temperature mobility of ~50 cm2/V.s show a strong temperature dependence, suggesting phonons are a dominant scattering mechanism.

Metal--Semiconductor Schottky Barrier Junctions and Their Applications

Abstract: 1. Physics of Schottky Barrier Junctions.- 1. Introduction.- 2. Origins of Barrier Height.- 2.1. Schottky-Mott Theory of Ideal Metal-Semiconductor Contact.- 2.2. Modifications to Schottky Theory.- 2.3. Classifications of Metal-Semiconductor Interfaces.- 2.4. Contacts on Reactive Interfaces.- 2.5. Contacts with Surface States and an Insulating Interfacial Layer.- 2.6. Contacts on Vacuum Cleaved Surfaces.- 3. Measurement of Barrier Height.- 3.1. Capacitance-Voltage Measurement.- 3.2. Current-Voltage Measurement.- 3.3. Photoelectric Measurement.- 4. Results of Barrier Height Measurements.- 4.1. Chemically Prepared Surfaces.- 4.2. Vacuum Cleaved Surfaces.- 4.3. Concluding Remarks.- 5. Capacitance-Voltage Characteristics.- 5.1. Electric Field and Potential Distribution in the Depletion Region.- 5.2. Depletion Region Capacitance.- 5.2.1. Ideal Schottky Barrier.- 5.2.2. Effect of Minority Carriers.- 5.2.3. Effect of Interfacial Layer.- 5.2.4. Effect of Deep Traps.- 6. Current-Voltage Characteristics.- 6.1. Transport Mechanisms.- 6.1.1. Diffusion and Thermionic Emission over the Barrier.- 6.1.2. Tunneling through the Barrier.- 6.1.3. Carrier Generation and Recombination in the Junction Depletion Region.- 6.1.4. Minority Carrier Injection.- 6.2. Forward Characteristics.- 6.3. Reverse Characteristics.- 7. Transient Behavior.- 8. Low-Resistance Schottky Barrier Contacts.- References.- 2. Interface Chemistry and Structure of Schottky Barrier Formation.- 1. Introduction.- 2. Perspectives on Schottky Barrier Formation.- 2.1. Introduction.- 2.2. Brief Review of Phenomenological Schottky Barrier Data.- 3. The Chemistry and Structure of the Interfacial Layer.- 3.1. Synopsis of the Layer-by-Layer Evolution.- 3.2. Some Techniques for Studying the Stages of Interface Formation.- 4. Evolution of the Interfacial Layer.- 4.1. Stage 0: The Clean Semiconductor Surface.- 4.1.1. Silicon (100) and (111) Surfaces.- 4.1.2. GaAs (110) and GaAs (100) Surfaces.- 4.2. Stage 1: The Dilute Limit (< 1/2 Monolayer).- 4.3. Stage 2: Monolayer Formation-Metal Film Nucleation.- 4.4. Stage 3: Additional Monolayers and Interdiffusion.- 4.5. Some Specific Characteristics of the Interfacial Layers.- 5. Formation of Interface States.- 5.1. Intrinsic Interface States Derived from the Metal and Semiconductor.- 5.2. Localized Defect and Impurity Related States.- 5.3. Interface States and the Stages of Interface Formation.- 6. Case Studies of the Chemistry and Structure of Schottky Barrier Formation.- 6.1. Case Studies of Silicon Schottky Barriers.- 6.1.1. Al, Ag, Cu, and Au Schottky Barriers.- 6.1.2. Silicide-Silicon Interfaces.- 6.2. Case Studies of III-V and II-VI Compound Semiconductor Schottky Barriers.- 6.2.1. The Ga-Al-As System.- 6.2.2. The GaAlAs Ternary System with Au Schottky Barriers.- 6.2.3. InP.- 6.2.4. Some II-VI Examples.- 7. Summary.- References.- 3. Fabrication and Characterization of Metal-Semiconductor Schottky Barrier Junctions.- 1. Introduction.- 2. Selection of Semiconductor Materials.- 3. Metal-Semiconductor Systems.- 3.1. Metal-Silicon Systems.- 3.2. Metal-GaAs Systems.- 3.3. Multilayer Metallization Systems.- 4. Design Considerations.- 5. Fabrication Technology.- 5.1. Surface Processing.- 5.2. Dielectric Film Deposition.- 5.3. Ohmic Contact Formation.- 5.4. Metal Deposition.- 5.5. Other Steps.- 6. Characterization.- References.- 4. Schottky-Barrier-Type Optoelectronic Structures.- 1. Introduction.- 2. Barrier Formation in Schottky-Barrier-Type Junctions.- 3. Transport in Schottky-Barrier-Type Structures.- 3.1. MS and MIS Structures.- 3.2. SIS Structures.- 4. Schottky-Barrier-Type Optoelectronic Structures.- 4.1. Schottky-Barrier-Type Light-Emitting Structures.- 4.2. Schottky-Barrier-Type Photodiodes.- 4.3. Schottky-Barrier-Type Photovoltaic Devices.- 4.3.1. MS and MIS Photovoltaic Devices.- 4.3.2. SIS Photovoltaic Devices.- 3. Summary.- References.- 5. Schottky Barrier Photodiodes.- 1. Introduction.- 2. General Parameters of Photodiodes.- 2.1. Signal-to-Noise Ratio (S/N).- 2.2. Noise Equivalent Power (NEP).- 2.3. Detectivity (D).- 2.4. Normalized Detectivity (D*).- 2.5. Detectivity Normalized Also with Respect to the Field of View(D**).- 2.6. Resistance Area Product.- 2.7. Response Time.- 3. Selection of Materials.- 3.1. Metal Systems.- 3.2. Semiconducting Materials.- 4. Fabrication Technology.- 5. Techniques for Evaluating Device Parameters.- 5.1. Current-Voltage Characteristics.- 5.2. Capacitance-Voltage Characteristics.- 5.3. Photoelectric Measurements.- 5.4. Electron Beam Induced Current Technique.- 6. Applications.- 7. Conclusions.- References.- 6. Microwave Schottky Barrier Diodes.- 1. Introduction.- 2. Diode Design Considerations.- 2.1. Equivalent Circuit.- 2.2. Frequency Conversion.- 2.3. Basic Mixer Diode RF Parameters.- 2.3.1. Conversion Loss Theory.- 2.3.2. Noise-Temperature Ratio.- 2.3.3. Overall Receiver Noise Figure.- 2.3.4. Mixer Noise Temperature.- 2.3.5. RF Impedance.- 2.3.6. IF Impedance.- 2.3.7. Receiver Sensitivity.- 2.3.8. Doppler Shift.- 2.3.9. Typical Doppler Radar System.- 2.4. Basic Detector RF Parameters.- 2.4.1. Video Resistance (Rv).- 2.4.2. Voltage Sensitivity.- 2.4.3. Current Sensitivity ?.- 2.4.4. Minimum Detectable Signal (MDS).- 2.4.5. Tangential Signal Sensitivity (TSS).- 2.4.6. Nominal Detectable Signal (NDS).- 2.4.7. Noise Equivalent Power (NEP).- 2.4.8. Video Bandwidth.- 2.4.9. Superheterodyne vs. Single Detection.- 2.5. Mixer Configurations.- 2.5.1. Single-Ended Mixer.- 2.5.2. Single-Balanced Mixer.- 2.5.3. Double-Balanced Mixer.- 2.5.4. Image Rejection Mixer.- 2.5.5. Image Enhanced or Image Recovery Mixer.- 3. Properties of Schottky Barrier Diodes.- 3.1. Diode Theory.- 3.2. DC Parameters.- 3.2.1. Junction Capacitance.- 3.2.2. Overlay Capacitance.- 3.2.3. Series Resistance.- 3.2.4. Figure of Merit.- 3.3. Semiconductor Materials.- 3.4. Epitaxial GaAs.- 3.5. Barrier Height Lowering.- 3.6. Fabrication.- 4. Microwave Performance.- 4.1. Mixer Diodes.- 4.2. Detector Diodes.- 5. RF Pulse and CW Burnout.- 5.1. Introduction.- 5.2. Factors Affecting RF Burnout.- 5.3. Experimental Results.- 5.4. Physical Analysis of RF Pulsed Silicon Schottky Barrier Failed Diodes.- 5.5. Physical Analysis of RF Pulsed Millimeter GaAs Schottky Barrier Failed Diodes.- 5.6. Electrostatic Failure of Silicon Schottky Barrier Diodes.- 6. Conclusions.- References.- 7. Metal-Semiconductor Field Effect Transistors.- 1. Introduction.- 2. Small-Signal FET Theory.- 3. Design Parameters of a Low-Noise Device.- 4. Practical Small-Signal FET Fabrication Techniques.- 4.1. Material Growth Techniques.- 4.2. FET Fabrication Technology.- 5. GaAs Power Field Effect Transistors.- 5.1. Principle of Power FET Operation.- 5.2. Thermal Impedance.- 5.3. Power FET Technology.- 6. Conclusions.- References.- 8. Schottky Barrier Gate Charge-Coupled Devices.- 1. Introduction.- 2. Schottky Gate CCDs.- 3. Potential-Charge Relationships.- 3.1. Surface Channel CCD.- 3.2. Bulk Channel CCD.- 3.3. Schottky Gate CCD.- 4. Charge Storage Capacity.- 4.1. Surface Channel CCD.- 4.2. Bulk Channel CCD.- 4.3. Schottky Gate CCD.- 5. Charge Transfer.- 5.1. Charge Transfer Efficiency.- 5.2. Charge Transfer Mechanisms.- 5.2.1. Surface Channel CCD.- 5.2.2. Bulk Channel CCD.- 5.2.3. Schottky Gate CCD.- 6. Input-Output Circuits.- 7. Schottky Gate Heterojunction CCDs.- 8. Experimental Results.- 8.1. High-Frequency Devices.- 8.2. Heterojunction Devices.- 9. Applications.- References.- 9. Schottky Barriers on Amorphous Si and their Applications.- 1. Introduction.- 2. Properties of Amorphous Si.- 2.1. Deposition Methods.- 2.2. Structural Properties.- 2.3. Electronic Properties.- 2.4. Surfaces.- 3. The Schottky Barrier on ?-Si:H.- 3.1. Current-Voltage Measurements.- 3.2. Capacitance Measurements.- 3.3 Internal Photoemission.- 4. Interface Kinetics and Its Effect on the Schottky Barrier.- 5. Applications.- 5.1. Drift Mobility.- 5.2. Deep Level Transient Spectroscopy.- 5.3. Solar Cells.- 5.4. Thin Film Transistors.- 6. Concluding Remarks.- References.

Schottky solar cells based on CsSnI3 thin-films

Abstract: We describe a Schottky solar cell based on the perovskite semiconductor CsSnI3 thin-film. The cell consists of a simple layer structure of indium-tin-oxide/CsSnI3/Au/Ti on glass substrate. The measured power conversion efficiency is 0.9%, which is limited by the series and shunt resistance. The influence of light intensity on open-circuit voltage and short-circuit current supports the Schottky solar cell model. Additionally, the spectrally resolved short-circuit current was measured, confirming the unintentionally doped CsSnI3 is of p-type characteristics. The CsSnI3 thin-film was synthesized by alternately depositing layers of SnCl2 and CsI on glass substrate followed by a thermal annealing process.

Opportunity of spinel ferrite materials in nonvolatile memory device applications based on their resistive switching performances.

Abstract: The opportunity of spinel ferrites in nonvolatile memory device applications has been demonstrated by the resistive switching performance characteristics of a Pt/NiFe2O4/Pt structure, such as low operating voltage, high device yield, long retention time (up to 105 s), and good endurance (up to 2.2 × 104 cycles). The dominant conduction mechanisms are Ohmic conduction in the low-resistance state and in the lower-voltage region of the high-resistance state and Schottky emission in the higher-voltage region of the high-resistance state. On the basis of measurements of the temperature dependence of the resistances and magnetic properties in different resistance states, we explain the physical mechanism of resistive switching of Pt/NiFe2O4/Pt devices using the model of formation and rupture of conducting filaments by considering the thermal effect of oxygen vacancies and changes in the valences of cations due to the redox effect.

Low-Power Wireless Power Delivery

Abstract: This paper addresses design and implementation of integrated rectifier-antennas (rectennas) for wireless powering at low incident power densities, from 25 to 200 μW/cm2. Source-pull nonlinear measurement of the rectifying devices is compared to harmonic-balance simulations. Optimal diode RF and dc impedances for most efficient rectification, as a function of input power, are obtained. This allows optimized antenna design, which can eliminate or simplify matching networks and improve overall efficiency. As an example of the design methodology, Schottky diodes were characterized at 1.96 GHz and an antenna is matched to the optimal complex impedance for the most efficient rectifier. For incident power density range of interest, the optimal impedance is 137 + j149 Ω, with an RF to dc conversion efficiency of the rectifying circuit alone of 63% and total rectenna efficiency of 54%.

24 Gbit/s data transmission in 300 GHz band for future terahertz communications

Abstract: Presented is 24 Gbit/s wireless data transmission at 300 GHz using a uni-travelling carrier photodiode (UTC-PD) emitter and Schottky barrier diode detector, which were designed and fabricated for larger bandwidth. Both the emitter and the detector were fabricated on the same epi-layer of the UTC-PD. At the link distance of around 50 cm, a bit error rate of less than 1 × 10 -10 has been achieved with the transmitted power from the UTC-PD of less than 200 μW and effective antenna gains of 40 and 35 dBi in the emitter and detector sides, respectively.

High-Efficiency Ferroelectric-Film Solar Cells with an n-type Cu2O Cathode Buffer Layer

Abstract: Becasue of the existence of interface Schottky barriers and depolarization electric field, ferroelectric films sandwiched between top and bottom electrodes are strongly expected to be used as a new kind of solar cells. However, the photocurrent with a typical order of μA/cm2 is too low to be practical. Here we demonstrate that the insertion of an n-type cuprous oxide (Cu2O) layer between the Pb(Zr,Ti)O3 (PZT) film and the cathode Pt contact in a ITO/PZT/Pt cell leads to the short-circuit photocurrent increasing 120-fold to 4.80 mA/cm2 and power conversion efficiency increasing of 72-fold to 0.57% under AM1.5G (100 mW/cm2) illumination. Ultraviolet photoemission spectroscopy and dark J–V characteristic show an ohmic contact on Pt/Cu2O, an n+–n heterojunction on Cu2O/PZT and a Schottky barrier on PZT/ITO, which provide a favorable energy level alignment for efficient electron-extraction on the cathode. Our work opens up a promising new method that has the potential for fulfilling cost-effective ferroelectri...

Graphene/ZnO nanowire/graphene vertical structure based fast-response ultraviolet photodetector

Abstract: time, and recovery speed of our UV detectors are 8 � 10 2 , 07s, and 05s, respectively, which are significantly improved compared to the conventional ZnO NWs photodetectors The improved performance is attributed to the existence of Schottky barriers between ZnO NW and graphene electrodes The graphene/ZnO NW/graphene vertical sandwiched structures may be promising candidates for integrated optoelectronic sensor devices V C 2012 American Institute of Physics [http://dxdoiorg/101063/14724208] ZnO, as a wide direct band gap (337eV) compound semiconductor with large exciton binding energy (60meV), has been widely investigated for its potential applications in optoelectronic devices, gas and chemical sensors 1,2 Due to large surface-to-volume ratio, ZnO nanowires (NWs) exhibit highly susceptible photoelectric properties by means of electron-hole generation or recombination during ultraviolet (UV) illumination Therefore, ZnO NWs have great potential in high sensitivity and fast-response UV sensors, 3 environmental monitors, and optical communications 4 Recently, Hu et al 5 reported ZnO NW based UV sensors using Schottky contact formed between ZnO and Pt electrode and the device performance such as the sensitive and UV response, is much higher than that of the traditional ZnO NW photoconductivity based UV sensors The UV detectors based on Schottky barriers formed between ZnO NW and other metal electrodes, such as gold electrodes, have also been studied 6,7 Nevertheless, metal electrodes are poor in transparency and can dramatically influence the absorption efficiency of the UV sensors Graphene, a monolayer sp 2 carbon atoms with unique physical properties, such as high mobility and conductivity, 8 high optical transparency 9 and mechanical flexibility, 10 etc, has attracted great research interest recently The high conductive and optical transparent properties make graphene an ideal candidate for the application in transparent electrode The Schottky barrier is also expected to be existed at the interface between ZnO nanowire and graphene, and it has been utilized for light-emitting diodes 11 and transparent nanogenerators 12 In this letter, we have fabricated a vertical sandwich structure of graphene/ZnO NW/graphene We demonstrate the high performance of our ZnO NW based vertical UV photodetector due to the existence of Schottky barriers between graphene electrodes and ZnO NW The current on-off ratio of the UV detector is up to 8 � 10 2 at a illumination power density of 50lw/lm 2 , the photocurrent

Waveguide based compact silicon Schottky photodetector with enhanced responsivity in the telecom spectral band

Abstract: We experimentally demonstrate an on-chip compact and simple to fabricate silicon Schottky photodetector for telecom wavelengths operating on the basis of internal photoemission process. The device is realized using CMOS compatible approach of local-oxidation of silicon, which enables the realization of the photodetector and low-loss bus photonic waveguide at the same fabrication step. The photodetector demonstrates enhanced internal responsivity of 12.5mA/W for operation wavelength of 1.55µm corresponding to an internal quantum efficiency of 1%, about two orders of magnitude higher than our previously demonstrated results [22]. We attribute this improved detection efficiency to the presence of surface roughness at the boundary between the materials forming the Schottky contact. The combination of enhanced quantum efficiency together with a simple fabrication process provides a promising platform for the realization of all silicon photodetectors and their integration with other nanophotonic and nanoplasmonic structures towards the construction of monolithic silicon opto-electronic circuitry on-chip.

Impact of Bi Deficiencies on Ferroelectric Resistive Switching Characteristics Observed at p-Type Schottky-Like Pt/Bi1–δFeO3 Interfaces

Abstract: This work reports a resistive switching effect observed at rectifying Pt/Bi1–δFeO3 interfaces and the impact of Bi deficiencies on its characteristics. Since Bi deficiencies provide hole carriers in BiFeO3, Bi-deficient Bi1–δFeO3 films act as a p-type semiconductor. As the Bi deficiency increased, a leakage current at Pt/Bi1–δFeO3 interfaces tended to increase, and finally, rectifying and hysteretic current–voltage (I–V) characteristics were observed. In I–V characteristics measured at a voltage-sweep frequency of 1 kHz, positive and negative current peaks originating from ferroelectric displacement current were observed under forward and reverse bias prior to set and reset switching processes, respectively, suggesting that polarization reversal is involved in the resistive switching effect. The resistive switching measurements in a pulse-voltage mode revealed that the switching speed and switching ratio can be improved by controlling the Bi deficiency. The resistive switching devices showed endurance of >105 cycles and data retention of >105 s at room temperature. Moreover, unlike conventional resistive switching devices made of metal oxides, no forming process is needed to obtain a stable resistive switching effect in the ferroelectric resistive switching devices. These results demonstrate promising prospects for application of the ferroelectric resistive switching effect at Pt/Bi1–δFeO3 interfaces to nonvolatile memory.

On-chip power-combining for high-power schottky diode based frequency multipliers

Abstract: A novel MMIC on-chip power-combined frequency multiplier device and a method of fabricating the same, comprising two or more multiplying structures integrated on a single chip, wherein each of the integrated multiplying structures are electrically identical and each of the multiplying structures include one input antenna (E-probe) for receiving an input signal in the millimeter-wave, submillimeter-wave or terahertz frequency range inputted on the chip, a stripline based input matching network electrically connecting the input antennas to two or more Schottky diodes in a balanced configuration, two or more Schottky diodes that are used as nonlinear semiconductor devices to generate harmonics out of the input signal and produce the multiplied output signal, stripline based output matching networks for transmitting the output signal from the Schottky diodes to an output antenna, and an output antenna (E-probe) for transmitting the output signal off the chip into the output waveguide transmission line.

Fast-Switching GaN-Based Lateral Power Schottky Barrier Diodes With Low Onset Voltage and Strong Reverse Blocking

Abstract: GaN-based heterostructure lateral Schottky barrier diodes (SBDs) grown on n-SiC substrate are investigated in this letter. These SBDs own very low onset voltage VF = 0.43 V, high reverse blocking VBR >; 1000 V, very low capacitive charge of 0.213 nC/A, and a very fast recovery time of 10 ps. These unique qualities are achieved by combining lateral topology, GaN:C back-barrier epitaxial structure, fully recessed Schottky anode (φB = 0.43 eV), and slanted anode field plate in a robust and innovative process. Diode operation at elevated temperature up to 200 °C was also characterized.

Back-to-back Schottky diodes: the generalization of the diode theory in analysis and extraction of electrical parameters of nanodevices

Abstract: We report on the analysis of nonlinear current?voltage characteristics exhibited by a set of blocking metal/SnO2/metal. Schottky barrier heights in both interfaces were independently extracted and their dependence on the metal work function was analyzed. The disorder-induced interface states effectively pinned the Fermi level at the SnO2 surface, leading to the observed Schottky barriers. The model is useful for any two-terminal device which cannot be described by a conventional diode configuration.

Nanowire Piezo-Phototronic Photodetector: Theory and Experimental Design

Abstract: one-dimensional structures of these materials are ideal for fabricating strain-controlled piezo-phototronic devices. The strain applied to cause the deformation of the nanowires is mainly through shape change of the fl exible substrate that supports the device. Such devices can be the basis for active fl exible electronics, which uses the mechanical actuation from the substrate for inducing new electronic/optoelectronic effects. As the piezopotential is controlled by externally applied mechanical deformation with different orientation and magnitude, the piezo-phototronics effect can be combined with fl exible optoelectronics to promote new device functions. Previously, we have demonstrated the enhancement of the sensitivity of UV photodetector, [ 6 ] the response of photocells, [ 7 ] and the emission effi ciency of light emitting diodes. [ 8 ] In these reports, the coupling between piezoelectric effect and photoexcitation has been investigated experimentally. Theoretical calculation of the piezopotential along ZnO nanowires under different strain has been carried out, [ 9‐11 ] and a theoretical framework has been built for the two-way coupling between the piezoelectric effect and semiconductor transport properties. [ 12 ] Theoretical study for the three-way coupling in piezophototronics remains to be investigated. Constructing such a model will not only provide an in-depth understanding about the experimental results, but also explore the core phenomena and build high performance devices. Besides piezo-phototronic effect, other factors such as piezoresistance effect and change of contact area or contact condition can also affect the device performance. It is important to distinguish the contribution made by the piezo-phototronics effect from these other factors through theoretical analysis. In this paper, we have constructed a theoretical model and fabricated corresponding experimental devices to study the piezo-phototronic photodetectors based on single-Schottky and double-Schottky contacted metal‐semiconductor‐metal (MSM) structures. We have coupled the photoexcitation and piezoelectric terms into basic current equations to study their infl uence on the fi nal device performance. Theoretically predicted results have been quantitatively verifi ed by photodetectors based on CdS nanowires for visible light and ZnO nanowires for UV light. Our experimental results show that the piezo-phototronic effect dominates the performance of the photodetector rather than other experimental factors. It is shown that the piezophototronic effect is signifi cantly pronounced at low light intensities, which is important for extending the sensitivity and application range of the photodetector. The conclusions drawn on Schottky contacts present the core properties of the effect and can easily be extrapolated to other structures like p-n junctions. Finally, based on the theoretical model and experimental results, we have proposed three criteria for describing the contribution made by the piezo-phototronic effect to the performance of the photodetectors, which are useful for distinguishing this effect from other factors in governing the performance of the photodetector. The theoretical model for two-way coupling in piezotronics has been developed in a previous report. [ 12 ] Here we adopt the same assumptions and follow similar methods, as schematically shown in Figure 1 . The depletion approximation is assumed for the Schottky contact. Piezoelectric polarization is induced in a semiconductor nanowire when it is subjects to strain, it is reasonable to assume that the piezo charges are distributed in a layer in the depletion zone, which tune the Schottky barrier height. The formation of an inner potential will drive the free charge carriers to redistribute. If there is no external bias, the inner electric fi eld and net charges should only exist in the depletion zone at static or quasi-static state. The Schottky contact current equation will be used as the basic starting point. The infl uence of photoexcitation and piezo-charges on the material band structure will be discussed, and the fi nal coupled term will be integrated into the current transport equation. To give more intuitive perspective of the piezo-phototronic effect, we have also carried out numerical simulations. A one-dimensional model and other simplifi cations are adopted for easy understanding. The core equations and conclusions are shown in the anayltical model below. Current Density for a Forward Schottky Contact : For a piezophototronic photodetector, a measurement of the photoninduced current is an indication of photon intensity. The coupling effect of piezoelectricity and photon excitation is also

Practical Design and Implementation Procedure of an Interleaved Boost Converter Using SiC Diodes for PV Applications

Abstract: The implementation of an interleaved boost converter (IBC) using SiC diodes for photovoltaic (PV) applications is presented in this paper. The converter consists of two switching cells sharing the PV panel output current. Their switching patterns are synchronized with 180° phase shift. Each switching cell has a SiC Schottky diode and a CoolMOS switching device. The SiC diodes provide zero reverse-recovery current ideally, which reduces the commutation losses of the switches. Such an advantage from the SiC diodes enables higher efficiency and higher power density of the converter system by reducing the requirement of the cooling system. This paper presents also an optimization study of the size and efficiency of the IBC. Based on 1) the steady-state characteristic of the topology; 2) the static and dynamic characteristics of the switching cells; 3) the loss model of the magnetic components; and 4) the cooling system design, the paper provides a set of design criteria, procedures, and experimental results for a 2.5 kW IBC prototype using SiC diodes.

ZnO1–x Nanorod Arrays/ZnO Thin Film Bilayer Structure: From Homojunction Diode and High-Performance Memristor to Complementary 1D1R Application

Abstract: We present a ZnO1–x nanorod array (NR)/ZnO thin film (TF) bilayer structure synthesized at a low temperature, exhibiting a uniquely rectifying characteristic as a homojunction diode and a resistive switching behavior as memory at different biases. The homojunction diode is due to asymmetric Schottky barriers at interfaces of the Pt/ZnO NRs and the ZnO TF/Pt, respectively. The ZnO1–x NRs/ZnO TF bilayer structure also shows an excellent resistive switching behavior, including a reduced operation power and enhanced performances resulting from supplements of confined oxygen vacancies by the ZnO1–x NRs for rupture and recovery of conducting filaments inside the ZnO TF layer. A hydrophobic behavior with a contact angle of ∼125° can be found on the ZnO1–x NRs/ZnO TF bilayer structure, demonstrating a self-cleaning effect. Finally, a successful demonstration of complementary 1D1R configurations can be achieved by simply connecting two identical devices back to back in series, realizing the possibility of a low-te...

Self-powered high performance photodetectors based on CdSe nanobelt/graphene Schottky junctions

Abstract: Self-powered photodetectors based on CdSe nanobelt (NB)/graphene Schottky junctions are fabricated and investigated. Typically such Schottky junctions exhibit good rectifying behavior without light illumination. The on/off ratio is more than 1 × 105 when the voltage changes from −1 to 1 V. Under zero bias, typically such photodetectors show high photosensitivity (∼3.5 × 105), which is defined as (Iphoto − Idark)/Idark, to above-band-gap irradiation. Under 1000 Hz light switching frequency, the response and recovery times of such photodetector are typically 82 and 179 μs, respectively, and the photoconductive gain is 28, greater than unity. The high photosensitivity and gain, as well as fast response speed, guarantee the feasibility of such self-powered photodetectors.

Self-powered and fast-speed photodetectors based on CdS:Ga nanoribbon/Au Schottky diodes

Abstract: Self-powered photodetectors based on CdS:Ga nanoribbons (NR)/Au Schottky barrier diodes (SBDs) were fabricated. The as-fabricated SBDs exhibit an excellent rectification characteristic with a rectification ratio up to 106 within ±1 V in the dark and a distinctive photovoltaic (PV) behavior under light illumination. Photoconductive analysis reveals that the SBDs were highly sensitive to light illumination with very good stability, reproducibility and fast response speeds at zero bias voltage. The corresponding rise/fall times of 95/290 μs represent the best values obtained for CdS based nano-photodetectors. It is expected that such self-powered high performance SBD photodetectors will have great potential applications in optoelectronic devices in the future.

Interface trap characterization and electrical properties of Au-ZnO nanorod Schottky diodes by conductance and capacitance methods

Abstract: Schottky diodes with Au/ZnO nanorod (NR)/n-SiC configurations have been fabricated and their interface traps and electrical properties have been investigated by current-voltage (I-V), capacitance-voltage (C-V), capacitance-frequency (C-f), and conductance-frequency (Gp/ω-ω) measurements. Detailed and systematic analysis of the frequency-dependent capacitance and conductance measurements was performed to extract the information about the interface trap states. The discrepancy between the high barrier height values obtained from the I-V and the C-V measurements was also analyzed. The higher capacitance at low frequencies was attributed to excess capacitance as a result of interface states in equilibrium in the ZnO that can follow the alternating current signal. The energy of the interface states (Ess) with respect to the valence band at the ZnO NR surface was also calculated. The densities of interface states obtained from the conductance and capacitance methods agreed well with each other and this confirm that the observed capacitance and conductance are caused by the same physical processes, i.e., recombination-generation in the interface states.

Multifunctional devices and logic gates with undoped silicon nanowires.

Abstract: We report on the electronic transport properties of multiple-gate devices fabricated from undoped silicon nanowires. Understanding and control of the relevant transport mechanisms was achieved by means of local electrostatic gating and temperature-dependent measurements. The roles of the source/drain contacts and of the silicon channel could be independently evaluated and tuned. Wrap gates surrounding the silicide-silicon contact interfaces were proved to be effective in inducing a full suppression of the contact Schottky barriers, thereby enabling carrier injection down to liquid helium temperature. By independently tuning the effective Schottky barrier heights, a variety of reconfigurable device functionalities could be obtained. In particular, the same nanowire device could be configured to work as a Schottky barrier transistor, a Schottky diode, or a p-n diode with tunable polarities. This versatility was eventually exploited to realize a NAND logic gate with gain well above one.

Design and Characterization of a Room Temperature All-Solid-State Electronic Source Tunable From 2.48 to 2.75 THz

Abstract: We report on the design, fabrication and test of an all-solid-state, frequency agile source that produces over across the 2.48-2.75 THz band at room temperature. This frequency-multiplied source is driven by a W-band synthesizer followed by a power amplifier that delivers 350-450 mW (25.5-26.5 dBm) and a cascade of three balanced frequency triplers. The first stage tripler is based on four power-combined six-anode GaAs Schottky diode devices, and the second stage tripler is based on two four-anode GaAs devices. The output tripler uses a single unbiased device featuring two anodes monolithically integrated onto a thin GaAs membrane. The source delivers a record at 2.58 THz at room temperature. This frequency multiplied source is analyzed with a Fourier transform spectrometer (FTS) and the unwanted harmonics are found to be at least 29 dB below the desired signal. This source, when used as the local oscillator for a hot-electron bolometer mixer, will enable heterodyne instruments for future space missions to map the cosmologically-important 2.675 THz HD molecular line.

Photoelectric Effects in Single Domain BiFeO3 Crystals

Abstract: Energy harvesting from sunlight is essential in order to save fossil fuels, which are found in limited amount in the earth's crust. Photovoltaic devices converting light into electrical energy are presently made of semiconducting materials, but ferroelectrics are also natural candidates because of their internal built-in electric field. Although they are clearly uncompetitive for mainstream applications, the possibility to output high photovoltages is making these materials reconsidered for targeted applications. However, their intrinsic properties regarding electronic transport and the origin of their internal field are poorly known. Here, it is demonstrated that under intense illumination and electric field, oxygen vacancies can be controllably generated in BiFeO3 to dramatically increase the conductance of BiFeO3 single crystals to a controllable value spanning 6 orders of magnitude while at the same time triggering light sensitivity in the form of photoconductivity, diode, and photovoltaic effects. Properties of the bulk and the Schottky interfaces with gold contacts are disentangled and it is shown that bulk effects are time dependent. The photocurrent has a direction that can be set by an applied field without changing the ferroelectric polarization direction. The self-doping procedure is found to be essential in both the generation of electron hole pairs and the establishment of the internal field that separates them.

Temperature-Dependent Characteristics of SiC Devices: Performance Evaluation and Loss Calculation

Abstract: Silicon Carbide (SiC) devices have obvious advantages compared with conventional Si devices, and especially so at high temperatures. This paper aims at developing a method for the characterization of SiC JFET conduction and switching losses at high temperatures as well as the calculation of semiconductor losses in SiC JFET-based converters. To this end, the steady-state performance of SiC JFET and Schottky diodes at different temperatures is studied, and an improved conduction loss evaluation is proposed considering the bidirectional conduction paths of the JFET. Specifically, a SiC JFET bridge test bed is built to measure the switching losses at different temperatures with and without antiparallel diodes, where experimental results show that using SiC Schottky diodes in antiparallel eliminates the reverse recovery of the JFET body diode, improving the switching behavior and reducing the losses of the devices. Further, these test results are used to estimate the losses of a 10-kW ac-dc-ac converter, which shows that the use of Schottky diodes as freewheeling devices helps reduce both conduction and switching losses, presenting an even greater reduction at higher operating temperatures.

Graphene-based Schottky junction solar cells

Abstract: The Schottky junction, with merits of material universality, low cost and easy fabrication, is an alternative structure for solar cells. Compared to traditional indium-tin-oxide (ITO) based Schottky junction solar cells, graphene-based ones have merits of low cost, performance stability, and are applicable to flexible devices. In this highlight, we survey the recent research on graphene-based Schottky junction solar cells, including graphene-on-silicon Schottky junction solar cells and graphene/single NW (NB) Schottky junction solar cells. The working principle of them is discussed. These works demonstrate that graphene-based Schottky junction structures are promising candidates for developing diverse novel high-efficient and low-cost photovoltaic devices. The perspective and challenge of them are also discussed and anticipated.