Schottky Behavior Research Articles

Highly-Rectifying Graphene/GaN Schottky Contact for Self-Powered UV Photodetector

In this study, we demonstrated self-powered fast-response ultraviolet (UV) detection based on a highly-rectifying graphene/GaN Schottky contact. The device was fabricated by mechanically transferring a monolayer graphene onto lightly-doped GaN and showed excellent Schottky behaviors, including a high rectification ratio (> 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> ), a close-to-unity ideality factor and a relatively high Schottky barrier height (1.01 eV). At zero bias, the graphene/GaN Schottky photodiodes exhibited a strong photovoltaic response to UV illumination with a competitively short rise/decay time of 221/546 μs. A trap-associated photoconductive mechanism started to dominate the device's response when its bias went beyond -1 V, which could be identified from the suddenly increased responsivity and response time.

Observation of an electrical breakdown at ZnO Schottky contacts in varistors

We report an electrical breakdown (EBD) at metal/ZnO junctions in varistors with Ag-Pd and Pd electrodes. It was found that these junctions show Schottky behaviour with a mean Schottky barrier height (SBH) of 0.70 ± 0.07 eV for Bi-based varistors with Ag-Pd (80−20 %) electrodes and a mean SBH of 0.47 ± 0.03 eV for Pr-based varistors with Pd electrodes. All investigated electrode-to-grain junctions (EGJ) exhibited an EBD of the Schottky barrier in the reverse current direction, whereas the mean EBD voltage for the Bi-based varistors is 3.5 V and 2.5 V for the Pr-based varistors. Observation of electroluminescent light at the EGJ interface clearly indicates that the EBD is related to electron-hole generation, similar to the EBD at the grain boundaries in the ZnO microstructure. This shows that a similar good but asymmetric varistor effect, as it is observed at grain boundaries, can be observed at EGJ.

Dark and photocurrent response of porous Si/GO-PANI and Si/rGO-PANI heterojunctions for photovoltaics applications

Abstract Porous silicon (pSi) surface enhances light trapping in which improves the silicon solar cell performance. Metal assisted chemical etching (MaCE) technique was used to synthesize pSi. The pSi heterojunction with graphene oxide (GO), reduced graphene oxide (rGO), GO-polyaniline(PANI) and rGO-PANI was fabricated and characterized with Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) to investigate chemical bonding, structural and morphological properties respectively. The FTIR signature at around 1300, 1500, and 1600 cm−1 confirmed the signature of C–C stretching vibrations, C = C stretching of the benzenoid ring, and C = N stretching for the quinoid ring in pSi/rGO-PANI heterojunction. The dark and photocurrent of current–voltage (IV) characteristics showed the Schottky behavior was highest for Si/rGO-PANI. Moreover, pSi/rGO-PANI heterojunction showed the highest photosensitivity and photoresponsivity values of 58.92 and 1.25 mAW−1 respectively.

Tuning of MEH-PPV electro-optical properties by incorporation of benzylidene-malononitrile-based small organic molecules

In this work, we report the composite formation of p-N,N-dimethyl-amino-benzylidene-malononitrile (DABMN) and poly [2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV). The microstructure and the electro-optical performance of the composite film were investigated and reveal interaction between DABMN and MEH-PPV. The photoluminescence spectra of the composite showed quenching, while the current-voltage characteristic exhibits a Schottky diode-type behavior with a low threshold voltage. From conductance measurements, the interface state density of the MEH-PPV and MEH-PPV:DABMN was determined as 2.02 × 1014 eV−1 m−2 and 1.27 × 1014 eV−1 m−2, respectively.

In situ grown single crystal aluminum as a nonalloyed ohmic contact to n-ZnSe by molecular beam epitaxy

Novel ohmic contacts to n-ZnSe are demonstrated using single crystal Al films deposited on epitaxially grown ZnSe (100) by molecular beam epitaxy. Electron backscatter diffraction confirmed the single crystalline structure of the Al films. The (110)-oriented Al layer was rotated 45° relative to the substrate to match the ZnSe (100) lattice constant. The as-grown Al-ZnSe contact exhibited nearly ideal ohmic electrical characteristics over a large doping range of n-ZnSe without any additional treatment. The contact resistances are in a range of 10−3Ωcm2 for even lightly doped ZnSe (∼1017cm−3). Leaky Schottky behavior in lightly doped ZnSe samples suggested that Al-ZnSe formed a low-barrier height, Schottky limit contact. In situ grown Al could act as a simple metal contact to n-ZnSe regardless of carrier concentration with lower resistance compared to other reported contacts in literary studies. The reported novel metallization method could greatly simplify the ZnSe-based device fabrication complexity and lower the cost.

Performance characterization of (Pt,Au,Pd)/ZnO/n-Si/Al Schottky structures for varied temperature and UV illumination conditions

Abstract Herein this paper, morphological, electrical and optical (UV) characteristics are explored for ZnO/n-Si based different contact material Schottky heterojunctions through simulations and fabrication. The electron major ZnO crystalline thin films were deposited using RF-sputtering technique on n-type Si wafers. The structural and morphological properties of sputtered ZnO thin film was studied through tapping mode atomic force microscopy (AFM), and scanning electron microscopy (SEM). The electrical characterization of fabricated Schottky structures involved measuring of current-voltage characteristics for different temperatures ranging from 300 K to 400 K. Capacitance-voltage characteristics for fabricated Schottky heterojunctions were measured to estimate barrier height ( φ B ). The effect of temperature on ideality factor (η) and series resistance was also studied for Pd, Au and Pt Schottky heterojunctions. Increasing the lattice temperature from 300 K to 400 K led to gradual decrease in η and series resistance. Pt–ZnO shows the best Schottky behavior with experimental values of rectification ratio of 3.95 × 10 3 followed by 2.25 × 10 2 and 1.5 × 10 2 for Au and Pd respectively at V anode = ± 5 V . The current characteristics of fabricated Schottky structures were studied using 365 nm wavelength UV illumination source for observing detectivity (D) and responsivity (R). Best responsivity and D values were obtained for Pt/ZnO/Si and found to be 0.32 A / W and 4.12 × 10 9 mHz 1 2 / W followed by Au, and Pd. Pt based Schottky structure shows the fastest response to 365 nm UV light illumination with response time ( t r ) of 25 ms and recovery time ( t d ) of 48 ms The obtained values for figure of merits favor the idea of using Schottky junctions for optoelectronic applications.

Schottky anomaly of deSitter black holes

The interplay of black hole and cosmological horizons introduces distinctive thermodynamic behavior for deSitter black holes, including well-known upper bounds for the mass and entropy. We point to a new such feature, a Schottky peak in the heat capacity of Schwarzschild–deSitter (SdS) black holes. With this behavior in mind, we explore statistical models for the underlying quantum degrees of freedom of SdS holes. While a simple two-state spin model gives Schottky behavior, in order to capture the non-equilibrium nature of the SdS system we consider a system with a large number of non-interacting spins. We examine to what extent constrained states of this system reproduce the thermodynamic properties of the black hole. We also review results of a recent study of particle production in SdS spacetimes in light of the Schottky anomaly and our spin models.

Fabrication of interdigitated electrode (IDE) based ZnO sensors for room temperature ammonia detection

Interdigitated electrode (IDE) sensor has been successfully fabricated, characterised and successfully used for ammonia sensing. Silver (Ag) is used as IDE which is fabricated by using DC magnetron sputtering while ZnO sensing layer with three different dopants (Cd, Mg and Y) have been deposited over the Ag sputtered IDE by RF magnetron sputtering. The deposited sensing layer has been characterised by X-ray diffraction (XRD), Photoluminescence (PL) and Hall effect which reveal that typical ZnO characteristics. The room temperature current-voltage characteristics of the fabricated device show the ohmic behaviour for sensors SD1 (10 mol% Cd doped ZnO) and SD2 (10 mol% Mg doped ZnO) while Schottky behaviour for the sensor SD3 (2 mol% Y doped ZnO). The fabricated IDE sensors were exposed to the various concentration of ammonia, and the enhanced ammonia response has been observed compared to thin film sensors. The sensors SD1 and SD2 show higher ammonia response than SD3. However, fast response and speed recovery time were realised for device SD3 compared to SD1 and SD2. Among the three sensors, SD1 shows the maximum ammonia response. The enhanced ammonia sensing of fabricated sensors explained by band bending mechanism in detail.

Synthesis of an electrically conductive square planar copper(ii) complex and its utilization in the fabrication of a photosensitive Schottky diode device and DFT study

A naphthalene based square planar copper(ii) complex shows significant C–H⋯π interactions to form a supramolecular chain structure. The complex shows efficient charge transport and reveals Schottky barrier diode behavior.

ELECTRICAL CHARACTERIZATION OF METAL JUNCTION FORMED WITH PURE AND POLYANILINE-BLENDED POLY(SCHIFF BASE) POLYMER

In this paper, we demonstrate the formation of Schottky contact formed by Al with a new class of synthesized conjugated pure poly(Schiff base) (PSB) and its blend with varied concentrations of polyaniline (PANI). The Schottky behavior was transformed into Ohmic in the blended polymer. PSB was synthesized from the solution of polycondensation of terephthaloyl chloride (T) and 4-(4-hydroxybenzylideneamino)phenol (SB). The polymer showed good thermal stability with [Formula: see text] of 312∘C as determined by thermal gravimetric analysis–differential scanning calorimetry TGA–DSC and high molecular weight [Formula: see text] (g/mol) with coiled conformation as determined by laser light scattering. PBS was blended with various weight percentage ratios of PANI (0, 3, 6, 9, 12, 15 percent by weight of the pristine polymer). The metal contact (Au) was formed and studied in the temperature range of 293–373[Formula: see text]K, which showed that Schottky behavior in the intrinsic polymer with an ideality factor was close to 2 and then reduced to 1.0–1.2 in the blended polymers. In blended polymers, the conduction across the junction was characterized by Schottky emission at low field and Poole–Frenkel emission at high field. The Schottky barrier height showed a small increase with temperature, which was attributed to reduction in the built up of image charge. The Schottky and Poole–Frenkel emission coefficients were also determined and Schottky emission coefficient agreed with the theoretical value, while Poole–Frenkel emission coefficient was small. In short, the metal–semiconductor junction was affected by the blending, while conduction within the polymer remained independent of PANI concentration.

Single step ohmic contact for heavily doped n-type silicon

This work focusses on the metal-semiconductor contact on n-type c-Si wafers and explore the possibility of using magnesium (Mg) to form electron–selective contacts instead of using the conventional Au-Sb films which requires high temperature annealing between 350 and 500 °C. Aluminium (Al) capping layer was added over the magnesium contacts to prevent oxidation of magnesium. Various electrical measurements were performed over thermally evaporated Mg/Al contacts to investigate the conduction properties on both p-type and n-type silicon, where a Schottky behaviour was observed for the p doped silicon, but an ohmic behaviour (V ∝ I) for the n-type doped c-Si samples. The results were further optimised after investigating various thicknesses of the Mg interlayer, with 10 nm of Mg interlayer found to have the least resistance. The resistivity of the optimised structure (n-Si/Mg-10 nm/Al) was calculated, and measurements according to the Transmission Line Method (TLM) showed a contact resistivity of 462 mΩ cm2 ± 20 mΩ cm2. Further investigations were also conducted on the effect of high temperature annealing of the magnesium contact, which showed an increase in resistance with increase in annealing temperature, with the lowest resistance obtained without annealing. Additional investigations focussed on the morphological analysis of the deposited magnesium and its impact on the electrical characteristics.

Simulation and Performance Evaluation of In Ga P/In Ga As/Ga As Dual Channel HEMT

An InGaP/InGaAs/GaAs dual channel High Electron Mobility transistor (HEMT) with three δ doped layers with different doping densities is modeled and simulated in this paper by using two dimensional ATLAS simulation package from Silvaco software. Different DC performances (Drain characteristic and Transfer characteristics) at various voltage levels are analyzed and results are compared by taking the gate length of 500nm and 800nm at two different temperature levels (250k and 300k) to determine the efficiency of the device for high speed digital device applications. The paper describes the effect of parasitic access resistance on device gate length and effect of mobility by varying temperature. High drain current drivability, large carrier densities and better saturation characteristics are realized because of the inclusion of InGaAs channel instead of GaAs DC structure and schottky behavior of InGaP layer. The studied double channel HEMT with proper dimensions and accurate doping profile makes it a promising device for high performance electronics device applications.

Two-step synthesis of few layer graphene using plasma etching and atmospheric pressure rapid thermal annealing

A two-step process using halogen based plasma etching combined with atmospheric pressure rapid thermal annealing has been used to synthesize few layer graphene films on 6H-SiC (0001) surfaces. In this process, the 6H-SiC substrates were etched under different plasma conditions to produce a carbon rich surface layer. This was followed by rapid thermal annealing in a flow of atmospheric pressure Ar to produce the graphene films. The effects of different etching conditions, heating rates, and average and maximum annealing temperatures were investigated. Changes in surface and near-surface composition after each step were characterized by x-ray photoelectron spectroscopy and overall film quality was assessed using Raman spectroscopy. Film defects associated with this synthesis method included a buffer layer between the SiC substrate and graphene as well as oxygen-based defects on the graphene surface. Electrical characterization of these films was performed using both two and four point methods. In the two point measurements, these films exhibited back-to-back Schottky behavior from which the Schottky barrier height, carrier density and mobility were determined. The four point measurements were used to determine the contact and film resistivity as well as the transfer length.

Uniformity investigation of pHEMTs in 3-D MMICs for pre and post multilayer fabrication

This study deals with the uniformity investigation and comparison on the typical behaviour of pseudomorphic high electron mobility transistors (pHEMTs) before and after the 3-D multilayer fabrication. There are seven multilayer fabricated pHEMTs compared with the seven virgin pHEMTs based on drain-source input current, output current, transconductance, off state leakage behaviour, threshold voltage, knee voltage, on-resistance, Schottky barrier height, ideality factor, reverse saturation current, small signal gain and current gain. Below 10% changes in performance can be seen after multilayer fabrication compare to virgin samples and apart from these exceptions, the discrepancies are well within the tolerance and less than 3% in terms of Schottky behaviour. We show that, the application of the 3D-MMIC technology does not cause any visible destruction of pHEMTs performance using seven different samples before and after the multilayer fabrication.

P-nitro-benzylidenemalononitrile molecule importance in the enhancement of the optical and the electrical properties of thin film based on PVK for optoelectronic applications

For the first time, p-nitro-benzylidenemalononitrile was integrated in Poly(9-vinylcarbazole) (PVK) P-type polymer. The UV–Vis spectra showed an enhancement of the optical response of the composite related to a π–π interaction that occurs between conjugated systems of carbazole groups and NO2BMN molecules. The Photoluminescence curves showed a significant quenching that is related to the charge transfer phenomenon occurring between donor and acceptor compounds. The electrical response revealed that the PVK: NO2BMN composite had a diode behavior. Thus, the electrical parameters improved upon the addition of NO2BMN. The capacitance exhibited Mott–Schottky behaviour, indicating the formation of a Schottky junction (band bending) at the PVK: NO2BMN/Al interface. The interface state density Nss and trap state’s time constant values τ of PVK and PVK: NO2BMN were [1.406 (1014 eV−1 m−2), 0.77 µs] and [1.321 (1014 eV−1 m−2), 0.10 µs], respectively. This result was compared to the literature and showed that the NO2BMN enhances the composite performance. From capacitance, the built-in potential and the minority charges concentrations were calculated for the composite. We found the values of Vbi = 2.6 V and NA = 3.49 (1016 cm−3).

Graphene nanoribbons on hexagonal boron nitride: Deposition and transport characterization

Chemically synthesized “cove”-type graphene nanoribbons (cGNRs) of different widths were brought into dispersion and drop-cast onto exfoliated hexagonal boron nitride (hBN) on a Si/SiO2 chip. Using AFM, we observed that the cGNRs form ordered domains aligned along the crystallographic axes of the hBN. Using electron beam lithography and metallization, we contacted the cGNRs with NiCr/Au or Pd contacts and measured their I-V characteristics. The transport through the ribbons was dominated by the Schottky behavior of the contacts between the metal and the ribbon.

UV Photodetector Based on Mg-Doped GaN Thin Films Prepared by Sol-Gel Spin Coating

In this work, sol-gel spin coated of magnesium (Mg) doped gallium nitride (GaN) thin films grown on AlN sapphire substrate was reported. The structural, lattice vibrational, and electrical properties of the deposited films were investigated and compared. X-ray diffraction results show that the deposited films composed of wurtzite structure with preferred orientation of GaN(002). The Raman active phonon modes correspond to the E2(high) and A1(LO) at 568 cm-1 and 733 cm-1 phonon modes of the hexagonal GaN were observed, while a broad peak attributed to the Mg-related lattice vibrational mode was detected at 669 cm-1. The Raman phonon modes were detected by using Raman spectroscopy. Hall effects results show that the resistivity, carrier concentration, and hall mobility of the Mg-doped GaN film was 0.1397 Ω cm, 1.77 × 1018 cm3, and 6.04 cm2/Vs, respectively. Besides, the characteristics of the ultraviolet (UV) photoresponse of the fabricated detector were investigated. The current-voltage characteristics of the Mg-doped GaN UV photodetector exhibits Schottky behaviour. The current-voltage measurements were carried out at room temperature with a computer-controlled integrated Source Meter (Keithley 2400). Lastly, the ideality factor and Schottky barrier heights were calculated using thermionic emission theory.

Modification of Metallic Multiwalled Carbon Nanotubes Properties by 50 Hz Atmospheric Pressure Dielectric Barrier Discharge Plasma

In this study, multiwalled carbon nanotubes (MWCNTs) were modified using low frequency (50 Hz) nonequilibrium plasma, which was generated separately by oxygen and nitrogen dielectric barrier discharge plasma (DBD) at atmospheric pressure. The MWCNTs were treated with oxygen and nitrogen DBD plasma at atmospheric pressure under three different applied voltages, because the MWCNTs surface was closely related to the plasma treatment voltage. The surface and electrical properties of pristine and treated MWCNTs were studied using Transmission Electron Microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy, while the electrical characteristics were measured using a Hall measurement and two-point probe. FTIR showed formation of oxygen-containing groups like C=O and COOH for the O2 DBD plasma, and addition of N–H vibration bending for the N2 DBD plasma. Raman spectroscopy revealed that the ratio of I D/I G increased with increasing discharge voltage of plasma. The ascended I D/I G may be ascribed to the production of several new defects owing to the introduction of oxygen- and nitrogen functional groups recognized by FTIR. The results of Hall measurement showed that the hall mobility increased with the increase of O2 and N2 DBD voltage. Highest hall mobility was measured for MWCNTs treated with nitrogen at 12 kV, which was 172.9 cm2/Vs. It was also found from the two-point probe IV curve that Ohmic behaviour of pristine MWCNTs tended to change to Schottky behaviour after DBD plasma treatment.

AlGaN Ultraviolet Metal–Semiconductor–Metal Photodetectors with Reduced Graphene Oxide Contacts

AlGaN semiconductors are promising materials in the field of ultraviolet (UV) detection. We fabricated AlGaN/GaN UV metal–semiconductor–metal (MSM) photodiodes with two back-to-back interdigitated finger electrodes comprising reduced graphene oxide (rGO). The rGO showed high transparency below the wavelength of 380 nm, which is necessary for a visible-blind photodetector, and showed outstanding Schottky behavior on AlGaN. As the photocurrent, dark current, photoresponsivity, detectivity, and cut-off wavelength were investigated with the rGO/AlGaN MSM photodiodes with various Al mole fractions, systematic variations in the device characteristics with the Al mole fraction were confirmed, proving the potential utility of the device architecture combining two-dimensional materials, rGO, and nitride semiconductors.

Electrical Behavior of a Nanoporous Nb2O5/Pt Schottky Contact at Elevated Temperatures

This paper discusses the effects of temperature on Schottky behavior of anodized niobium pentoxide (Nb2O5) used to form a nanoporous structure film. The application of a typical Schottky diode is limited at high temperature, and studies of different materials used in the fabrication are still in demand. Nb2O5 as a Schottky diode operation at elevated temperature has yet to be investigated. A nanoporous structure has the potential of producing high conductivity and also has the ability to spread heat since it has higher surface area. The structure was synthesized by anodizing niobium foils in ethylene glycol-based solution with 0.4 wt.% of H2O in different anodization times; 4 min, 8 min, 10 min, 40 min and 60 min. The anodized films were then annealed for 30 min at 440°C. The metal contact used for current–voltage (I–V) testing was platinum (Pt) and it was deposited via thermal evaporator at 30-nm thickness. Various characterization tests were conducted. Field emission scanning electron microscopy (FESEM) images suggested that longer anodization time produced larger pore sizes. The x-ray diffraction (XRD) confirmed the crystallization of Nb2O5 to be in an orthorhombic phase, while atomic force microscopy (AFM) showed surface roughness decreasing with longer anodization time. Higher surface roughness produced lower leakage current. I–V tests were conducted under different temperatures of 25°C, 50°C, 75°C, 100°C and 125°C to study the heat effect on I–V Schottky behavior of anodized nanoporous Nb2O5. By testing the I–V characteristics at elevated temperature, the electrical parameters were observed to have strong dependency on temperature. A device with lower thickness and operating at higher temperature produced higher current contribution. From I–V tests, it was observed that the increment of barrier height and decrement of ideality factor will be affected by increased temperature. For Schottky Pt/Nb2O5, barrier height increased in the range from 0.91 to 1.05, while the ideality factor decreased from 2.24 to 1.42.