High Rectification Ratio Research Articles

High rectification ratio metal-insulator-semiconductor tunnel diode based on single-layer MoS2

Single-layer MoS2, with its ultimate atomic thickness, has shown promise to scale down transistors for modern integrated circuitry. On the way to implementing two-dimensional (2D) electronic devices, controlled wafer-scale synthesis of single-layer MoS2, single-layer MoS2 metal-oxide-semiconductor field-effect transistors, ohmic contact of single-layer MoS2 for low contact resistance, etc, have been extensively studied. However, the most commonly used two-terminal electronic component, a diode, which conducts current primarily in one direction, has rarely been reported based on single-layer MoS2. Here, a two-terminal high rectification ratio metal-insulator-semiconductor (MIS) tunnel diode was reported based on single-layer MoS2. The In/Au (10/70 nm) electrode via thermal evaporation was used to form a good ohmic contact with the single-layer MoS2. The Si3N4/Pd/Au (5/10/70 nm) electrode via electron beam evaporation was used to form an MIS tunneling structure with the MoS2, showing a current rectification ratio of up to 107 at room temperature. The high current rectification ratio is realized by controlling the quantum tunneling carrier density and the tunneling barrier width. The single-layer MoS2 MIS tunnel diode fabricated via the silicon technology compatible evaporation method has potential application as a fundamental electronic building block for future 2D electronics.

Photodetector based on heterostructure of two-dimensional WSe2/In2Se3

Heterojunctions formed by two-dimensional (2D) layered semiconducting materials have been studied extensively in the past few years. These van der Waals (vdW) structures have shown great potential for future electronic and optoelectronic devices. However, the optoelectronic performance of these devices is limited by the indirect band gap of multilayer materials and low light absorption of single layer materials. Here, we fabricate photodetectors based on heterojunctions composed of n-type multilayer α-indium selenide (In2Se3) and p-type tungsten diselenide (WSe2) for the first time. The direct band gap of multilayer α-In2Se3 and type-II band alignment of the WSe2/In2Se3 heterojunction enable high optoelectronic performance of the devices at room temperature in the air. Without light illumination, the dark current is effectively suppressed to 10−13 A under −1 V bias and a high rectification ratio of 7.37 × 103 is observed. Upon laser illumination with a wavelength of 650 nm, the typical heterojunction device exhibits a photocurrent on/off ratio exceeding 1.24 × 105, a maximum photo responsivity of 26 mA W−1 and a short photoresponse time of 2.22 ms. Moreover, the heterojunction photodetectors show obvious light response in the wavelength range from 650 nm to 900 nm. The present 2D vdW heterojunctions composed of direct band gap multilayer materials show great potential for future optoelectronic devices.

Electronic properties and photovoltaic performance of VONc-ZnO hybrid junction solar cells

In this work, we investigated the effect of the additional layer of zinc oxide (ZnO) nanoparticles to the active layer of Vanadyl-2,3-naphthalocyanine (VONc) solar cells. The two diodes were prepared using conventional thermal evaporation technique to produce ITO/VONc and ITO/ZnO/VONc heterojunctions. The change of capacitance-voltage characteristics showed that ITO/ZnO/VONc cell has a built-in potential (0.85 ± 0.01 V) higher than that for ITO/VONc cell (0.74 ± 0.02 V). The dark current-voltage characteristics were recorded for the two diodes in the temperature range of 298–393 K. The rectifier behavior of the two diodes at different temperatures has the same behavior, and ITO/ZnO/VONc cell has a higher rectification ratio. This behavior for two diodes suggests that the dominant forward conduction mechanisms found to be thermionic-emission and space charge limited current mechanisms at low and high applied voltage, respectively. The essential parameters of the diode, such as shunt resistance, series resistance, quality factor, and barrier height, were also calculated. The photovoltaic behavior of two devices has been studied with constant illumination of 80 mW/cm2 at room temperature. The efficiency of the cell is increased ten times by adding ZnO layer.

Low-Temperature-Processed Power Schottky Diode Based on Amorphous Indium-Tin-Zinc-Oxide/Indium-Gallium-Zinc-Oxide Bilayer

A Schottky diode based on amorphous wide bandgap oxide semiconductor is experimentally demonstrated with reasonable performance. The Schottky barrier is formed between the room-temperature sputtered amorphous indium-tin-zinc-oxide/indium-gallium-zincoxide bilayer and platinum, and a highly-resistive, selfaligned junction termination region is implemented at only 280 °C. Due to such low-temperature process, oxide-based Schottky diode is very attractive in terms of low manufacturing cost and back-end-of-line (BEOL) integration compatibility. The proposed Schottky diode has an ideality factor of 1.2 and a high rectification ratio of 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> at ±1.5 V. The extracted specific ON -resistance is 7.8 mΩ·mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and the breakdown voltage is 26.4 V. With approximately the same Baliga's figure-of-merit as that of the single-crystal silicon counterparts, the proposed Schottky diode is therefore promising for power electronic applications.

A p-Si/n-GaN diode fabricated by nanomembrane lift-off and transfer-print technique

In this paper, we successfully demonstrated a high quality p-Si/n-GaN heterojunction diode through van der Waals bonding implemented by nanomembrane lift-off and transfer-print technique. A nanoscale native oxide layer is observed at the interface by transmission electron microscope, which plays a role as passivation-layer. The heterojunction diode has excellent electrical performance with a high rectification ratio of 4.75 × 105 at V and a low reverse dark current density of 4.03 × 10–4 A cm−2 at −3 V. In addition, the heterojunction diode responds to both near ultraviolet (375.6 nm) and red light (650 nm) with responsivity of 429.9 mA W−1 and 66.8 mA W−1 (at −3 V) respectively. This result indicates that a large-lattice-mismatched semiconductor heterojunction can be fabricated based on GaN by using transfer-print technique, thereby expanding the operating band of GaN-based detectors from ultraviolet region to visible region.

An Asymmetric Supercapacitor-Diode (CAPode) for Unidirectional Energy Storage.

A new asymmetric capacitor concept is proposed providing high energy storage capacity for only one charging direction. Size‐selective microporous carbons (w<0.9 nm) with narrow pore size distribution are demonstrated to exclusively electrosorb small anions (BF4 −) but size‐exclude larger cations (TBA+ or TPA+), while the counter electrode, an ordered mesoporous carbon (w>2 nm), gives access to both ions. This architecture exclusively charges in one direction with high rectification ratios (RR=12), representing a novel capacitive analogue of semiconductor‐based diodes (“CAPode”). By precise pore size control of microporous carbons (0.6 nm, 0.8 nm and 1.0 nm) combined with an ordered mesoporous counter electrode (CMK‐3, 4.8 nm) electrolyte cation sieving and unidirectional charging is demonstrated by analyzing the device charge‐discharge response and monitoring individual electrodes of the device via in situ NMR spectroscopy.

An Asymmetric Supercapacitor–Diode (CAPode) for Unidirectional Energy Storage

AbstractA new asymmetric capacitor concept is proposed providing high energy storage capacity for only one charging direction. Size‐selective microporous carbons (w&lt;0.9 nm) with narrow pore size distribution are demonstrated to exclusively electrosorb small anions (BF4−) but size‐exclude larger cations (TBA+ or TPA+), while the counter electrode, an ordered mesoporous carbon (w&gt;2 nm), gives access to both ions. This architecture exclusively charges in one direction with high rectification ratios (RR=12), representing a novel capacitive analogue of semiconductor‐based diodes (“CAPode”). By precise pore size control of microporous carbons (0.6 nm, 0.8 nm and 1.0 nm) combined with an ordered mesoporous counter electrode (CMK‐3, 4.8 nm) electrolyte cation sieving and unidirectional charging is demonstrated by analyzing the device charge‐discharge response and monitoring individual electrodes of the device via in situ NMR spectroscopy.

Taper-shaped carbon based spin filter

Carbon based nanostructures play an important role in the development of new devices in order to sustain Moore's law. In this work, taper, fusiform and hourglass shaped structures sandwiched between two carbon-based electrodes are proposed for the first time to achieve a range of potential applications. The transport properties of these structures were also investigated based on density functional theory (DFT) combined with nonequilibrium Green's function (NEGF) formalism. It was found that the negative differential resistance (NDR) phenomena appeared only in the fusiform shaped device, while I-V curves for the other devices showed that they obeyed Ohm's law. Interestingly, the spin polarization rate of the taper device is almost 100%, which implies that this device could be utilized to filter current according to a particular spin direction. In addition, high rectification ratios and spin diode functionality were also obtained. The microscopic physics responsible for these fascinating properties have also been given explanations through the transmission spectrum, the transmission eigenstates and the density of states.

Insights on Si doping on PNRs for NDR with high PVR and diode behaviour with a high rectification ratio

This work uncovers the physics and application of APNRs by doping Silicon and Sulfur as P-type and N-type dopants. Structurally optimized 8APNRs chains were used throughout the work where the electrical properties were calculated using DFT technique. It was found that heavy doping by either P-type or N-type atoms in 8APNRs device produces NDR behaviour but only p-doped APNRs provides higher Peak to Valley Ratio (PVR). Consequently, if both the impurities were doped in an equal proportion to form a PN junction in 8APNRs, NDR occurrence was suppressed by the added opponent dopants and turned to possess rectifying behaviour. Electrical transport characteristics of 8APNRs based PN Junction diode was analyzed using NEGF formalism where a very high rectification ratio (RR) of the order of 1012 was observed which was much higher than what achieved in N doped AGNRs device (RR ~ 102). This observation benchmarks the utilization of PNRs diodes as an ideal rectifier over GNRs.

Processing Strategies for High-Performance Schottky Contacts on n-Type Oxide Semiconductors: Insights from In2O3

Preparation of rectifying Schottky contacts on n-type oxide semiconductors, such as indium oxide (In2O3), is often challenged by the presence of a distinct surface electron accumulation layer. We investigated the material properties and electrical transport characteristics of platinum contact/indium oxide heterojunctions to define routines for the preparation of high-performance Schottky diodes on n-type oxide semiconductors. Combining the evaluation of different Pt deposition methods, such as electron-beam evaporation and (reactive) sputtering in an (O and) Ar atmosphere, with oxygen plasma interface treatments, we identify key parameters to obtain Schottky-type contacts with high electronic barrier height and high rectification ratio. Different photoelectron spectroscopy approaches are compared to characterize the chemical properties of the contact layers and the interface region toward In2O3, to analyze charge transfer and plasma oxidation processes as well as to evaluate the precision and limits of different methodologies to determine heterointerface energy barriers. An oxygen-plasma-induced passivation of the semiconductor surface, which induces electron depletion and generates an intrinsic interface energy barrier, is found to be not sufficient to generate rectifying platinum contacts. The dissolution of the functional interface oxide layer within the Pt film results in an energy barrier of ∼0.5 eV, which is too low for an In2O3 electron concentration of ∼1018 cm-3. A reactive sputter process in an Ar and O atmosphere is required to fabricate rectifying contacts that are composed of platinum oxide (PtOx). Combining oxygen plasma interface oxidation of the semiconductor surface with reactive sputtering of PtOx layers results in the generation of a high Schottky barrier of ∼0.9 eV and a rectification ratio of up to 106. An additional oxygen plasma treatment after contact deposition further reduced the reverse leakage current, likely by eliminating a surface conduction path between the coplanar Ohmic and Schottky contacts. We conclude that processes that allow us to increase the oxygen content in the interface and contact region are essential for fabrication of device-quality-rectifying contacts on various oxide semiconductors.

Effect of annealing time on the structural and optical properties of n-CuO thin films deposited by sol-gel spin coating technique and its application in n-CuO/p-Si heterojunction diode

This paper reports the growth of n-type CuO (copper II oxide) thin film with improved crystallinity on p-Si substrate using sol-gel spin coating process. The electrical conductivity of the deposited film was determined as n-type using Hot point probe measurement. Further, an in-depth analysis of the annealing time effect on the deposited thin film was done to observe its structural and optical properties. The structural characterization of the deposited film was done with the help of X-ray diffraction and Field Emission Scanning electron microscope. The optical parameters, such as reflectance, refractive index were determined in the spectral range of 300 nm - 800 nm with the help of ellipsometry. The effects of annealing time on band gap, extinction coefficient, dielectric constant for the annealed films were also extracted to observe its application for optoelectronic devices. Further, using the film annealed for 15 mins. n-CuO/p-Si hetero-junction diode was fabricated and characterized. The experimentally obtained electrical parameters of the fabricated n-CuO/p-Si hetero-junction diode were also validated by the results of numerical simulation data obtained by usinga commercially available device simulator. The developed hetero-junction was investigated by considering a conventional thermionic model. It showed high rectification ratio equal to 6805 and a barrier height equal to 0.81 eV.

High-temperature (350 °C) oxidized iridium Schottky contacts on β -Ga2O3

Oxidized iridium (IrOx) Schottky contacts (SCs) with excellent high temperature stability were fabricated on 2¯01 β-Ga2O3 single crystal substrates. These IrOx:β-Ga2O3 SCs were operated at temperatures from 24 to 350 °C with only a very small increase in reverse leakage current, while maintaining extremely high rectification ratios (at ±3 V) of more than 10 orders of magnitude at all temperatures, including 350 °C. This remarkable high temperature performance was due to their very high and thermally stable rectifying barriers that, after an initial heat-related improvement, were characterized by zero-bias effective barrier heights of 2.05 ± 0.02 eV and ideality factors of 1.05–1.10, which were almost unchanged by further repeated operation at 350 °C. The reverse leakage current density at 350 °C was only ∼2.3 × 10−9 A cm−2 (∼3.0 pA) at −3 V and ∼7.5 × 10−8 A cm−2 (∼100 pA) at −100 V. These IrOx:β-Ga2O3 SCs represent a significant improvement in high-temperature β-Ga2O3 SC performance, with considerable potential for the fabrication of high temperature β-Ga2O3 rectifying diodes, deep UV photodetectors, and metal-semiconductor field effect transistors.

Achieving high performance Ga2O3 diodes by adjusting chemical composition of tin oxide Schottky electrode

High performance Ga2O3 Schottky barrier diodes (SBDs) are achieved by adjusting chemical composition of SnOx Schottky electrode. The SnOx is produced by radio frequency sputtering under various oxygen partial pressures (PO). A synergic study on Raman, x-ray photoelectron, and optical transmission spectroscopy of the SnOx films illustrates that: the films with PO = 0 ∼ 3.1% consist mainly SnO and Sn with high conductivity; the films with PO = 4.6 ∼ 5.4% are composed of both p-type SnO and n-type SnO2 with high resistance; the films with PO = 10.0 ∼ 13.1% are mainly dominated by n-type SnO2 with low resistivity. In addition, as PO increased from 0 to 3.1%, the SBDs performances are significantly improved due to that the SnO-dominated films reduce effectively the oxygen-deficiency at the Ga2O3 interfaces and the related interface state density. With PO = 5.4%, the high resistive SnOx results in degraded diode performance because that the SnO2 component with oxygen vacancy defects may aggravate the oxygen-deficiency at the Schottky interface. With the optimized PO of 3.1%, the SBD shows high performance with a large barrier height of 1.12 eV, a near unity ideality factor of 1.22, and a high rectification ratio of >1010.

Induced rectification behavior in armchair SiC nanoribbon by Al and P doping

The rectification behavior of the armchair SiC nanoribbons devices with the substitutional aluminum (Al) and phosphorus (P) impurities are investigated using density functional theory (DFT) and non-equilibrium Green’s function (NEGF) frameworks. The band structures of electrodes, molecular energy spectrum, transmission spectrum and projected device density of states are considered to analyze the results. The devices include two armchair SiC nanoribbons with the 7 and 9 atoms widths (named 7ASiCNR and 9ASiCNR, respectively) and the impurities in the center or edge of the electrodes. From the results, we found that the impurities change the electrical behavior and induce rectification of the devices whether the position of the impurities is in the center or edge of the electrodes. Among these devices, the highest rectification ratio has occurred for the 7ASiCNR device with simultaneous Al and P impurities located in the center of electrodes with the value of 2.29 × 1013. Moreover, in this device, the forward bias threshold voltage is near to zero. From the band structure analysis, it is found that by doping of Al (P) atoms in the ASiCNRs, the bands shift upward (downward) so that the electrode became a p-type (n-type) semiconductor. Therefore, the bands became well-matched and the high density of states in the central region is provided. This cause the electrons can be allowed to transport.For both Al and P atoms impurities, the rectification is obtained but the rectification ratio in the case of simultaneous Al and P impurities is more than Al or P doping due to the better matching of energy bands. For example, in the 7ASiCNR devices, the rectification ratio increases from 1.65 × 104 (P-doped) to 2.29 × 1013 (P- and Al-doped).

Rectifying effect in a MoS2 monolayer crossed with an electro-spun PEDOT-PSS nano-ribbon

A chemical vapor-deposited monolayer MoS2 crystal was crossed with an electro-spun PEDOT-PSS nano-ribbon under ambient conditions. The current–voltage (I–V) curve measured across the hetero-junction was nonlinear and asymmetric, similar to a diode. Under thermal equilibrium, electrons flowed from the MoS2 conduction band into the PEDOT-PSS LUMO level. This occurred via band bending that established a constant Fermi level across the interface. Consequently, a potential barrier was formed that restricted the current. Under normal operation in air, the diode turn-on voltage was 0.1 V and the rectification ratio at ± 1 V was 20. The thermionic emission Schottky junction model was employed for data analysis. The ideality factor was 1.9, and height of the barrier was 0.18 eV. The easy fabrication, low turn-on voltage and high rectification ratio could make this diode useful in cheap, low-power-consumption signal rectifiers.

Synthesis of a high-quality Al-doped CdS/Si nanoheterojunction array and characterization of its electrical and electroluminescence properties

A high-quality nanoheterojunction composed of p-type Si nanoporous pillar array (Si-NPA) and n-type CdS:Al was successfully constructed by growing Al-doped CdS film on a silicon nanoporous pillar array via a simple chemical bath deposition method. The fabricated CdS:Al/Si-NPA nanoheterojunction exhibits a pronounced rectification behavior at a low turn-on voltage of ~ 0.5 V, a relatively high rectification ratio of 217 at ± 1.5 V, and good ideality factors of 0.85 in the low-voltage region and 2.45 in a high-voltage region. The electroluminescence spectra of a nanolight-emitting diode based on the nanoheterojunction are dominated by an intense band-edge emission located at ~ 520 nm under a small forward voltage and free from defect emissions. The intensity increased rapidly with the forward voltage. The emission mechanism and CIE chromaticity coordinates of the electroluminescence spectra were also discussed. The obtained CdS:Al/Si-NPA nanoheterojunction could be used for important applications in nanoscale optoelectronic devices.

High-bias negative differential resistance effect in pure, doped and co-doped carbon nanotubes connected to boron nitride nanotubes

The electronic and transport properties of various devices made of carbon nanotube (CNT), B, Al, N-doped and BN, AlN co-doped carbon nanotubes sandwiched between boron nitride nanotube (BNNT) electrodes were investigated using combined density functional theoretical and the non-equilibrium Green's function (DFT-NEGF) methods. The undoped, doped and co-doped CNTs exhibit low band gap which make them suitable for semiconductor devices. The transport properties such as transmission spectrum, density of states (DOS) and current-voltage characteristic of all the devices were determined. A negative differential resistance (NDR) is observed for undoped, doped and co-doped CNTs at high bias (±1 to ±3 V). It is revealed that the NDR region as well as the peak-to-valley ratio of CNT can be tuned by doping B, N, Al, BN and AlN. The rectification ratio of CNT varies with the type of dopant atoms. The NDR effect in the current-voltage curve along with high rectification ratio proffer the potential applications of doped and co-doped CNTs in nano-rectifiers.

GZO/Si Photodiodes Exhibiting High Photocurrent-to-Dark-Current Ratio

ZnO:Ga (GZO)/Si photodiodes having different thicknesses of GZO layer are fabricated by the sol-gel spin-coating method. The photoelectric properties of the devices are investigated by measuring the current- voltage (I-V) characteristics. The photodiodes exhibit high rectification ratio (RR) and relatively low leakage current. Moreover, the best performance of the photodiodes is achieved by the heterojunction with GZO thickness of 35 nm, which has a transmittance over 87% in the visible range, compared to others. The resulting device shows a current RR of 1275 at ±3 V, a low saturation current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ) of 3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> A, and a photocurrent-to-dark-current ratio of 4639 at -3 V under 100 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Structural, chemical, and electrical parameters of Au/MoS2/n-GaAs metal/2D/3D hybrid heterojunction

In this study, Au/MoS2/n-GaAs heterojunction is fabricated with single MoS2 layer and its structural, chemical and electrical parameters are investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and measurement of current-voltage (I-V) characteristics at room temperature. XRD and XPS analysis results confirm the formation of MoS2 layer on the n-GaAs surface. The electrical properties of the Au/MoS2/n-GaAs heterojunction are compared with those of the Au/n-GaAs Schottky junction. Interestingly, the heterojunction possesses a higher barrier height, lower leakage current and higher rectification ratio, in comparison with the Schottky junction. The shunt resistance (RSh) and series resistance (RS) are also assessed for both the junctions. Moreover, the ideality factor (n), barrier height (Φb) and series resistance (RS) are evaluated using Norde, Cheung’s and surface potential (ΨS-V) plots and the results are well-matched. Furthermore, the current transport mechanism is analyzed based on the forward bias I-V data. Lastly, the Poole-Frenkel emission conduction mechanism is employed to control the reverse bias I-V behavior of both Au/n-GaAs Schottky junction and Au/MoS2/n-GaAs heterojunction. The results demonstrate that the Au/MoS2/n-GaAs heterojunction fabricated using a simple technique is suitable for high-quality electronic and optoelectronic device applications.

Mg doping levels and annealing temperature induced structural, optical and electrical properties of highly c-axis oriented ZnO:Mg thin films and Al/ZnO:Mg/p-Si/Al heterojunction diode

In the present study, we investigated the effect of Mg doping level (0, 1, 3, 5, 7, 10, 20 and 30% Mg) and annealing temperature (TA: 773, 823, 873 and 973 K) on the structural optical and electric properties of highly c-axis oriented Mg-doped ZnO (ZMO) thin films deposited on p-Si by sol-gel spin-coating process. The ZMO thin films were analyzed by x-ray diffraction, field emission scanning electron microscopy (FESEM), x-ray photoelectron spectroscopy (XPS), Fourier-transform infrared, ultraviolet/visible (UV/VIS) spectrophotometer. The highly c-axis oriented ZnO hexagonal structure was observed in all thin films. Crystallite size increased at higher annealing temperature (TA), whereas decreased with increasing certain Mg doping ratios except for the 5 and 7%. The FESEM analyses showed that more homogeneous distribution of nanospherical particles, increased in size at higher TA treatments, whereas their size decreased with increasing Mg doping concentrations except for the 5 and 7%. Energy dispersive spectra and XPS analyses confirmed the insertion of Mg2+ within ZnO lattice. Optical band gap value was increased by Mg doping ratio, whereas decreased at higher TA. The ZMO thin films showed a relatively high transmittance, Extinction coefficient decreased with increasing Mg doping ratio, however, increased at higher TA treatments. Refractive index was also decreased at higher Mg doping levels except for the 20% doping level. Depending on the applied voltage and Mg doping level the rectifying behaviour with high rectification ratio was observed from current-voltage (I-V) characteristics of ZMO/p-Si heterojunction diodes. Overall, our study clearly showed that the 20% Mg-doped ZnO thin films had the optimum optical and I-V characterizations.