Fowler-Nordheim Tunneling Mechanism Research Articles

Van der Waals integrated single-junction light-emitting diodes exceeding 10% quantum efficiency at room temperature.

The construction of miniaturized light-emitting diodes (LEDs) with high external quantum efficiency (EQE) at room temperature remains a challenge for on-chip optoelectronics. Here, we demonstrate microsized LEDs fabricated by a dry-transfer van der Waals (vdW) integration method using typical layered Ruddlesden-Popper perovskites (RPPs). A single-crystalline layered RPP nanoflake is used as the active layer and sandwiched between two few-layer graphene contacts, forming van der Waals LEDs (vdWLEDs). Strong electroluminescence (EL) emission with a low turn-on current density of ~20 pA μm-2 and high EQE exceeding 10% is observed at room temperature, which sets the benchmark for the EQE of vdWLEDs ever recorded. Such efficient EL emission is attributed to the inherent multiple quantum well structure and high photoluminescence quantum yield (~35%) of RPPs and a low charge injection barrier of ~0.10 eV facilitated by the Fowler-Nordheim tunneling mechanism. These findings promise a scalable pathway for accessing high-performance miniaturized light sources for on-chip optical optoelectronics.

Investigation of the forward gate leakage current in pGaN/AlGaN/GaN HEMTs through TCAD simulations

In this study, we examined the gate leakage characteristics of normally off pGaN/AlGaN/GaN HEMTs through a simulation study. The Fowler Nordheim Tunneling (FNT) mechanism mainly contributes to the gate leakage process as indicated by the Technology Computer-Aided Design (TCAD) simulation. However, at low bias, the FNT undercalculates the leakage current since the electric field is low in this region. This extra leakage current component at this low bias region can be attributed to the presence of surface traps. Trap-assisted tunneling current along with the FNT current can explain forward leakage characteristics of the pGaN HEMTs. Our TCAD simulations were matched with the experimental data for five devices from four different research groups to support this claim. Using TCAD simulations, we have been able to analyze several device parameters including the various potential drops inside the gate stack structure. We were able to identify some of the trap levels and compare them to the dominant defects expected to be present in the pGaN cap layer. Furthermore, we studied the effects of different device parameters on the gate leakage process in the pGaN HEMT.

Study of optical float-zone grown gallium oxide Schottky barrier diode

β−Ga2O3 based lateral Schottky barrier diodes are fabricated using Ni/Au as Schottky contact and Ti/Au as Ohmic contact. The Sn-doped β−Ga2O3 sample is grown by the optical float-zone technique. The effect of trenches, which are used for mesa isolation, on breakdown voltage is investigated. The device shows near-ideal characteristics in terms of built-in potential. The parasitic series and shunt resistances are extracted, and their dependency on temperature is established. Modeling of temperature-dependent reverse leakage current is demonstrated using the thermionic emission model, Poole–Frenkel emission model, and Fowler-Nordheim tunneling mechanism. The procedure to extract relevant parameters is explained in terms of bias and temperature dependency. The combined model shows excellent agreement with experimental data over a wide range of bias and temperature. The maximum electric field of 2.3 MV cm−1 is achieved.

Fabrication of a Field-Effect Transistor Based on 2D Novel Ternary Chalcogenide PdPS.

Two-dimensional (2D) palladium phosphide sulfide (PdPS) has garnered significant attention, owing to its exotic physical properties originating from the distinct Cairo pentagonal tiling topology. Nevertheless, the properties of PdPS remain unexplored, especially for electronic devices. In this study, we introduce the thickness-dependent electrical characteristics of PdPS flakes into fabricated field-effect transistors (FETs). The broad thickness variation of the PdPS flakes, ranging from 0.7-306 nm, is prepared by mechanical exfoliation, utilizing large bulk crystals synthesized via chemical vapor transport. We evaluate this variation and confirm a high electron mobility of 14.4 cm2 V-1 s-1 and Ion/Ioff > 107. Furthermore, the 6.8 nm-thick PdPS FET demonstrates a negligible Schottky barrier height at the gold electrode contact, as evidenced by the measurement of the temperature-dependent transfer characteristics. Consequently, we adjusted the Fowler-Nordheim tunneling mechanism to elucidate the charge-transport mechanism, revealing a modulated mobility variation from 14.4 to 41.2 cm2 V-1 s-1 with an increase in the drain voltage from 1 to 5 V. The present findings can broaden the understanding of the unique properties of PdPS, highlighting its potential as a 2D ternary chalcogenide in future electronic device applications.

Fowler-Nordheim tunneling mechanism Graphene/GaN ultraviolet position-sensitive detector with high precision for optoelectronic demodulation applications

As an important component of optical sensors, position-sensitive detector (PSD) plays an important role in non-contact measurement systems and is widely used in many important fields. However, the preparation and application of ultraviolet (UV) PSD are still to be studied. Herein, we propose a high precision UV PSD constructed by graphene (Gr)/GaN heterojunction (active area is 5 ×5 mm2) for the first time, and Fowler-Nordheim tunneling mechanism has been used to improve device performance. Benefiting from the FNT, under a weak light power of 0.06 mW/cm2, the PSD is able to determine the position of the UV light spot through the output photocurrent difference, displays high precision (0.16 μA/mm), excellent weak light detection capability，and good linearity without power supply. Besides, the Gr/GaN show an ultralow threshold voltage (0.132 V) of FNT. When the bias is higher than 0.132 V, photogenerated carriers will tunneling the thin insulation layer by the FNT, resulting in a multiplication of the photocurrent. Therefore, under the same power densities light irradiation (0.06 mW/cm2), the device exhibits an ultrahigh responsivity of 1.88 A/W, a remarkable detectivity of 2.71 × 1013 Jones, and a high LDR of over 99.58 at 0 V bias. More importantly, as an optoelectronic demodulator the device realizes the decoding of optical signals into electrical signals, showing great potential for application in non-contact measurement systems.

Study of digital and analog resistive switching memories based on methylammonium lead iodide (MAPbI3) perovskite by experiments and DFT calculations

In this study, a thin film of methylammonium lead iodide (MAPbI3) was employed as the switching layer in the metal/MAPbI3/FTO devices. Two metals, Ag and Cr, were used as active and inert top electrodes to govern the hysteresis effect of memory devices, respectively. While the Cr/MAPbI3/FTO device displayed an analog resistive switching (RS) behavior and a comparatively low ON/OFF ratio of 10, the Ag/MAPbI3/FTO structure displayed digital bipolar RS and a high ON/OFF ratio of 102. The density functional theory simulations suggest that these various behaviors may be caused by variations in the mutual interaction between the iodine vacancy defect and the metal contact properties. The SET process involved switching both devices from a high-resistance state to a low-resistance one using the space charge-limited current mechanism. In the RESET process, the Ag-electrode device is allocated the Poole–Frenkel emission mechanism, and the Cr-electrode device is followed the Fowler–Nordheim tunneling mechanism. The formation and dissociation of iodine vacancy filaments via the dielectric layer were identified as the RS mechanism in both devices. The findings show that organic–inorganic hybrid perovskite has a strong potential for data storage.

Regulating optoelectronics of carbon dots with redox-active dopamine

The electron transfer (ET) processes in carbon-based quantum dots (CDs) have laid to extensive research endeavors due to their tunable optoelectronic properties with alteration in surface functionalization, doping, surface charge, etc. Here, we proffer shreds of evidence on pH-dependent electron transfer and transport properties of undoped CDs (UCDs) and amine-doped CDs (ACDs) with a redox-active neurotransmitter, dopamine (DA). A pronounced pH-dependent photoluminescence (PL) quenching is depicted for both the CDs with DA, where the quenching efficiency substantially increases in alkaline solvents. Taking advantage of the structural transformation of DA from hydroquinone to quinone, the electron accepting capacity can be improved for alkaline pH, which enhances the ET efficiency. The pH-regulated conductance measurements across the metal-CD-metal junction reveal a hike in the conductivity for acidic and alkaline pH relative to the neutral one. The I-V traces of UCDs and ACDs are contributed by an initial linear current rise and non-linear growth at higher bias explicating both direct and Fowler-Nordheim (F-N) tunneling mechanisms. In addition, the incorporation of DA into these CDs, not only significantly increases conductance in all pH media but also enables them to tunnel the potential barrier directly in acidic media, reducing F-N tunneling. These results could provide new avenues for developing reliable optoelectronic devices and sensing probes for a wide range of applications.

Ultrafine Nickel Sulfide-Based Bipolar Resistive Switching Device as Artificial Synapses for Neuromorphic Application

Biologically inspired systems, particularly those that mimic the nervous system of living beings, are becoming more demanded due to their ability to solve ill-posed problems such as pattern recognition or communication with the external environment. Memristors are essential components to replicate high-density networks of biological synapses that control the effectiveness of communication among neurons and implement learning capability because of their tunable conductance. In this study, an organic–inorganic hybrid system of hexamethylenediamine-stabilized ultrafine nickel sulfide particles was synthesized by employing a complexation-mediated route. Here, we propose a nickel sulfide-based memristor as an artificial synapse for neuromorphic application. The current–voltage behavior of the device exhibited bipolar resistive switching with a stable ON and OFF state with an ON/OFF ratio value of 2.5 × 101. The high-conductance state of the device showed the Ohmic conduction mechanism, and the low-conductance state of the device exhibited the Fowler–Nordheim tunneling mechanism. Using identical and nonidentical pulses, the synaptic plasticity behavior of the device was investigated, which revealed the inverse-symmetric and mirror-symmetric patterns, respectively. The device mimicked the spike-time-dependent plasticity properties for Hebbian learning with a conductance value change from −86 to 91%. We also designed the spiking neural network, consisting of 18 synapses and 11 integrated firing neurons, based on the winner-take-all strategy for unsupervised feature learning.

Fowler-Nordheim tunneling mechanism for performance improvement in graphene 2D/GaN 3D heterojunction ultraviolet photodetector

The Fowler-Nordheim tunneling (FNT) is an important tunneling mechanism and an efficient route to improve the photoresponse of a photodetector. Herein, we report the quantum mechanical FNT mechanism based on graphene 2D/GaN 3D ultra-shallow van der Waals heterojunctions ultraviolet (UV) photodetector via atomic layer deposition Al2O3 tunneling layer, and the conversion between direct tunneling (DT) and FNT has also been systematically studied. At reverse bias (<−0.253 V) with the high build-in field, the high-speed photogenerated carriers overcome the thin insulator layer through the FNT, occurring impact ionization during the process resulting in a multiplication of the photocurrent. Consequently, the photodetector demonstrates pronounced photoresponse performances working under a weak light of 5 μW/cm2 at −2 V, including remarkable responsivity (122.57 A/W), ultrahigh specific detectivity (5.63 × 1014 Jones), and high sensitivity (1.29 × 107%), which indicated that the device has excellent weak light detection ability. This work presents a novel route to fabricate high-performance optoelectronic devices by using the FNT tunneling mechanism.

Nanosheet-Compatible Complementary-Field Effect Transistor Logic Non-Volatile Memory Device

This study proposes a logic non-volatile memory (NVM) device based on the state-of-the-art gate-all-around (GAA) nanosheet process. By adopting a complementary FET structure, we not only reduce the layout footprint area but also demonstrate the compatibility with sub-3nm nanosheet CMOS technology. We simulated the device in TCAD for program and erase operations, considering both Fowler Nordheim tunneling and hot carrier injection mechanisms. The memory window is optimized by adjusting the device structure, such as tunneling and blocking oxide thicknesses, top- and bottom-channel width, and the floating gate length, resulting in a significant enhancement in the memory window. Finally, NAND/NOR type CFET logic NVM are demonstrated to reveal the possible applications of gate-all-around stacked junctionless nanosheet transistor towards embedded flash.

Scrutinization of non‒saturation behaviour of reverse current‒voltage characteristics in Ni/SiO2/p-Si/Al diodes

The present work is an endeavour to investigate non‒saturation behaviour of reverse current in Ni/SiO 2 / p -Si/Al over a wide low temperature range of 70–300 K at step of 10 K using well accepted models i.e., Poole-Frenkel emission, Schottky emission and Fowler‒Nordheim tunneling mechanisms. The results of the study revealed that Schottky emission has the dominance over Poole-Frenkel emission in the temperature range of 200–300 K with the trap state activation energy of 0.17 eV. In the remaining temperature range trap assisted tunnelling and involvement of other mechanisms were suggested. Further, the Fowler‒Nordheim tunneling mechanism was found to be effective above reverse bias of 0.5 V over the entire temperature range of 70–300 K. Thus, variation of barrier height with temperature was examined using Fowler‒Nordheim tunneling model and it was found to increase from 0.17 eV to 0.28 eV as temperature varied from 300 to 70 K. The increase in barrier height with decrease in temperature corroborates the decrease in reverse current with temperature. • Reverse current in Ni/SiO 2 /p-Si/Al MIS diodes was analyzed using various models. • Possible current conduction mechanism is predicted for the diode using various employed mechanisms. • Schottky emission process found to be dominating others mechanisms in the temperature range of 200–300 K at low bias range. • Whereas, Fowler-Nordheim tunneling was found to be effective in the bias range between 0.5 and 2.0 V. • The variation of barrier height with temperature was also examined using FNT.

Work function tunning of lithium-doped vanadium oxide for functioning as hole injection layer in organic light-emitting diodes

The hole-injection layer (HIL) plays an important role in the electroluminescent property of organic light-emitting diodes (OLEDs). In this paper, Li-doped VOx was prepared by solution processing under low-temperature annealing conditions and used as a new kind of HIL in OLEDs. It demonstrated the best phosphorescent OLED performance when the molar ratio of Li:VOx was 3%. The turn-on voltage was 3.7 V, the maximum current efficiency (CE) was 69.5 cd A−1 and the maximum power efficiency (PE) was 48.4 lm∙W−1. In contrast to the OLEDs with pristine VOx as HIL, the CE and PE of the OLEDs with Li:VOx were increased by 14.7% and 40.7% respectively. Based on the Fowler-Nordheim tunneling mechanism, doping Li+ in VOx improved the efficiency of hole injection and balanced carriers by adjusting the work function, thereby improving the efficiency of the device. The experimental results indicated that Li-doped VOx film prepared by solution processing is a very potential material as the HIL of high-performance OLED.

Fabrication of the La0.67Ca0.33MnO3 patterns and investigation on I-V characteristic of La0.67Ca0.33MnO3/Nb:SrTiO3

In this paper, 2,2′-bipyridine (BPY) was used as a chemical modifier to prepare the La0.67Ca0.33MnO3 (LCMO) UV-sensitive sol. The LCMO film was micro-fabricated by the UV-sensitivity of sol, which resulted in LCMO patterns with micron-scale microstructures. The micro-fabrication method was further applied in the preparation of LCMO dot array on the Nb:SrTiO3 (NSTO) substrate to form In/LCMO/NSTO heterostructure. The I-V curve of the In/LCMO/NSTO structure exhibited an obvious I-V hysteresis window which indicated that the resistive switching (RS) effect occurred. It is analyzed that the RS effect results from the barriers change at the In/LCMO and LCMO/NSTO interfaces. Further tests revealed that the In/LCMO/NSTO structure could exhibited two different I-V characteristics when the limiting current was 1 and 10 mA respectively, and the mechanisms with these two different limiting currents are analyzed based on the interface barrier, Space-charge-limited current mechanism and Fowler-Nordheim tunneling mechanism.

Electroluminescent Y3Al5O12 nanofilms fabricated by atomic layer deposition on silicon: using Yb as the luminescent dopant and crystallization impetus.

Silicon-based Yb-doped Y3Al5O12 garnet nanofilms are fabricated by atomic layer deposition, which are polycrystalline after annealing at 1150 °C. The sub-nanometer compositional regulation and the Yb2O3 cladding layers, which also work as the luminescent dopants, are critical for the crystallization. Characteristic Yb3+ luminescence at 1030 nm and 970 nm is identified under electrical injection, exhibiting the external quantum efficiency of 0.65% and the fluorescence lifetime of 80-200 µs. The doped Yb3+ are impact-excited by hot electrons stemming from Fowler-Nordheim tunneling mechanism within the Y3Al5O12 matrix, with the excitation cross section of 0.7×10-15 to 6.4×10-15 cm2. This work certifies the manipulation of multi-oxide nanofilms with designed composition and crystallinity, revealing the possibility of developing Si-based optoelectronic devices from crystalline garnet films.

Temperature dependent polarization-switching behavior in Hf0.5Zr0.5O2 ferroelectric film

Ferroelectricity and polarization-switching behavior were investigated in Hf0.5Zr0.5O2 films from 25°C to 150°C. It is found that a large remnant polarization (Pr) of about 30 μC/cm2 is achieved, and Hf0.5Zr0.5O2 films behave a good stability in a wide range of temperature. By analyzing the physical mechanism of leakage current, it indicates that electron conduction mechanism obeys Schottky emission at low voltages, and Fowler-Nordheim (F-N) tunneling mechanism along with space-charge-limited-conduction (SCLC) at high voltages. The temperature dependent polarization switching and related leakage current behaviors reveal a strong thermal activation of the oxygen vacancies, which can explain the varieties of ferroelectricity and leakage current under different temperatures.

Deposition-temperature dependence of structure, ferroelectric property and conduction mechanism of BCZT epitaxial films

Ba0·85Ca0·15Zr0·1Ti0·9O3 (BCZT) epitaxial films were successfully deposited on (001) Nb-doped SrTiO3 substrate, and the effects of deposition temperatures on the structure, ferroelectric property, and conduction mechanism were studied. The results of XRD and AFM verified the well epitaxial structure with smooth surfaces of the deposited BCZT epitaxial films. BCZT epitaxial films deposited at 650 °C exhibited the best ferroelectric property (2Pr = 22.91 μC/cm2, 2EC = 1702.11 kV/cm) and relatively low leakage current density (7.91 × 103 A/cm2). The conduction mechanism of BCZT films corresponds to the space-charge-limited current (SCLC) mechanism and the Fowler-Nordheim (F–N) tunneling mechanism in the low and high electric field range, respectively.

Investigation on the current conduction mechanism of HfZrOx ferroelectric memory

HfZrOx (HZO)-based materials have received much attention due to their special film characteristics in recent years. Ferroelectric random access memory (FeRAM) based on this HZO material also has promising potential as a next generation memory due to its non-volatile characteristics, excellent endurance, and low power consumption. Previous research has mainly focused on the material properties of HZO-based FeRAM. However, an in-depth investigation of the electrical properties of HZO-based FeRAM is necessary to better understand its transporting mechanism. In this contribution, this study aims to investigate the mechanism of an HZO-based metal–ferroelectric-metal capacitor using comprehensive experimental results, including current–voltage, capacitance–voltage, and polarization–voltage measurements. Experiments at various temperatures are also conducted to help verify the transport mechanism. The low current transport by the Fowler–Nordheim tunneling mechanism does not change with temperature, whereas the high current transport via the Schottky mechanism increases with increasing temperature. We found that the orientation of the dipole plays an important role. Finally, we also propose a band model to explain the electron transport in this HZO-based FeRAM.

Electro-Optic Upconversion in van der Waals Heterostructures via Nonequilibrium Photocarrier Tunneling.

Ultrafast interlayer charge transfer is one of the most distinct features of van der Waals (vdW) heterostructures. Its dynamics competes with carrier thermalization such that the energy of nonthermalized photocarriers may be harnessed by band engineering. In this study, nonthermalized photocarrier energy is harnessed to achieve near-infrared (NIR) to visible light upconversion in a metal-insulator-semiconductor (MIS) vdW heterostructure tunnel diode consisting of few-layer graphene (FLG), hexagonal boron nitride (hBN), and monolayer tungsten disulfide (WS2 ). Photoexcitation of the electrically biased heterostructure with 1.58 eV NIR laser in the linear absorption regime generates emission from the ground exciton state of WS2 , which corresponds to upconversion by ≈370 meV. The upconversion is realized by electrically assisted interlayer transfer of nonthermalized photoexcited holes from FLG to WS2 , followed by formation and radiative recombination of excitons in WS2 . The photocarrier transfer rate can be described by Fowler-Nordheim tunneling mechanism and is electrically tunable by two orders of magnitude by tuning voltage bias applied to the device. This study highlights the prospects for realizing novel electro-optic upconversion devices by exploiting electrically tunable nonthermalized photocarrier relaxation dynamics in vdW heterostructures.

Silicon-based electroluminescent polycrystalline Er-doped Yb3Al5O12 nanofilms fabricated by atomic layer deposition

Abstract By virtue of the sub-nanometer compositional regulation realized via atomic layer deposition, polycrystalline Er-doped Yb3Al5O12 (YbAG:Er) garnet nanofilms are fabricated on silicon after annealing above 1100 °C. The crystalline feature is insensitive to slight deviation from the stoichiometric ratio (Yb:Al = 3:5 for Yb3Al5O12). The nanolaminate devices based on YbAG:Er films present Er-related 1531 nm electroluminescence exhibiting the external quantum efficiency of 2.7–5.2% and the power efficiency of 2.4–4.8 × 10−4, whose fluorescence lifetime is estimated as 1–1.2 ms. The doped Er3+ ions are impact-excited by hot electrons stemming from Fowler-Nordheim tunneling mechanism within the Yb3Al5O12 matrix. This work is believed to lay the basis for manipulating multi-oxide nanofilms with designed composition and crystallinity, and developing optoelectronic devices from Si-based crystalline garnet films.

A detailed study on frequency dependent electrical characteristics of MOS capacitors with dysprosium oxide gate dielectrics

Frequency dependent electrical characteristics of Al/Dy2O3/p-Si/Ag MOS capacitors have been systematically investigated incorporating interfacial chemical structures of the capacitors to specify where interface state signals arise from. The results show that capacitance (C) increases with decreasing in the applied voltage frequency due to the response time dependency of the interface states. Conductance (G) curves have a single peak at the relatively high frequencies as expected. Interestingly, the G curves exhibit two distinct peaks at 400 kHz and lower frequencies. These G peaks are associated with acceptor-like interface (Dit,ac) and donor-like interface (Dit,dn) states. Electrochemical analysis has also depicted that non-stoichiometric DySiOx and SiOx bonds are present at the interface between Dy2O3/Si gate stack. Owing to interactions between mobile charge carriers and possible defect sites present at the DySiOx and SiOx, the Dit,ac and Dit,dn signals have been observed at G curves. In addition, the C hysteresis loop widths decrease with decreasing in the voltage frequencies due to opposite polarity and response time dependencies of the Dit,ac and Dit,dn states. The oxide, interface and border trap densities of capacitors exhibit slight frequency variations and their orders are comparable with device used in the state of the art microelectronics technologies. On the other hand, barrier potential varies from 0.97 eV to 1.136 eV depending on the voltage frequencies. Leakage current density was found to be 1.61 × 10−7 Acm−2 at −1 V and Fowler–Nordheim tunneling mechanism dominates the leakage current conduction. Considering to these results, it can be concluded that the Dy2O3 shows promising dielectric and insulating behavior for the application in future microelectronics technology.