Forward Bias Research Articles

Self-cooling in reverse biased p-InAsSbP/n-InAs0.9Sb0.1 heterostructures

2D thermal radiation distribution together with I–V and L–I characteristics has been measured and analyzed in forward and reverse biased p–n heterostructures based on InAs0.9Sb0.1 and grown onto n-InAs substrates. The measurements revealed a sufficient difference in the temperature distribution onto the sample surface at forward and reverse bias, which is explained by an impact of heat pump operation initiated by an electron–phonon interaction at the p–n junction and diode contacts at U < 0.

Sub-volt forward-biased silicon microring modulator at 210 Gb/s.

Low-voltage and efficient optical modulators in the silicon photonic (SiPh) platform are highly desired for realizing high-speed connectivity in chip level interconnects, data center interconnects, and high-performance computing (HPC). With the modulator operating at CMOS compatible voltages, high-voltage modulator drivers are no longer needed, thus reducing driver design complexity and power consumption. We demonstrate a silicon microring modulator (MRM) operating at a driving voltage of 0.8 Vpp. We achieve high modulation efficiency by using a small forward bias of 0.2 V: the forward bias voltage allows the modulator to have an enhanced optical modulation amplitude (OMA) by operating near injection mode, modulating 180 Gb/s (180 Gbaud) non-return-to-zero (NRZ) and 210 Gb/s (105 Gbaud) 4-level pulse amplitude modulation (PAM-4) free of electrical or optical amplification. We also demonstrate the operation at zero bias and achieve up to 200 Gb/s. Error-free operation was observed at 130 Gb/s (NRZ). The absence of an external biasing voltage can further improve energy efficiency and simplifies device integration.

Suppressing the Dark Current Under Forward Bias for Dual‐Mode Organic Photodiodes

AbstractTremendous research efforts are developed to suppress the reverse dark current (Jd) and enhance the responsivity of organic photodiodes (OPDs). The functional layers of traditional OPDs usually follow the principle of energy level alignment to make unobstructed photo‐carriers transport under reverse bias, but this inevitably leads to a large forward Jd. Herein, a universal strategy is proposed to manipulate the carrier dynamics and effectively suppress the forward Jd of OPDs, that is, tuning the energy level and electron traps of the anode interface layers (AILs). The bandgap and electron traps of typical organometallic chelate AIL (PEIE‐Co) can be well controlled by adjusting the component ratio of PEIE and metal ions. The wide bandgap increases the carrier injection barrier under reverse and forward bias, endowing OPD with a much lower Jd; the electron traps induce hole tunneling injection by capturing photo‐generated electrons under forward bias, thereby enabling the photomultiplication effect. The obtained OPD exhibits photoconductive/photomultiplication working mode at reverse/forward bias and the specific detectivity approaches ≈1013/1012 Jones, showing promise for adaptively detecting faint and strong light. This study presents an intelligent strategy to achieve dual‐mode OPDs, paving the way for the multifunctional development of photodetectors.

Suppressed gate leakage and enlarged gate over-drive window of E-mode p-GaN gate double channel HEMTs

A 600-V p-GaN gate double channel HEMT (DC-HEMT) is presented with a systematic investigation of the gate characteristics, including the leakage current, breakdown, and reliability under forward bias stress. It is found that the gate leakage of the DC-HEMT is substantially lower than that of the p-GaN single channel HEMT (SC-HEMT) owing to suppressed electron spillover that stems from hole storage in the quantum well upper channel. Consequently, the gate breakdown voltage of the DC-HEMT is improved to 14.7 V compared to 12.2 V of the SC-HEMT. Besides, the gate operating voltage margin of the DC-HEMT is expanded to 4.2 V compared to 3.3 V of the SC-HEMT according to the gate lifetime evaluation.

Bipolar Membranes With Controlled, Microscale 3D Junctions Enhance the Rates of Water Dissociation and Formation

AbstractA soft lithographic method is developed for making bipolar membranes (BPMs) with catalytic junctions formed from arrays of vertically oriented microscale cylinders. The membranes are cast from reusable polydimethylsiloxane (PDMS) molds made from silicon masters, which are fabricated on 2″ to 4″ wafer scales by nanosphere lithography. High‐aspect‐ratio junctions are made on a length scale similar to the thickness of optimized catalyst layers for water dissociation, creating a platform for probing the dual effects of catalysis and local electric field at the microscale BPM junction. Optimized polymer materials and nanoscale metal oxide catalysts are used in this study. 3D BPMs are tested under reverse and forward bias conditions, exhibiting superior performance relative to their 2D counterparts. Under forward bias in H2‐O2 fuel cells, 3D BPMs achieve a current density of 1500 mA cm−2, ≈7 times higher than 2D membranes made from the same materials.

III–V heterostructure tunnel field-effect transistor operation at different temperature regimes

Tunnel field-effect transistors (TFETs) are a potential alternative to MOSFETs for low-temperature electronics. We provide an in-depth experimental characterization of TFETs analyzing the fundamental physical behavior at different temperature regimes. TFET characteristics from 13 to 300 K both in forward and reverse bias are discussed by employing a variation in InAs/InGaAsSb/GaSb heterojunction vertical nanowire devices. Evaluation of the TFET Negative Differential Resistance (NDR) characteristics at different temperatures is established as a technique to probe the dopant incorporation. It is observed that the temperature dependence of the Fermi degeneracy and Fermi-Dirac distribution largely influences the transistor performance at each operating temperature. Our investigation reveals that the TFETs demonstrate lower subthreshold swing than the physical limit of MOSFETs above 125 K. For low-temperature applications, the devices can be operated down to a low operating bias of 0.1 V, while for high temperature, a larger bias of 0.3 V is preferred.

Features of current flow in the n-CoFe2O4/n-CdTe heterojunction

n-CoFe2O4/n-CdTe heterojunctions with a current rectification ratio of 3·105 at voltages |V| = 1.5 V were made by spray pyrolysis of aqueous solutions of cobalt and iron salts on n-CdTe substrates. Based on the analysis of the temperature dependence of I-V-characteristics in the forward voltage range, a change in the mechanisms of current flow in n-CoFe2O4/n-CdTe heterojunctions was established from overbarrier at voltages of 3kT/q < V < 0.3 V to tunneling at voltages of 0.4 V < V < 1 V. The role of surface states in the formation of the energy profile of the heterojunction and the participation of energy levels in the band gap of n-CdTe in the formation of the tunnel current have been clarified. The reasons for the occurrence of negative differential resistance at the forward biases of the structure have been clarified. The current at reverse biases in the range −3 V < V < -3kT/q was analyzed. According to the analysis of the C-V-characteristics, an inversion layer was found in the heterojunction and its behavior from voltage was explained.

Chemical and structural features of spin-coated magnesium oxide (MgO) and its impact on the barrier parameters and current conduction process of Au/undoped-InP Schottky contact as an interfacial layer

This work examines the structural and chemical characteristics of spin-coated magnesium oxide (MgO) on undoped InP (un-InP) and its effects on the barrier parameters and current transport phenomena in the Au/un-InP Schottky contact (SC). Using XRD and XPS, the structural and chemical features of MgO are assessed, confirming that the MgO was deposited on un-InP. The current-voltage (log(I)-V) features were measured for the SC and Au/MgO/un-InP metal/insulator/semiconductor (MIS)-type Schottky contact. The MIS contact revealed an excellent rectification behavior as compared to the SC. The calculated barrier height (Φb) was higher for the MIS contact (0.61 eV) than the SC (0.52 eV), which implies that the MgO interlayer influences the Φb of the SC. The Φb was also estimated using the Cheung’s, Mikhelashvili and Norde procedures, the values are similar, indicating their stability and reliability. The acquired interface state density (NSS) of the MIS contact was less than the SC, proving that the MgO interlayer reduced the NSS. The ohmic behavior was observed in the lower bias region for the SC and MIS contacts, while the trap-free space-charge-limited current (SCLC) was noted in the moderate and upper bias regions of the MIS contact under forward bias. Poole-Frenkel emission (PFE) governs at a lower bias, while Schottky emission (SE) dominates at the upper bias of SC and MIS contacts under reverse bias. These findings demonstrate the potential application of MgO interlayer in advancing electronic devices.

Generating stacking faults in 4H–SiC junction transistor by indentation and forward biasing

Stacking faults in silicon carbide have been widely studied due to their negative impact on the application of silicon carbide in the power electronics industry. In this work, with the assistance of forward biasing, we observe several triangular shaped structures emerging near the indenter imprint in two separate 4H–SiC bipolar junction transistor samples that were deformed by nanoindentation. Based on the study of electroluminescence spectra on one of the samples, the emission peak at 420 nm indicates the formation of single Shockley stacking faults inside deformed transistors. We conclude that the use of indentation can provide a method to study recombination induced stacking faults in silicon carbide junction devices by intentionally introducing dislocations at selected areas of interest.

Electrically reconfigurable MoO3/InSe van der Waals heterojunctions

Abstract Van der Waals (vdW) heterojunctions formed by stacking different layers of two-dimensional atomic crystals with atomically sharp interface and versatile band alignment have been considered as promising candidates for construction of nanoelectronic and nanophotonic devices. Here, we demonstrate the electrically reconfigurable behavior in MoO3/InSe vdW heterojunction with a type-III broken-gap band alignment. The electrical reconfigurability is enabled by the ambipolar transport property of InSe, which is achieved through the use of Pt as contact electrodes. By electrostatically doping the indium selenide (InSe), the reconfigurable MoO3/InSe heterojunctions can be converted between p-n and n+-n junctions. As a current rectifier, the MoO3/InSe heterojunction shows rectification ratios of ~ 107 and ~104 for forward and backward bias conditions, respectively. As a photodetector, the MoO3/InSe heterojunction shows stable photo-switching behavior with a ~105 on/off ratio and an ultralow dark current (≈10 fA).The response time is measured to be 500 μs and 300 μs for rise and fall processes, respectively. These results highlight the role of MoO3 with high electron affinity in construction of vdW heterostructure with type-III band alignment and provide a new platform for high performance optoelectronic devices.

I-V Characteristics of Polycrystalline CAZTSe Heterojunction Solar Cells at Different Ag Content and Annealing Temperatures

Since the polycrystalline (Cu1-xAgx)2ZnSnSe4 (CAZTSe) demonstrated good optical absorption performance in the visible region, the focus of the present study is to grow the polycrystalline (Cu1-xAgx)2ZnSnSe4 thin films deposited by thermal evaporation method on silicon substrates with 800 nm thickness and 0.53 nm/sec deposition rate as a function of Ag content (0.0,0.1,0.2) and annealing temperature at 373 K, 473 K. From I-V measurements of Al/n-CdS/p-CAZTSe/n-Si(111)/Al heterojunction solar cells under dark and illumination conditions, we observed that the forward bias current changes roughly exponentially with bias voltage and the ideality factor and saturation current dependence on both x content and different temperatures (Ta).

A 326 nm pure ultraviolet light sources achieved in a Ga[formula omitted]O[formula omitted] microwire heterojunction through interface optimization and surface-modification

Low-dimensional Ga2O3 single-crystals have caused widespread attentions in the potential of developing ultraviolet light sources due to its ultrabroad bandgap, low-budget, high thermally stable, high breakdown voltage and others. Herein, we exhibit a significant route to construct one-dimensional Ga2O3 microwire heterojunction deep-ultraviolet light-emitting diode (LED). The resulting electroluminescence is positioned at 326 nm with a narrow linewidth of about 22.5 nm, which is the shortest wavelengths once published for the Ga2O3-related light sources. In the well-fabricated LED, an intermediate AlN layer enables appropriately to manipulate band alignment of n-Ga2O3/p-GaN heterojunction, thus achieving efficient confinement of electron–holes spreading and radiative recombination within the Ga2O3 microwire active medium. Benefited from surface-modified Pt nanoparticles, the LED’s electroluminescence efficiency and brightness can be plasmonically boosted. More importantly, the peak energy at 3.8 eV obtained under forward bias, which is smaller than the Ga2O3 bandgap, could be resulted from radiative recombination of weakly-bounded electron–holes inside the Ga2O3 microwires. Therefore, the Ga2O3 monocrystalline wires synthesized using high-temperature carbothermal reduction, are expected as promising-looking candidates to develop environmentally friendly, easy miniaturization, highly-stable deep-ultraviolet light sources and photonic devices.

Dark current in FTO/CZTS interface: a comprehensive comparison of practical Vs theoretical approach using SCAPS-1D

This study investigates the deposition of Cu2ZnSnS4 (CZTS) thin films on fluorine-doped tin oxide (FTO) and soda-lime glass (SLG) substrates using radio frequency (RF) sputtering at varying temperatures. A comprehensive characterization employing multiple analytical techniques was conducted. X-ray diffraction (XRD) analyses confirmed the amorphous nature of CZTS films being deposited up to 200 °C, while higher temperatures promoted increased crystallinity, with the presence of (112) and (220) planes observed at 300 °C and 400 °C. Rietveld refinement using Profex software revealed an increase in crystallite size with deposition temperature for films grown at 300 °C and 400 °C. Optical characterization through UV–vis spectroscopy unveiled a decrease in band gap energy with increasing deposition temperature, while the Urbach energy, associated with defects and imperfections, exhibited an inverse relationship with band gap and temperature. Experimental current–voltage (I-V) measurements using a Keithley source meter showed variations in the ideality factor with deposition temperature. SCAPS-1D simulations were performed to model the FTO/CZTS interface, incorporating experimental parameters. The simulated I-V behavior demonstrated a transition from recombination to diffusion-dominated current above 1.3 V forward bias. Simulations yielded higher ideality factors due to increased contributions from recombination and diffusion currents. Overall, this study provides insights into the growth, structural, optical, and electrical properties of CZTS thin films deposited by RF sputtering, enabling a comprehensive understanding of the FTO/CZTS heterojunction characteristics and their dependence on deposition temperature.

Intense violet electroluminescence of thin SiO2 layers with SnO2 nanocrystals

It has been shown that Sn implantation with subsequent annealing in air leads to an increase in the electroluminescence (EL) intensity of SiO2/Si structure by two orders of magnitude. Intense violet EL with a maximum at 3.21 eV was observed at room temperature by the naked eye at forward bias. The observed emission was attributed to radiative recombination in SnO2 nanocrystals synthesized in SiO2 layers. The external quantum efficiency (EQE) increased with decreasing Sn concentration The maximum external quantum efficiency was found to be 0.7 % for the silica film Sn-implanted at the lowest fluence of 2.5 × 1016cm−2. The non-radiative charge transport (shunt current) through the sample and mechanism of EL excitation are discussed. It has been concluded that the Poole–Frenkel mechanism, or tunneling between traps are the most likely mechanisms of charge transport to light-emitting centers.

Design of Concurrent Dual Band Low Noise Amplifier for WLAN Applications

This paper presents a dual band LNA CMOS designed for a Wireless Local Area Network (WLAN) application using CMOS 0.13-µm Silterra technology. The proposed design incorporates forward body bias technique with cascode and notch filter configuration to achieve both low power consumption and high gain. The simulation results demonstrate a total power consumption of 2.39 mW at a low supply voltage of 0.5 V, with a gain of 16 dB at 2.4 GHz and 12 dB at 5.2 GHz. Additionally, input return loss of -12.3 dB and -14.2 dB with noise figures of 2.93 dBm and 4.23 dBm were obtained at 2.4 GHz and 5.2 GHz, respectively. Overall, this research contributes to the development of dual band LNA designs for WLAN applications.

Optimizing Forward Drop and Reverse Leakage Trade‐Off in AlGaN/GaN Lateral Diode with Schottky‐Metal‐Insulator‐Semiconductor Cascode Anode

Herein, AlGaN/GaN lateral diode with the Schottky‐Metal‐Insulator‐Semiconductor (MIS) cascode anode (CALD) to optimize forward voltage drop (VF) and reverse leakage current (ILEAK) trade‐off is proposed. In the CALD device, a normally‐on Ni/HfO2/AlGaN MIS‐controlled channel as well as a lateral Ni/GaN Schottky contact are cascoded at the anode. The designed normally‐on MIS‐controlled channel has high electron concentration at forward bias and prevents high electric‐field at reverse bias, which ensure both low VF and low ILEAK. Meanwhile, the Ni/GaN Schottky contact with a high Schottky barrier height further suppresses the ILEAK. As a result, the fabricated CALD demonstrates an optimized VF–ILEAK trade‐off relationship, including a low VF of 1.6 V and a low ILEAK of 5.2 × 10−8 A mm−1 (at reverse voltage of 400 V), together with a high breakdown voltage (BV) &gt;700 V. These high performances suggest that the CALD can be a promising candidate for GaN power diode applications requiring a better VF–ILEAK trade‐off.

A hBN/Ga2O3 pn junction diode.

The development of next-generation materials such as hBN and Ga2O3 remains a topic of intense focus owing to their suitability for efficient deep ultraviolet (DUV) emission and power electronic applications. In this study, we combine p-type hBN and n-type Ga2O3, forming a pseudo-vertical pn hBN/Ga2O3 heterojunction device. Rectification ratios > 105 (300K) and [Formula: see text]400 (475K) are observed and are amongst the highest values reported to date for ultra-thin hBN-based pn junctions. The measured current under forward bias is ~2mA, which we attribute to the shallow Mg acceptor level (60 meV), and 0.2 µA at -10V. Critically, device performance remains stable and highly repeatable after a multitude of temperature ramps to 475K. Capacitance-voltage measurements indicate widening the depletion region under increasing reverse bias voltage and a built-in voltage of 2.34V is recorded. The hBN p-type characteristic is confirmed by Hall effect, a hole concentration of [Formula: see text] cm-3 and mobility of 24.8 cm2/Vs is achieved. Mg doped hBN resistance reduces by >108 compared to intrinsic material. Future work shall focus on the optical emission properties of this material system.

Facile assembly of SnO2 thin film-based Al/SnO2/Al device for sensing of 260 nm UVC and 365 nm UVA radiation

An Al/SnO2/Al metal-semiconductor-metal (MSM) device was formed by depositing a ~55nm thin film of SnO2 on Si substrate. Structural, surface morphology and optical properties of the SnO2 film were studied. The current-voltage (I-V) characteristics of the device were recorded under the dark condition followed by 260 nm-UVC and 365 nm-UVA illumination conditions. Under the dark condition, the device shows a resistivity of 8.05 Ωcm at V=1.5V bias voltage. The device produces nearly symmetric rectifying-type I-V characteristics under forward and reverse bias conditions. The electrical properties of the device were explained using back-to-back Schottky diode model. Under the dark condition, the ideality factor of the junction under forward and reverse bias were estimated to be 1.08 and 1.72 respectively. The external quantum efficiency of the device under UVC was found to be ~518.72% and specific detectivity reached as high as 1.03×109 Jones at 2.0V with a response time of ~1s. The device showed a high signal-to-noise ratio between 0.5 and 1.5V bias voltages. The values of the ideality factor being greater than 1 was attributed to the presence of point defects in the SnO2 layer as verified by photoluminescence study. This study reveals that the device could be used as a UVC and UVA sensor at a relatively low bias voltage of ~1.5V.

Deep Traps in AlN Hydride Vapor Phase Epitaxy Film on Low-Temperature AlN/Sapphire

Deep trap states were examined in c-plane, Al-polar AlN epilayers, deposited via metal organic chemical vapor deposition on 270 nm thick AlN buffer layers on sapphire substrates. Contacts were created using e-beam deposited Ni through a shadow mask, with I-V characteristics revealing a trapped limited current (TLC) regime and voltage-dependent hysteresis upon light-emitting diode illumination. Thermally stimulated current and photothermal ionization current spectroscopy measurements demonstrated a prominent trap activation energy of approximately 0.75 eV and additional trap energies of 0.6, 0.4, 0.25, 1.05, and 1.1 eV. The observed differences in photocurrent responses between forward and reverse biases suggest that forward bias induces electron trapping at deeper levels, influencing the TLC behavior. Comparisons with bulk n-type AlN crystals from previous studies show similarities in deep trap spectra, suggesting commonality in trap characteristics across different AlN samples.

Schottky Diode Leakage Current Fluctuations: Electrostatically Induced Flexoelectricity in Silicon.

Nearly four decades have passed since IBM scientists pioneered atomic force microscopy (AFM) by merging the principles of a scanning tunneling microscope with the features of a stylus profilometer. Today, electrical AFM modes are an indispensable asset within the semiconductor and nanotechnology industries, enabling the characterization and manipulation of electrical properties at the nanoscale. However, electrical AFM measurements suffer from reproducibility issues caused, for example, by surface contaminations, Joule heating, and hard-to-minimize tip drift and tilt. Using as experimental system nanoscale Schottky diodes assembled on oxide-free silicon crystals of precisely defined surface chemistry, it is revealed that voltage-dependent adhesion forces lead to significant rotation of the AFM platinum tip. The electrostatics-driven tip rotation causes a strain gradient on the silicon surface, which induces a flexoelectric reverse bias term. This directional flexoelectric internal-bias term adds to the external (instrumental) bias, causing both an increased diode leakage as well as a shift of the diode knee voltage to larger forward biases. These findings will aid the design and characterization of silicon-based devices, especially those that are deliberately operated under large strain or shear, such as in emerging energy harvesting technologies including Schottky-based triboelectric nanogenerators (TENGs).