Heterojunction Barrier Research Articles

Design of PNP SiGe HBTs Towards 200 GHz fmax

In the three decades of production, SiGe HBTs have numerous applications including RF and high-speed mixed-signal and analog. While successive generations of BiCMOS technologies in the past have employed process and layout scaling, the advanced high performance platforms (with several 100 GHz fmax) have mostly been restricted to SiGe NPN optimization, and the Si PNP is often only offered as a dependent device with significantly slower speed. There truly exists a gap in literature with the PNP device variants showcasing good fT and fmax above 150 GHz in a BiCMOS platform. It is worth noting that much of the serviceable applications above can be designed with NPN-only topologies. However, having the complementary PNP enables several advantages, including power savings, improved gain, reduced design complexity, and improved reliability.There are several challenges for making high performance PNP devices including reduced minority mobility in the intrinsic base from the conducting holes, elevated base current from minority electron injection into the emitter, and heterojunction barrier effect directly on the carrier pathway in the collector-base junction. The figure below shows the measured fT/fmax characteristics for a SiGe PNP with Ae = 0.12x2.5 um2 built using a 130nm technology framework optimized for a PNP-only process. The present work expands on the measured results (AC + DC) and the challenges faced in optimizing PNP performance for 200 GHz fmax and beyond. Figure 1

Band Alignment Semimetal Heterojunction-Based Ultrabroadband Photodetector for Noncontact Gesture Interaction with Low Latency.

Non-contact gesture recognition and interaction (NGRI) revolutionizes the natural user interface, fundamentally transforming human interactions with daily-use technology. Conventional NGRI systems frequently encounter obstacles such as pronounced latency and environmental disturbances, including humidity or lighting conditions, resulting in compromised system fluidity and robustness. This study highlights the utilization of silicon-based semimetal heterojunction photodetectors for precise gesture recognition and seamless human-machine interaction. Through the application of band alignment theory and sophisticated TCAD simulation, heterojunction barriers are successfully optimized by fine-tuning parameters including Si doping concentration and semimetal thickness. By strategically aligning vertical material growth and implementing vertical heterojunction configuration, a room temperature detector with exceptional sensitivity (specific detectivity (D*): ≈1011 Jones), ultra-broad spectral range (405-10600 nm), and rapid response time (≈ µs) is achieved. Harnessing its distinguished speed and sensitivity in detecting human infrared radiation, in conjunction with an advanced spatial-temporal comparison algorithm and a multi-channel high-frequency sampling processing design, a NGRI system with low latency, high precision, minimal energy consumption, and versatility across diverse scenarios has been developed. The results pave the way for non-contact sensor design and may further enhance the practicality and user experience of non-contact human-machine interaction systems.

Vertical Barrier Heterostructures for Reliable and High-Performance Self-Powered Infrared Detection.

With their fascinating properties, emerging two-dimensional (2D) materials offer innovative ways to prepare high-performance infrared (IR) detectors. However, the current performance of 2D IR photodetectors is still below the requirements for practical application owing to the severe interfacial recombination, sharply raised contact resistance, and deteriorated metal conductivity at nanoscale. Here, we introduce a vertical barrier heterojunction with a structure of PtSe2/GaAs that combines the excellent optoelectronic properties of transition metal sulfides with topological semi-metals, which allows for an adjustable bandgap and high carrier mobility. The heterojunction was fabricated using the wet transfer method. The heterostructures show significant rectification behaviors and photovoltaic effects, which allow it to operate as a self-driven photodetector at zero bias. The photoresponse parameters at 850 nm with zero bias voltage are 67.2 mA W-1, 6.7 × 1012 Jones, 9.8%, 3.8 × 105, 164 μs, and 198 μs for the responsivity, specific detectivity, external quantum efficiency, Ilight/Idark ratio, rise time, and fall time, respectively. Moreover, the heterojunction is highly sensitive to a wide spectral band from ultraviolet to near-infrared (360-1550 nm). At the same time, this heterostructure demonstrates significant potential for applications in IR polarized light detection and room-temperature high-resolution IR imaging. The excellent properties of the heterojunction make it well-suited for high-performance, self-powered IR detection.

Rationally designed CaTiO3/Mn0.5Cd0.5S/Ni3C S-scheme/Schottky integrated heterojunction for efficient photocatalytic H2 evolution

Developing effective photocatalysts to achieve stable and efficient solar-induced hydrogen production remains a significant challenge due to rapid photocarrier recombination and sluggish hydrogen evolution kinetics. Here, a multi-interfacial engineering strategy involving the decoration of metallic Ni3C onto CaTiO3/Mn0.5Cd0.5S was proposed to create an S-scheme/Schottky hybrid heterostructure with multiple carrier transport paths for effective photocatalytic H2 production. Exploiting the synergy between S-scheme heterojunction and Schottky barrier, the engineered ternary CaTiO3/Mn0.5Cd0.5S/Ni3C hybrid heterojunction exhibits outstanding photostability and significantly enhanced hydrogen evolution activity of 79.1 mmol g-1 h−1, which was about 4.55, 3.22 and 2.59 times greater than Mn0.5Cd0.5S, Mn0.5Cd0.5S/Ni3C, and CaTiO3/Mn0.5Cd0.5S, respectively. By creating an S-scheme heterojunction between CaTiO3 and Mn0.5Cd0.5S, accompanied by a robust internal electric field (IEF), spatial charge separation can be effectively accelerated while ensuring the simultaneous preservation of highly active electrons and holes. Meanwhile, Ni3C nanoparticles, acting as a Schottky-junction H2 generation cocatalyst, can efficiently trap the photoinduced electrons to establish multiple charge transfer channels and supply ample active sites for photoreduction reaction, thereby further optimizing the hydrogen generation kinetics. The integration of a Schottky barrier and S-scheme heterojunction in this research is expected to offer new perspectives for designing other highly effective hybrid catalysts for solar-to-hydrogen fuel conversion.

P-N Heterojunction formation: Metal Sulfide@Metal Oxide Chemiresistor for ppb H2S Detection from Exhaled Breath and Food Spoilage at Flexible Room Temperature.

The development of a portable, low-cost sensor capable of accurately detecting H2S gas in exhaled human breath at room temperature is highly anticipated in the fields of human health assessment and food spoilage evaluation. However, achieving outstanding gas sensing performance and applicability for flexible room-temperature operation with parts per billion H2S gas sensors still poses technical challenges. To address this issue, this study involves the in situ growth of MoS2 nanosheets on the surface of In2O3 fibers to construct a p-n heterojunction. The In2O3@MoS2-2 sensor exhibits a high response of 460.61 to 50 ppm of H2S gas at room temperature, which is 19.5 times higher than that of the pure In2O3 sensor and 322.1 times higher than that of pure MoS2. The In2O3@MoS2-2 also demonstrates a minimum detection limit of 3 ppb and maintains a stable response to H2S gas even after being bent 50 times at a 60° angle. These exceptional gas sensing properties are attributed to the increase in oxygen vacancies and chemisorbed oxygen on In2O3@MoS2-2 nanofibers as well as the formation of the p-n heterojunction, which modulates the heterojunction barrier. Furthermore, in this study, we successfully applied the In2O3@MoS2-2 sensor for oral disease and detection of food spoilage conditions, thereby providing new design insights for the development of portable exhaled gas sensors and gas sensors for evaluating food spoilage conditions at room temperature.

High breakdown voltage of 1.3 kV and low turn-on voltage of 0.48 V β-Ga2O3 heterojunction barrier Schottky diode with tungsten Schottky contact

β-Ga2O3 power diodes were expected to possess low turn-on voltage (V on), low reverse leakage (J R), and high blocking capability for low power losses. In this work, a low V on (0.48 V) β-Ga2O3 heterojunction barrier Schottky diode (HJBS) with tungsten Schottky contact was achieved. Benefitting from the lateral depletion of p+-NiO to suppress J R originating from the low Schottky barrier, the blocking capability of β-Ga2O3 HJBS was enhanced. The spacing width of p+-NiO was systematically studied to reveal its modulation effect on forward and reverse characteristics. This work provides a promising strategy for improving rectifier efficiency of β-Ga2O3 diodes.

Investigating for Photocatalytic Activity of Hybrid TiO2/Reduced Graphene Oxide and Application in Reducing VOCs

In this study, rGO/TiO2 hybrid nanostructures (rGO : reduced Graphene Oxide) have been successfully fabricated for the purpose of application in the treatment of volatile organic compound (VOCs) that harmful for the environment through the method of directly measuring the change in concentration of decomposed VOCs in real time under UV-excited conditions using a home-made measuring system. the results showed that hybrids TiO2 : rGONFs (reduced Graphene Oxide nano flake) samples with the weight ratio between two kind of material are 99%:1% and 98%:2% which reduced VOCs faster than 2 time intrinsic TiO2. The phenomenon of 2D materials involved in the hybrids lead to the fact that the photocatalytic activity of TiO2 had been significantly improved, this can be explained as follows: When heterogeneous hybrid was formed, because of the difference in energy levels of conduction band between two materials was negligible, heterojunction barrier is not too high this made the photogenerated electrons from TiO2 easily move through rGONFs under UV stimulation. This thing has significantly reduced the recombination of the generated carrier in TiO2 during irradiation, which lead to an increase in the lifetime of the carrier and make photocatalytic reaction of the assembly become more effective. Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Highly Sensitive Narrowband AlGaN Solar Blind Ultraviolet Photodetectors Using Polarization Induced Heterojunction Barrier

Highly Sensitive Narrowband AlGaN Solar Blind Ultraviolet Photodetectors Using Polarization Induced Heterojunction Barrier

A Physics-Based Compact Model for the Static Drain Current in Heterojunction Barrier CNTFETs—Part II: Scattering, High-Field Effects, and Model Verification

A Physics-Based Compact Model for the Static Drain Current in Heterojunction Barrier CNTFETs—Part II: Scattering, High-Field Effects, and Model Verification

A Physics-Based Compact Model for the Static Drain Current in Heterojunction Barrier CNTFETs—Part I: Barrier-Related Current

A Physics-Based Compact Model for the Static Drain Current in Heterojunction Barrier CNTFETs—Part I: Barrier-Related Current

The effects and mechanisms of 2 MeV proton irradiation on high bias conditions of InP/InGaAs DHBTs

In this work, a 2 MeV proton irradiation experiment has been carried out on self-fabricated InP/InGaAs heterojunction bipolar transistors (HBTs) with fluence of 5 × 1013 H+/cm2 and 1 × 1014 H+/cm2. The degradation and mechanisms have systematically been studied under different bias conditions. The irradiated InP-based HBTs have suffered more sever degradation at low and high bias voltages with larger damage coefficient of current gain (Kβ), due to the increased base recombination current and the slacken collector current respectively. Under high injection current densities, the slow-down of collector current and the collapse of current gain (β) have occurred at increasingly smaller biases as irradiation fluence increases. Consistently, the ideality factor of base current collapses to 1 at high injection current, moreover, the collapse point decreases as fluence increases. The aggravated degradation at high current densities is attributed to the influence of heterojunction barrier effect (HBE) by the structure of the multi-layer collector region. The study would be of great significance for optimizing the device structure and improving the irradiation tolerance.

S-scheme regulated Ni2P-NiS/twinned Mn0.5Cd0.5S hetero-homojunctions for efficient photocatalytic H2 evolution

Effective bulk phase and surface charge separation is critical for charge utilization during the photocatalytic energy conversion process. In this work, the ternary Ni2P-NiS/twinned Mn0.5Cd0.5S (T-MCS) nanohybrids were successfully constructed via combining Ni2P-NiS with T-MCS solid solution for visible light photocatalytic H2 evolution. T-MCS is composed of zinc blende Mn0.5Cd0.5S (ZB-MCS) and wurtzite Mn0.5Cd0.5S (WZ-MCS) and those two alternatively arranged crystal phases endow T-MCS with excellent bulk phase charge separation performance for the slight energy level difference between ZB-MCS and WZ-MCS. S-scheme carriers transfer route between NiS and T-MCS can accelerate the interfacial charge separation and retain the active electrons and holes, meanwhile, co-catalyst Ni2P as electron receiver and proton reduction center can further optimize the H2 evolution reaction kinetics based on the surface Schottky barrier effect. The above-formed homo-heterojunctions can establish multiple charge transfer channels in the bulk phase of T-MCS and interface of T-MCS and Ni2P-NiS. Under the synergistic effect of twinned homojunction, S-scheme heterojunction, and Schottky barrier, the ternary Ni2P-NiS/T-MCS composite manifested an H2 production rate of 122.5 mmol h–1 g–1, which was 1.33, 1.24, and 2.58 times higher than those of the NiS/T-MCS (92.4 mmol h–1 g–1), Ni2P/T-MCS (98.4 mmol h–1 g–1), and T-MCS (47.5 mmol h–1 g–1), respectively. This work demonstrates a promising strategy to develop efficient sulfides photocatalyst toward targeted solar-driven H2 evolution through homo-heterojunction engineering.

Radiation Damage and Mitigation by Minority Carrier Injection in InAsSb/AlAsSb Heterojunction Barrier Mid-Wave Infrared Detector

Radiation Damage and Mitigation by Minority Carrier Injection in InAsSb/AlAsSb Heterojunction Barrier Mid-Wave Infrared Detector

A self-aligned Ga2O3 heterojunction barrier Schottky power diode

We report an alignment-free gallium oxide (Ga2O3) heterojunction barrier Schottky (HJBS) power diode, which utilizes the self-assembled Ni nanostructures as in situ masks for the trench etching of Ga2O3 and the subsequent selective-area filling of p-type NiO. By increasing the trench depth to 200 nm, the relevant HJBS diode exhibits improved reverse blocking capabilities including the reduced leakage current density of 10−8 A/cm2 (at a reverse bias of 100 V) and the enhanced breakdown voltage of 748 V, while maintaining the forward biasing characteristics similar to the Schottky barrier diode (SBD). The variation of turn-on voltage and the reverse breakdown features indicate the conversion of the HJBS diodes characteristics from Ni/Ga2O3 SBD to the NiO/Ga2O3 p-n heterojunction diode. The electrical field simulations and experimental facts imply that the remarkable lateral pinch-off effect in the 200-nm trenched diodes shields the electric field in the depletion region underneath the Ni/Ga2O3 Schottky contact. This work provides a straightforward strategy to simplify the fabrication process of Ga2O3-based HJBS diodes with both promising forward and reverse performances.

High sensitivity and selectivity of ZnO nanoparticle-decorated 1D a-MoO3 nanobelts toward ethanol by microwave heating

One-dimensional layer structure a-MoO3 nanobelts with abundant oxygen defects were effectively synthesized through a hydrothermal route and decorated by ZnO nanoparticles via a liquid-phase chemical process. ZnO nanoparticles (NPs) with a size of approximately 50 nm were uniformly dispersed on the a-MoO3 nanobelt surface, forming an n-n heterostructure at the two-phase interface. The crystalline structure, microtopography, element composition, valence state, surface-to-volume ratios, optical properties, and work function of the ZnONP-decorated a-MoO3 samples were analyzed. ZnONP-decorated a-MoO3 nanobelts with different proportions of ZnO were synthesized and subjected to ethanol sensing. The 25% loaded ZnONP-decorated a-MoO3 nanobelts were found to offer the best response (Ra/Rg = 19.2 at 100 ppm), which was 3.6 times higher than that of pristine α-MoO3 (5.37) with a low detection limit (108 ppb). The response time was significantly lower (14–27 s) than that of pristine a-MoO3 (5–8 s). Furthermore, the sensor has ultrahigh selectivity and reliable stability for ethanol. Layered MoO3 nanobelts have a unique sensing mechanism, which is the catalytic oxidation of lattice oxygen on the MoO3 surface to form oxygen vacancies and free electrons. The excellent sensing performance was ascribed to the unique 1-D nanobelt morphology of the a-MoO3 carrier, the abundance of oxygen defects, and the formation of heterojunction barriers at the two-phase interface.

Zinc oxide incorporated molybdenum diselenide nanosheets for chemiresistive detection of ethanol gas

Herein, a room-temperature chemiresistive ethanol gas sensor based on hydrothermally synthesized zinc oxide (ZnO) incorporated-molybdenum diselenide (MoSe2) nanosheets was demonstrated. The sensing properties of the MoSe2/ZnO nanocomposite sensor were investigated systematically by exposing the sensor to various ethanol gas concentrations (10–500 ppm) in dry N2 and dry air. The synergistic effect due to the incorporation of ZnO nanorods in MoSe2 nanosheets was found to enhance the sensor response to ethanol gas (when operated in dry N2) with improved response and recovery time of 8.4 and 14.7 s respectively, high selectivity, stability, and reproducibility. The nanocomposite-based sensor showed high gas sensing response (Rg/Ra) of 37.8 to 500 ppm of ethanol gas. While the response of the nanocomposite-based sensor decreased to 15.3, to 500 ppm of ethanol gas in dry air which suggests that the sensor performs better when operated in dry N2 than in dry air. On the basis of experimental results, a plausible mechanism has been proposed based on the formation of p-n heterojunction and potential barrier modulation at the interface of the MoSe2/ZnO nanocomposite sensor. The results demonstrated that MoSe2/ZnO-based nanocomposite may pave the way for the fabrication of ethanol gas sensors for real-time electronics applications.

Photoelectrochemical Water Splitting with ITO/WO3/BiVO4/CoPi Multishell Nanotubes Enabled by a Vacuum and Plasma Soft-Template Synthesis.

A common approach for the photoelectrochemical (PEC) splitting of water relies on the application of WO3 porous electrodes sensitized with BiVO4 acting as a visible photoanode semiconductor. In this work, we propose a new architecture of photoelectrodes consisting of supported multishell nanotubes (NTs) fabricated by a soft-template approach. These NTs are formed by a concentric layered structure of indium tin oxide (ITO), WO3, and BiVO4, together with a final thin layer of cobalt phosphate (CoPi) co-catalyst. The photoelectrode manufacturing procedure is easily implementable at a large scale and successively combines the thermal evaporation of single crystalline organic nanowires (ONWs), the magnetron sputtering deposition of ITO and WO3, and the solution dripping and electrochemical deposition of, respectively, BiVO4 and CoPi, plus the annealing in air under mild conditions. The obtained NT electrodes depict a large electrochemically active surface and outperform the efficiency of equivalent planar-layered electrodes by more than one order of magnitude. A thorough electrochemical analysis of the electrodes illuminated with blue and solar lights demonstrates that the characteristics of the WO3/BiVO4 Schottky barrier heterojunction control the NT electrode efficiency, which depended on the BiVO4 outer layer thickness and the incorporation of the CoPi electrocatalyst. These results support the high potential of the proposed soft-template methodology for the large-area fabrication of highly efficient multishell ITO/WO3/BiVO4/CoPi NT electrodes for the PEC splitting of water.

Hierarchical NiO/TiO2 heterojuntion-based conductometric hydrogen sensor with anti-CO-interference

Constructing a heterojunction is an effective way to improve the gas sensing properties of metal oxide semiconductors. In this work, a hydrogen sensor containing hierarchical and porous NiO/TiO2 heterojunction bilayer structure was designed. The top layer is formed by the NiO nanowalls grown along the [220] direction with exposed (111) facets, and the bottom layer is formed by the [002] oriented TiO2 nanorod arrays. The exposed high energy crystal surfaces of NiO and TiO2, together with the adapted surface depletion region, induced by the formation of the heterojunction, enable the hydrogen sensor to have both a wide detection range and a much higher response to hydrogen than single layer materials. With the optimized size of the pores existing between the walls, the hydrogen sensor shows excellent prevention to interference from CO. Both the gas diffusion regulated by the porous structure and the surface interaction between H2/CO and O2- controlled by the heterojunction barrier contribute to the distinctive detection of H2 and CO at room temperature (25 ℃ ± 2 ℃).

A compact physical expression for the static drain current in heterojunction barrier CNTFETs

A physics based compact expression for the static drain current in carbon nanotube field-effect transistors (CNTFETs) is presented, which takes into account the impact of heterojunction barriers at the source and drain end of the channel. The new formulation is based on a closed-form solution of the Landauer equation using a Gaussian-like surrogate function for its energy dependent integrand. The model also includes a smooth transition from thermionic emission based transport in the subthreshold region to tunneling dominated transport in the above-threshold regime. The formulation has been verified for both ballistic and scattering dominated carrier transport in the channel based on data obtained from device simulation of a unit cell structure and measurements of fabricated multi-tube high-frequency (HF) CNTFETs. Including the heterojunction barriers enables to capture the different curve shapes of the device characteristics and their differences in linearity compared to devices with ohmic contacts.

Non‐Hermitian Hartman Effect

AbstractThe Hartman effect refers to the rather paradoxical result that the time spent by a quantum mechanical particle or a photon to tunnel through an opaque potential barrier becomes independent of barrier width for long barriers. Such an effect, which has been observed in different physical settings, raised a lively debate and some controversies, owing to the correct definition and interpretation of tunneling times and the apparent superluminal transmission. A rather open question is whether (and under which conditions) the Hartman effect persists for inelastic scattering, that is, when the potential becomes non‐Hermitian and the scattering matrix is not unitary. Here, tunneling through a heterojunction barrier in the tight‐binding picture is considered, where the barrier consists of a generally non‐Hermitian finite‐sized lattice attached to two semi‐infinite nearest‐neighbor Hermitian lattice leads. A simple and general condition is derived for the persistence of the Hartman effect in non‐Hermitian barriers, showing that it can be found rather generally when non‐Hermiticity arises from nonreciprocal couplings, that is, when the barrier displays the non‐Hermitian skin effect, without any special symmetry in the system.