Hole Tunneling Research Articles

Loop quantum gravity with optimal control path integral, and application to black hole tunneling

This paper presents a novel path integral formalism for Einstein's theory of gravitation from the viewpoint of optimal control theory. Despite its close relation to the well-known variational principles of physicists, optimal control turns out to be more general. Within this context, a Lagrangian different from the Einstein-Hilbert Lagrangian is defined. Einstein field equations are recovered exactly with variations of the new action functional. The quantum theory is obtained using Ashtekar variables and the loop scalar product. By means of example, the tunneling process of a black hole into another black hole or into a white hole is investigated with a toy model.

Yb/WO3/Yb back to back Schottky barriers designed as voltage controlled rectifiers and as microwave resonators

Herein, 𝑝 −WO3 thin films coated onto ytterbium thin film substrates are used as active layers to fabricate a back to back Schottky (BBS) barriers. The Schottky contacts and the tungsten oxide active layers are grown by the thermal evaporation technique under a vacuum pressure of 10-5 mbar. The films are structurally, morphologically, optically and electrically characterized. The physical nature of the grown 𝑝 −WO3 layers is amorphous comprising excess oxygen in its composition. Electrically, the BBS devices displayed a biasing dependent current rectification ratio confirming the tunneling type of Schottky barriers. The current conduction are dominated through tunneling barriers of height of ~0.80 eV. The barriers allow hole tunneling within energy barriers of widths of ~45 nm and of 300 nm under reverse and forward biasing conditions, respectively. In addition, the impedance spectroscopy measurements have shown the ability of wide tunability of the resistance and capacitance of the devices resulting in a microwave cutoff frequency exceeding 2.0 GHz. The resistive and capacitive features of the devices in addition to the microwave cutoff frequency spectra nominate the Yb/𝑝-WO3/Yb BBS devices for use as microwave resonators suitable for 4G/5G technologies.

Accelerating Photogenerated Hole Tunneling through Passivation Layers via Reducing Interplanar Spacing for Efficient and Stable Perovskite Solar Cells.

Interfacial passivation engineering plays a crucial role in the explosive development of perovskite solar cells (PSCs). However, previous studies on passivation layers mainly focused on the defect-passivation mechanism rather than the interfacial charge transport efficiency. Here, by precisely tuning the interplanar spacing of the ammonium iodide passivation layer, we elucidate the promoting effect of the reduced interplanar spacing of the passivation layer on the photogenerated hole tunneling efficiency at the interface of the hole transport layer and perovskite. Compared with the commonly used phenethylammonium iodide passivation layer with a wider interplanar spacing, 2-chlorobenzylammonium iodide with a narrower interplanar spacing can help break through the thickness limitation of the passivation layer, thus showing a better comprehensive passivation effect. Therefore, we demonstrate photovoltaic devices with an enhanced fill factor (FF) and open-circuit voltage (VOC), which yield a high power conversion efficiency (PCE) of up to 23.1%. We thus identify an efficient scheme to achieve optimal passivation conditions for high-performance PSCs.

Role of Intra‐Band Relaxation of Holes and Tunneling of Electrons in Carrier Relaxation in AlGaAs/GaAs Quantum Well

The role of intra‐band hole relaxation and tunneling of electrons in the carrier relaxation in Al0.7Ga0.3As/GaAs quantum well (QW) is studied by performing pump‐probe transient reflectivity measurements with a femtosecond laser at room temperature. The ultrafast optical response of the QW sample is measured with an aim of understanding various ultrafast processes occurring on the time scale of ∼100 fs to 10 ps. Carriers are injected into the QW layer via a resonant photoexcitation of electron–hole pairs enabling a sharp rise of the signal. Carrier relaxation inside QW is dominated by non‐radiative processes like phonon‐mediated intra‐band relaxation of holes and tunneling of electrons out of the QW plane and their subsequent capture by the midgap states in the AlGaAs barrier. Subsequent to the initial thermalization within 100 fs, carrier relaxation is mainly driven by the tunneling of electrons and trapping by the midgap states over a time scale of 3–8 ps. In between, photoexcited holes are seen to relax from light to heavy hole states of QW within 1–2 ps, leading to a delayed rise of transient reflectivity signal. Systematic efforts are made to isolate various contributions which showed phonon re‐absorption leading to saturation effect in intraband relaxation.

Biexciton and trion dynamics in InP/ZnSe/ZnS quantum dots.

Transient absorption (TA) and time-resolved photoluminescence (PL) spectroscopies have been used to elucidate the hole tunneling and Auger dynamics in biexcitons and negative trions in high-quality InP/ZnSe/ZnS quantum dots (QDs). In a previous paper [Nguyen et al., J. Phys. Chem. C 125, 15405-15414 (2021)], we showed that under high-intensity photoexcitation, two types of biexcitons are formed: those having two conduction band electrons and two valence band holes (designated as an XX state) and those having two conduction band electrons, one valence band hole, and an additional trapped hole (designated as an XT state). In the present paper, we show that both types of biexcitons can undergo Auger processes, with those of the XT state being a factor of four to five slower than those of the XX state. In addition, the trapped holes can undergo tunneling into the valence band, converting an XT state to an XX state. The relative amplitudes of the fast (XX) and slow (XT) components are different in the TA and PL kinetics, and these differences can be quantitatively understood in terms of oscillator strengths and electron-hole overlap integrals of each state. XT to XX hole tunneling rates are obtained from the comparison of the XT state lifetimes with those of the negative trions. This comparison shows that the tunneling times decrease with decreasing core size and shell thickness. These times are about 2ns for the thinnest shell red-emitting QDs and decrease to 330ps for QDs that luminesce in the yellow.

Highly sensitive photomultiplication type polymer photodetectors by manipulating interfacial trapped electron density

Photomultiplication type polymer photodetectors (PM-PPDs) are successfully achieved via interfacial trap-assisted hole tunneling injection from external circuit. The external quantum efficiency (EQE) of PM-PPDs is mainly determined by the number of injected holes from external circuit and flowing across the devices. Although the trapped electron density near Al electrode can be increased for efficient hole tunneling injection by decreasing the thickness of active layers, which also makes the PM-PPDs vulnerable to breakdown. A smart strategy is firstly proposed to obtain large EQE values by decreasing the thickness of active layers and keep excellent withstanding large bias characteristic of PM-PPDs by using wide bandgap polymer poly-TPD as buffer layer. The optimal double layered ternary PM-PPDs were obtained with 40 nm poly-TPD as buffer layer and 90 nm P3HT:PBDB-T:PC61BM (80:20:2, wt/wt/wt) as active layers, exhibiting a rather large EQE value of 21400% and specific detectivity of 1.0 × 1013 Jones at 430 nm under −8 V bias. This work indicates that inserting wide bandgap and high hole mobility material as buffer layer should be an efficient strategy to prepare highly sensitive PM-PPDs, benefiting from the increased hole tunneling injection from external circuit and efficient hole flowing across the devices.

An InGaN/SiNx/Si Uniband Diode Photodetector

A novel self‐powered InGaN/SiNx/Si uniband diode photodetector (PD) is introduced. The full band structure is first constructed from the transition of direct tunneling to Fowler‐Nordheim tunneling of holes through the ultrathin SiNx interlayer at forward bias in the dark. Basis is the alignment of the n‐InGaN conduction band with the p‐Si valence band at zero bias. Under illumination, the photocurrent, responsivity, and bandwidth for the self‐powered PD at zero bias indicate two distinct operation modes (i) for longer and (ii) for shorter wavelengths of incident light. The two modes involve (i) absorption in Si and electron tunneling through the SiNx interlayer and (ii) absorption in InGaN and hole transport across the SiNx interlayer. The noise is considerably larger in operation mode (i) than in operation mode (ii). This is attributed to the presence or absence of energy barriers for electron and hole transport in PD operation. Hence, noise is introduced as an independent parameter to discriminate between longer and shorter wavelength regions in dual‐wavelength photodetection.

Low frequency Compressional modes in degenerate semiconductor plasmas

Properties of low frequency compressional electromagnetic wave pulse in a magnetized semiconductor hole-electron plasma, are investigated. The quantum mechanical effects such as Fermi pressure, quantum tunneling and exchange-correlation potential of inertialess electrons, inertial holes and stationary charged ion particulates are considered in the presence of the magnetic field. A new type of dispersion relation is derived for low-frequency compressional waves by employing quantum magneto-hydrodynamic model and Maxwell equations; the dispersion relation is then analyzed for parallel, perpendicular and oblique propagation of compressional electromagnetic wave pulse to the external magnetic field direction. We have analyzed the obtained dispersion relations numerically, for different semiconductor plasma such as GaAs, GaSb and, GaN, the graphs shows that the frequency of compressional electromagnetic wave pulse decreases with increase of electron-hole density concentration, whereas the frequency increases with the increase of angle of propagation compressional electromagnetic wave pulse. Our results are applicable to understanding the dynamics of semiconductor plasma to produce high power, high band-width devices in contrast to the existing gas plasma devices. Keywords: degenerate semiconductor plasma, quantum mechanical effects, compression electromagnetic wave, gas plasma device.

High-densities of free holes in homoepitaxial n-GaN induced by fluorine-plasma ion implantation

In this work, fluorine plasma ion implantation is used to induce high densities of free holes in homoepitaxial n-GaN for the first time, as evidenced by electroluminescence and p-n junction rectification. F+ ions implanted into the near-surface layer capture electrons from shallow bulk donors, bending the band upward until a high density of free holes is induced at the valence band maximum, and surface donors, depinning the Fermi level to form p-type ohmic contact. Free holes tunnel from the metal into states at the valence band maximum, where they form a conductive p-type channel, benefitting the development of GaN-based junction devices.

Calculating the Effect of AlGaN Dielectric Layers in a Polarization Tunnel Junction on the Performance of AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes.

In this work, AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs) with AlGaN as the dielectric layers in p+-Al0.55Ga0.45N/AlGaN/n+-Al0.55Ga0.45N polarization tunnel junctions (PTJs) were modeled to promote carrier tunneling, suppress current crowding, avoid optical absorption, and further enhance the performance of LEDs. AlGaN with different Al contents in PTJs were optimized by APSYS software to investigate the effect of a polarization-induced electric field (Ep) on hole tunneling in the PTJ. The results indicated that Al0.7Ga0.3N as a dielectric layer can realize a higher hole concentration and a higher radiative recombination rate in Multiple Quantum Wells (MQWs) than Al0.4Ga0.6N as the dielectric layer. In addition, Al0.7Ga0.3N as the dielectric layer has relatively high resistance, which can increase lateral current spreading and enhance the uniformity of the top emitting light of LEDs. However, the relatively high resistance of Al0.7Ga0.3N as the dielectric layer resulted in an increase in the forward voltage, so much higher biased voltage was required to enhance the hole tunneling efficiency of PTJ. Through the adoption of PTJs with Al0.7Ga0.3N as the dielectric layers, enhanced internal quantum efficiency (IQE) and optical output power will be possible.

Influences of Exit Advance Guide Signs on the Trajectory and Speed of Passenger Cars in Highway Tunnels

The driving behavior in highway tunnels is more complicated than that in regular roadbed sections because the former is usually affected by black and white hole effects, tunnel clearance, and bad illumination. Unfortunately, the current Chinese criteria and the Uniform Traffic Control Equipment Manual (MUTCD) 2009 guidelines provide no clear method for setting exit advance guide signs in highway tunnels. Hence, a driving simulator-based experiment was conducted in the current study to analyze the effects of exit advance guide signs on the trajectory, speed, and acceleration of passenger cars in a highway tunnel under three different service levels. It was found that when the service level is first service level, second service level, and third service level, the setting of the exit advance guide signs made the initial transverse location of the vehicle from the tunnel exit advance by 13.39%, 21.20%, and 5.73%, the lane change distance is shortened by 6.34%, 20.18%, and 15.34%, the average speed is decreased by 1.44%, 2.40%, and 0.08%, and the acceleration is decreased to −0.10 m·s−2, −0.11 m·s−2, and −0.06 m·s−2. Thus, the exit guide signs in the tunnel played a certain optimization role in improving the traffic flow state of the section and reducing the traffic accident rate.

An Enhanced Charge Carrier Separation in a Heterojunction Solar Cell with a Metal Oxide

A model of charge carrier transport in heterojunction solar cells composed of a solar light‐absorbing semiconductor and a wide‐bandgap semiconducting metal oxide is proposed. It describes an electric field in the semiconductor originating from the difference in the electron work functions between the two contacting materials, an enhanced hole separation by this field, and subsequent trap‐assisted tunneling of holes through the semiconducting oxide. The model predicts a dramatic influence of the donor concentration in the semiconductor, trap parameters in the oxide, and ideality factor of the semiconductor/oxide heterojunction on the performance of the cell. The efficiency of the solar energy harvesting by MoO x /n‐Si solar cells is calculated to reach 23% of the donor concentration in Si of 1018 cm−3 at a limited hole current density. It is predicted to be reduced to 16−18% when donor concentration is in the range of 1015−1016 cm−3. The numerical predictions agree well with experimental data, at least for donor concentrations in Si below 1018 cm−3, confirming suitability of the model for heterojunction solar cells composed of other semiconductors and semiconducting metal oxides.

Molecular electronics behaviour of L-aspartic acid using symmetrical metal electrodes.

Protein-based electronics is one of the growing areas of bio-nanoelectronics, where novel electronic devices possessing distinctive properties are being fabricated using specific proteins. Furthermore, if the bio-molecule is analysed amidst different electrodes, intriguing properties are elucidated. This research article investigates the electron transport properties of L-aspartic acid (i.e. L-amino acid) bound to symmetrical electrodes of gold, silver, copper, platinum and palladium employing NEGF-DFT approach using self-consistent function. The theoretical work function of different electrodes is calculated using local density approximation and generalized gradient approximation approach. The calculated work function correlates well with the hole tunneling barrier and conductance of the molecular device, which further authenticate the coupling strength between molecule and electrode. Molecule under consideration also exhibits negative differential resistance region and rectification ratio with all the different electrodes, due to its asymmetrical structure. The molecular device using platinum electrodes exhibits the highest peak to valley ratio of 1.38 and rectification ratio of 3.20, at finite bias. The switching characteristics of different molecular device are justified with detailed transmission spectra and MPSH. These results indicate that L-aspartic acid and similar biomolecule can be vital to the growth of Proteotronics.

Perovskite Photovoltaic Devices with Carbon‐Based Electrodes Withstanding Reverse‐Bias Voltages up to –9 V and Surpassing IEC 61215:2016 International Standard

One of the key challenges of perovskite photovoltaics (PV) is the long‐term stability. Although efforts are made to improve the lifetime of perovskite PV devices, their degradation under reverse‐bias conditions is barely addressed. Herein, perovskite solar cells with carbon‐based electrodes are presented which demonstrate superior resilience against reverse‐bias‐induced degradation. Although their breakdown voltage is identified to be at approximately −3.6 V, cells do not degrade until the applied reverse‐bias exceeds −9 V. Two main degradation mechanisms are identified: 1) iodine loss due to hole tunneling into perovskite, which takes place even at low reverse‐bias but decomposes the perovskite only after long time durations; and 2) rapid heating at large reverse‐bias leading to formation of PbI2, which starts at shunts and then follows the path of the least resistance for the cell current, which is primarily influenced by the electrode sheet resistances. Finally, perovskite solar modules with carbon‐based electrodes are demonstrated, which are subjected to a “hotspot” test described in the IEC 61215:2016 international standard at an accredited module testing laboratory. Passing this accelerated test for the first time confirms the superior stability of perovskite PV devices with carbon‐based electrodes and highlights their large industrialization potential.

Low Optical Writing Energy Multibit Optoelectronic Memory Based on SnS2 /h-BN/Graphene Heterostructure.

With the rapid development of artificial intelligence and neural network computing, the requirement for information storage in computing is gradually increasing. Floating gate memories based on 2D materials has outstanding characteristics such as non-volatility, optical writing, and optical storage, suitable for application in photonic in-memory computing chips. Notably, the optoelectronic memory requires less optical writing energy, which means lower power consumption and greater storage levels. Here, the authors report an optoelectronic memory based on SnS2 /h-BN/graphene heterostructure with an extremely low photo-generated hole tunneling barrier of 0.23eV. This non-volatile multibit floating gate memory shows a high switching ratio of 106 and a large memory window range of 64.8V in the gate range ±40V.And the memory device can achieve multilevel storage states of 50 under a low power light pulses of 0.32nW and small light pulse width of 50ms. Thanks to the Fowler-Nordheim tunneling of the photo-generated holes, the optical writing energy of the optoelectronic memory has been successfully reduced by one to three orders of magnitude compared to existing 2D materials-based systems.

Pressure effect on spin-resonant tunneling of holes in CdTe/Cd1-xMnxTe double-barrier heterostructure

Light Hole (LH) and Heavy Hole (HH) transmission, spin polarization and dwell time are theoretically studied in CdTe/CdMnTe heterostructures for different pressures. The transfer matrix method is used to find the transport properties taking Dresselhaus spin-orbit coupling into account. Sharp resonance peaks with high transmission probability are obtained for HH. A possibility to manipulate the spin-polarized dwell time of holes in this heterostructure using pressure is inferred from the results.

Intertube Excitonic Coupling in Nanotube Van der Waals Heterostructures

AbstractStrong intertube excitonic coupling is demonstrated in 1D van der Waals heterostructures by examining the ultrafast response of radial C/BN/MoS2 core/shell/skin nanotubes to femtosecond infrared light pulses. Remarkably, infrared excitation of excitons in the semiconducting carbon nanotubes (CNTs) creates a prominent excitonic response in the visible range from the MoS2 skin, even with infrared photons at energies well below the bandgap of MoS2. Via classical analogies and a quantum model of the light–matter interaction these findings are assigned to intertube excitonic correlations. Dipole–dipole Coulomb interactions in the coherent regime produce intertube biexcitons, which persist for tens of femtoseconds, while on longer timescales (>100 ps) hole tunneling—from the CNT core, through the BN tunnel barrier, to the MoS2 skin—creates intertube excitons. Charge transfer and dipole–dipole interactions thus play prominent roles on different timescales, and establish new possibilities for the multi‐functional use of these new nanoscale coaxial cables.

Spin-resonant tunneling in CdTe/Cd1-xMnxTe double-barrier heterostructure with zero external field: Effect of in-plane wave vector

The tunneling of light hole (LH) and heavy hole (HH) in CdTe/Cd1-xMnxTe double-barrier heterostructure with Dresselhaus spin-orbit interaction is studied. The effect of in-plane wave vector on barrier transparency, polarization efficiency and dwell time is theoretically analyzed. The in-plane wave vector increases the polarization efficiency of LH and HH. The enhanced spin-separation is achieved at high value of in-plane wave vector. The dwell time of LH and HH is also analyzed as a function of in-plane wave vectors.

Employing liquid crystal material as regulator to enhance performance of photomultiplication type polymer photodetectors

Photomultiplication type polymer photodetectors (PM-PPDs) were achieved with PBDB-T:BTPV-4F (98:2, wt/wt) as blend active layer based on a sandwich structure. Isolated electron traps are formed due to the rather less BTPV-4F surrounded by PBDB-T in blend active layers. Trapped electrons in BTPV-4F near Al electrode will induce interfacial band bending for hole tunneling injection into blend active layers. The tunneling injected holes will be transported along the channels formed by PBDB-T in blend active layers, photomultiplication phenomenon will be obtained when the number of holes crossing through blend active layers is larger than that of incident photons per unit time. Liquid crystal material BTR was selected as regulator to adjust PBDB-T molecular arrangement for improving hole mobility in blend active layers, leading to optimized performance of PM-PPDs. Optimal PM-PPDs were obtained with PBDB-T:BTR:BTPV-4F (89:9:2, wt/wt/wt) as blend active layer. The external quantum efficiency (EQE) values of optimal PM-PPDs are 1.5 times that of PM-PPDs based on PBDB-T:BTPV-4F (98:2, wt/wt) in the whole spectral response range under −10 V applied bias. The EQE of optimal PM-PPDs can be markedly improved by increasing applied bias, which is improved from 600% to 19,300% at 660 nm with applied bias increased from −10 to −20 V. The responsivity of optimal PM-PPDs arrives to 102 A W−1 at 660 nm under −20 V applied bias.

Highly Sensitive Narrowband Photomultiplication‐Type Organic Photodetectors Prepared by Transfer‐Printed Technology

AbstractNarrowband photomultiplication‐type organic photodetectors (PMOPDs) are realized with poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) as the optical field adjusting (OFA) layer and transfer‐printed P3HT: [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) (50:1, w/w) as the photomultiplication (PM) layer. The thickness of the OFA layers is adjusted to optimize interfacial trapped electron distribution and density, which determines the external quantum efficiency (EQE) and spectral response range of PMOPDs. Narrowband PMOPDs with 2.5 µm thick P3HT as the OFA layer exhibit two narrow response peaks at 350 and 660 nm, and the corresponding EQE values at 350 and 660 nm are 180% and 760% under an applied bias of −20 V. A wide bandgap polymer poly[N,N′‐bis(4‐butylphenyl)‐N,N′‐bis(phenyl)benzidine] (P‐TPD) is deliberately incorporated into OFA layer for adjusting interfacial trapped electron distribution near Al electrode. Narrowband PMOPDs exhibit only one response peak at 660 nm with the enhanced EQE value of 1120% under the same bias. The enhanced EQE of PMOPDs with P‐TPD is primarily attributed to the increased hole tunneling injection and transport, which can be ascribed to the enhanced trapped electron density near the Al electrode and the improved hole mobility, respectively. Clearly resolved images can be obtained from the imaging system with the narrowband PMOPDs as sensing pixel without any current preamplifier, indicating the promising potential of PMOPDs in imaging sense.