Interband Tunneling Processes Research Articles

Many-body Green's function approach to lattice thermal transport

Recent progress in understanding thermal transport in complex crystals has highlighted the prominent role of heat conduction mediated by interband tunneling processes, which emerge between overlapping phonon bands (i.e., with energy differences smaller than their broadenings). These processes have recently been described in different ways, relying on the Wigner or Green-Kubo formalism, leading to apparently different results, which question the definition of the heat-current operator. Here, we implement a full quantum approach based on the Kubo formula, elucidating analogies and differences with the recently introduced Wigner or Green-Kubo formulations, and extending the description of thermal transport to the overdamped regime of atomic vibrations, where the phonon quasiparticle picture breaks down. We rely on first-principles calculations on complex crystals with ultralow conductivity to compare numerically the thermal conductivity obtained within the aforementioned approaches, showing that at least in the quasiparticle regime the differences are negligible for practical applications.

Pressure-induced topological superconductivity in the spin\u2013orbit Mott insulator GaTa4Se8

Lacunar spinel GaTa4Se8 is a unique example of spin–orbit coupled Mott insulator described by molecular jeff = 3/2 states. It becomes superconducting at Tc = 5.8 K under pressure without doping. In this work, we show, this pressure-induced superconductivity is a realization of a new type topological phase characterized by spin-2 Cooper pairs. Starting from first-principles density functional calculations and random phase approximation, we construct the microscopic model and perform the detailed analysis. Applying pressure is found to trigger the virtual interband tunneling processes assisted by strong Hund coupling, thereby stabilizing a particular d-wave quintet channel. Furthermore, we show that its Bogoliubov quasiparticles and their surface states exhibit novel topological nature. To verify our theory, we propose unique experimental signatures that can be measured by Josephson junction transport and scanning tunneling microscope. Our findings open up new directions searching for exotic superconductivity in spin–orbit coupled materials.

Comparative Analysis of Carrier Statistics on MOSFET and Tunneling FET Characteristics

This paper presents a comparison analysis of carrier statistics on numerical simulations of MOSFET and tunneling FET (TFET). While the MOSFET current characteristics are not sensitive to the carrier statistic utilized in the simulation, a detailed analysis is presented by inspections of the channel charge density and electric field profile. On the other hand, numerical simulations of TFETs with the Fermi–Dirac (F-D) statistics give larger current even in the sub-threshold region. It is attributed to the larger electric field across the tunnel junction between degenerated channel and heavily doped source which governs the interband tunneling process. As a result, F-D statistics should be utilized when modeling the tunneling current in TFETs.

Passivation techniques for InAs/GaSb strained layer superlattice detectors

AbstractInAs/(In,Ga)Sb Strained Layer Superlattices (SLSs) have made significant progress since they were first proposed as an infrared (IR) sensing material more than three decades ago. The basic material properties of SLS provide a prospective benefit in the realization of IR imagers with suppressed interband tunneling and Auger recombination processes, as well as high quantum efficiency and responsivity. With scaling of single pixel dimensions, the performance of focal plane arrays is strongly dependent on surface effects due to the large pixels’ surface/volume ratio. This article discusses the cause of surface leakage currents and various approaches of their reduction including dielectric passivation, passivation with organic materials (polyimide or various photoresists), passivation by overgrowth of wider bandgap material, and chalcogenide passivation. Performance of SLS detectors passivated by different techniques and operating in various regions of infrared spectrum has been compared.

Quantum tunneling through planar p–n junctions in HgTe quantum wells

We demonstrate that a p–n junction created electrically in HgTe quantum wells with inverted band structure exhibits interesting intraband and interband tunneling processes. We find a perfect intraband transmission for electrons injected perpendicularly to the interface of the p–n junction. The opacity and transparency of electrons through the p–n junction can be tuned by changing the incidence angle, the Fermi energy and the strength of the Rashba spin–orbit interaction (RSOI). The occurrence of a conductance plateau due to the formation of topological edge states in a quasi-one-dimensional (Q1D) p–n junction can be switched on and off by tuning the gate voltage. The spin orientation can be substantially rotated when the samples exhibit a moderately strong RSOI.

Electron tunneling through a planar single barrier in HgTe quantum wells with inverted band structures

We present a theoretical study on the electron tunneling through a single barrier created in a two-dimensional electron gas (2DEG) and quantum spin Hall (QSH) bar in a HgTe/CdTe quantum well with inverted band structures. For the 2DEG, the transmission shows the Fabry-Perot resonances for the interband tunneling process and is blocked when the incident energy lies in the bulk gap of the barrier region. For the QSH bar, the transmission gap is reduced to the edge gap caused by the finite size effect. Instead, transmission dips appear due to the interference between the edge states and the bound states originated from the bulk states. Such a Fano-like resonance leads to a sharp dip in the transmission which can be observed experimentally.

Klein tunneling in binary photonic superlattices

A photonic analog of Klein tunneling for a relativistic electron across a potential step, based on spatial light propagation in an engineered binary waveguide array, is proposed. Klein tunneling can be simply visualized as optical beam refraction through a step-index interface, superimposed to the superlattice, and explained as an interband tunneling process between positive-energy (electron) and negative-energy (positron) minibands of the superlattice. Inhibition of Klein tunneling for a smooth potential step is also demonstrated.

AN OPTICALLY-TRIGGERED I-RTD HYBRID THz OSCILLATOR DESIGN

A design and analysis study is presented for a new optically-triggered (OT) interband resonant-tunneling-diode (I-RTD) device that has potential for generating terahertz (THz) frequency oscillations and achieving enhanced output power levels under pulsed operation. The proposed device utilizes novel nanoscale mechanisms to achieve externally driven oscillations that consist of two phases – i.e., an initial transient phase produced by a natural Zener (interband) tunneling process and a second discharging transient phase induced by optical annihilation of stored hole-charge by externally-injected photon flux. The specific focus of this paper will be on an OT-I-RTD oscillator that utilizes In 1- x Ga x As / GaSb y As 1- y hetero-systems and the application of band-engineering to enable triggering by 1.55 μm laser technology. The paper presents performance results for the hybrid circuit design, along with a practical implementation strategy for integrating the optical triggering and an analysis of the heating induced during large signal operation.

Transfer-matrix approach to multiband Josephson junctions

We study the influence of multiple bands on the properties of Josephson junctions. In particular, we focus on the two gap superconductor magnesium diboride. We present a formalism to describe tunneling at a point contact between two $\mathrm{Mg}{\mathrm{B}}_{2}$ electrodes generalizing the transfer-matrix approach to multiple bands. A simple model is presented to determine the effective hopping amplitudes between the different energy bands as a function of the misorientation angle of the electrodes. We calculate the critical current and the current-voltage characteristics for $N\text{\ensuremath{-}}I\text{\ensuremath{-}}S$ and $S\text{\ensuremath{-}}I\text{\ensuremath{-}}S$ contacts with different orientation for junctions with both high and low transparency. We find that interband tunneling processes become increasingly important with increasing misorientation angle. This is reflected in certain features in the differential tunneling conductance in both the tunneling limit as well as for multiple Andreev reflections.

Six-bandk∙pcalculation of spin-dependent interband tunneling in strained broken-gap heterostructures under a quantizing magnetic field

We investigate spin-dependent interband magnetotunneling processes in strained broken-gap resonant tunneling structures made from InAs, AlSb, and GaSb, which are promising materials for quantum devices. InAs/AlSb/GaSb/InAs/AlSb/GaSb double-barrier structures grown on both InAs and GaSb are considered. Transmission coefficients for interband tunneling processes from individual eigenstates in the InAs emitter as well as current-voltage characteristics were calculated using a six-band k center dot p model and the scattering matrix method. We predict that due to lattice-mismatch induced strain, the interband tunneling current density for the structure grown on InAs can be one or two orders of magnitude less than that for the structure grown on GaSb. Furthermore, as a consequence of interband magnetotunneling, structures grown on different substrates yield different spin polarization of the tunneling current. It is obtained that the current spin polarization can be greater than 90%. These resonant tunneling structures can be used as spin filters in the rapidly growing field of spintronics. (Less)

Effects of lattice mismatch and bulk anisotropy on interband tunneling in broken-gap heterostructures

We have studied the effects of bulk anisotropy and the strain induced by lattice mismatch on the interband tunneling in broken-gap single-barrier InAs∕AlSb∕GaSb heterostructures and double-barrier InAs∕AlSb∕GaSb∕InAs∕AlSb∕GaSb heterostructures. We have used the eight-band k∙p model and the scattering matrix method, combined with the Burt envelope function theory, to calculate the interband transmission coefficients through the broken-gap heterostructures. We have found a noticeable anisotropy of the transmission coefficients when the magnitude of the in-plane wave vector increases to around 0.25nm−1. We have also found that the strain and the bulk anisotropy of quasiparticle dispersion produce additional peaks in the tunneling probability. For the double-barrier resonant-tunneling structures we discover a large spin splitting of the resonant-tunneling peaks caused by the lack of inversion symmetry. A strong influence of the strain induced by lattice mismatch appears in the current–voltage characteristics of the studied broken-gap heterostructures. In InAs∕AlSb∕GaSb structures the interband tunneling processes into the heavy-hole states contribute mainly to the peak current density if the sample is grown on InAs, but if the sample is grown on GaSb the interband tunneling processes into the light-hole states become the main contribution to the peak current density. As a result, the structure grown on GaSb has a much larger peak current density. This phenomenon was observed experimentally.

A novel interband-resonant tunneling diode (I-RTD) based high-frequency oscillator

A comprehensive study of the transport dynamics associated with electron- and hole-charge residing within a type-II AlGaSb/InAs/InGaSb double-barrier heterostructure is presented. These studies demonstrate an intrinsic instability within this type of resonant tunneling diode (RTD) that is initiated by an interband tunneling process. This novel interband-RTD (I-RTD), based upon staggered-bandgap heterostructures, is shown to offer a completely new avenue for the realization of very high-frequency sources. Specifically, this I-RTD device is shown to admit hole generation and discharging processes leading to repetitive cycles in electron current that constitute steady-state oscillatory behavior. Initial studies of non-optimized structures predict impressive figures of merit for oscillation frequencies (e.g., ∼300 GHz) and output powers (e.g., >2 mW) and suggest that the I-RTD is a promising new device for implementation as a terahertz (THz) frequency oscillator. Furthermore, these studies suggest that strategic engineering of the interband tunneling and charge accumulation processes may allow for significant latitude in controlling the performance of this oscillator concept at very high-frequencies.

Negative Differential Resistance Behavior in Delta‐Doped AlInP Structure Grown by MOCVD

An AlInP delta‐doped schottky diode exhibiting negative differential resistance (NDR) behavior is demonstrated for the first time. The NDR characteristics with a peak to valley ratio of 5.5 and peak current density of 1KA/cm2 were achieved at room temperature. In addition, the maximum available power is estimated up to 5W/cm2 . The mechanism for such performance is phenomenologically analyzed by the combination of resonant interband tunneling (RIT) and thermionic emission processes associated with tunneling effect on the metal‐semiconductor (MS) interface.

Peak Voltage Insensitivity to Quantum Well Width in Resonant Interband Tunneling Diodes

AbstractWe have investigated the peak voltage (Vp) in InAs/A1Sb/GaSb/A1Sb/InAs double-barrier resonant interband tunneling (DBRIT) diodes with various GaSb well widths (Lw). After eliminating the voltage drop resulting from parasitic resistance included in the measured peak voltage (Vpm), we found that the intrinsic peak voltage (Vpint) was almost insensitive to Lw and had a small, and virtually constant value (∼ 60 mV) at Lw, ranging from 10 to 30 monolayers. This insensitivity contrasts with the peak voltage of the conventional resonant tunneling diodes with intraband tunneling, which is sensitive to changes in Lw. This insensitivity can be explained by the fact that Vpint in Sb-based BDRIT diodes is affected by the occupied states in the collector rather than by the resonance level itself in the interband tunneling process.

Self-consistent modeling of the current–voltage characteristics of resonant tunneling structures with type II heterojunctions

We present a model and results of self-consistent calculation of current–voltage (I–V) characteristics of the InAs/AlSb/InAs, InAs/AlSb/GaSb resonant tunneling structures with type II heterojunctions. The different current components, charge accumulation in the quantum well and quasi-Fermi level variation in contacts and spacers due to the drift-diffusion processes, are taken into account. The kp band model is used to describe the interband and intraband tunneling processes. The transfer Hamiltonian approach is employed to obtain the resonant tunneling current density and charge density in the quantum well. A good quantitative agreement with the experiment is obtained for both structures including the agreement for the values of peak-to-valley (P/V) current ratio.

The "gated-diode" configuration in MOSFET's, a sensitive tool for characterizing hot-carrier degradation

This paper describes a new measurement technique, the forward gated-diode current characterized at low drain voltages to be applied in MOSFET's for investigating hot-carrier stress-induced defects at high spatial resolution. The generation/recombination current in the drain-to-substrate diode as a function of gate voltage, combined with two-dimensional numerical simulation, provides a sensitive tool for detecting the spatial distribution and density of interface defects. In the case of strong accumulation, additional information is obtained from interband tunneling processes occurring via interface defects. The various mechanisms for generating interface defects and fixed charges at variable stress conditions are discussed, showing that information complementary to that available from other methods is obtained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Theory of interband tunneling in crystals with impurities

A general theory is presented for the intraband and interband processes of electrons in a crystal with static impurities in a strong electric field. The interband tunneling processes, both the impurity-assisted and the Zener tunneling (and its modification by the impurities), are examined in detail. For the case of tunneling from a fully occupied band, the dependence of the tunneling rate on the electric field is shown in both cases to exhibit a steady term and some oscillatory terms, in agreement with recent experimental findings.

The negative differential resistance behavior in delta-doped GaAs structure due to resonant interband tunneling

A GaAs delta-doped tunneling diode having a δn+-i-δp+-i-δn+ structure is investigated. A negative differential resistance behavior with peak-to-valley ratio as high as 3.1 and a peak current density of 3 kA/cm2 is exhibited when the device is operated at room temperature. It becomes resistor-like at the temperature of 77 K. Theoretical analysis, based on envelope wave function approximation, indicates that the resonant interband tunneling process is responsible for room-temperature characteristics, while the band-gap widening effect is responsible for low-temperature behavior. Furthermore, the dependence of device performance on such structure parameters as doping level, and the physical dimension of the delta-doped region, etc., is discussed, and found to agree well with experimental results.

Quantization effect on capacitance-voltage and current-voltage characteristics of an InAs/AlSb/GaSb interband tunneling diode

Capacitance-voltage measurements were performed on the InAs/AlSb/GaSb interband tunneling diode at various frequencies. Theoretical analyses using a self-consistent Schrödinger–Poisson solver were found in agreement with the experimental results under the forward-bias condition. The quantization energy of each subband of the electron in the InAs accumulation region is used to predict the tunneling current cutoff voltage in agreement with that of the current-voltage measurements. Therefore, the cutoff of the interband tunneling process is mainly caused by the crossover of the electron subband energy in the InAs conduction band with respect to the valence band of the GaSb electrode due to the increased external bias voltage.