Barrier Resonant Tunneling Research Articles

Analytical models of transmission probabilities for electron sources

Electron emission from coated surfaces as a result of thermal, field, and photoemission effects is often described theoretically using models dependent on the Kemble approximation for the transmission probability D(k). The validity of the approximation for the simple potential profiles (rectangular, triangular, and parabolic) is examined, and generalizations with respect to the exponential of the Gamow tunneling factor and the coefficients of D(k), which are generally ignored, are examined and extended to when the barriers become wells. As a result, unity transmission probabilities (D(k)→1) with regard to both resonant tunneling barrier and reflectionless well behavior are contrasted. The adaptation of the findings to a general thermal-field-photoemission equation is considered. Consequences for the usage of general emission equations in beam optics code [e.g., Particle-in-Cell (PIC)] such as MICHELLE are discussed.

Spectral response, dark current, and noise analyses in resonant tunneling quantum dot infrared photodetectors.

Reduction of dark current at high-temperature operation is a great challenge in conventional quantum dot infrared photodetectors, as the rate of thermal excitations resulting in the dark current increases exponentially with temperature. A resonant tunneling barrier is the best candidate for suppression of dark current, enhancement in signal-to-noise ratio, and selective extraction of different wavelength response. In this paper, we use a physical model developed by the authors recently to design a proper resonant tunneling barrier for quantum infrared photodetectors and to study and analyze the spectral response of these devices. The calculated transmission coefficient of electrons by this model and its dependency on bias voltage are in agreement with experimental results. Furthermore, based on the calculated transmission coefficient, the dark current of a quantum dot infrared photodetector with a resonant tunneling barrier is calculated and compared with the experimental data. The validity of our model is proven through this comparison. Theoretical dark current by our model shows better agreement with the experimental data and is more accurate than the previously developed model. Moreover, noise in the device is calculated. Finally, the effect of different parameters, such as temperature, size of quantum dots, and bias voltage, on the performance of the device is simulated and studied.

Insights on energy selective contacts for thermal energy harvesting using double resonant tunneling contacts and numerical modeling

Energy selective electrical contacts have been proposed as a way to approach ultimate efficiencies both for thermoelectric and photovoltaic devices as they allow a reduction of the entropy production during the energy conversion process. A self-consistent numerical model based on the transfer matrix approach in the effective mass and envelope function approximation has been developed to calculate the electronic properties of double resonant tunneling barriers used as energy selective contacts in hot carrier solar cells. It is found that the application of an external electric bias significantly degrades the electronic transmission of the structure, and thus the tunneling current in the current-voltage characteristic. This is due to a symmetry breaking which can be offset using finely tuned asymmetric double resonant tunneling barriers, leading to a full recovery of the tunneling current in our model. Moreover, we model the heterostructure using electrons temperature in the emitter higher than that of the lattice, providing insights on the interpretation of experimental devices functioning in hot carrier conditions, especially regarding the previously reported shift of the resonance peak (negative differential resistance), which we interpret as related to a shift in the hot electron distribution while the maximum remains at the conduction band edge of the emitter. Finally, experimental results are presented using asymmetric structure showing significantly improved resonant properties at room temperature with very sharp negative differential resistance.

Self-Consistent Modeling of Double Resonant Tunneling Barriers Selective Contacts for Hot Carrier Solar Cells

Self-Consistent Modeling of Double Resonant Tunneling Barriers Selective Contacts for Hot Carrier Solar Cells

Proposal of a quantum ring intersubband photodetector integrated with avalanche multiplication region for high performance detection of far infrared

In this paper, a novel design of quantum ring infrared photodetector (QRIP) is proposed based on an additional avalanche multiplication region and its performance theoretically is investigated. The device consists of two intrinsic regions including: (i) quantum ring based absorption region which is responsible for absorption longer wavelength radiations and (ii) avalanche multiplication region for multiplying the generated carriers in absorption layer. Since lower electric fields are needed for absorption region to keep the dark current low and higher fields are required for multiplication region, a highly doped charge layer is used to separate absorption and multiplication regions and non-uniformly distribute the electric field. Also to further reduction of dark current, resonant tunneling barriers are embedded in absorption region to provide only a pass for optically excited electrons. Simulation results shows a higher responsivity and specific detectivity about 40A/W and 2×1010cmHz1/2/W at λ=20μm, respectively.

Quantum-dot-based single-photon avalanche detector for mid-infrared applications

A single-photon detector is presented with quantum dot (QD) layers in its absorption region. The proposed detector is a three-terminal device in which a QD-based absorption region is integrated with an avalanche multiplication region through a tunneling barrier and the applied bias of each region can be controlled separately. The mid-infrared single photons (λ=3∼5  μm) can be absorbed in QDs and the photogenerated electrons are drifted to the avalanche region to trigger an avalanche and generate an output pulse. Since the absorption region consists of doped QD layers, it is expected to have higher orders of dark count. However, by separately controlling the bias and keeping the electric field of absorption region low, the dark current of this region can be reduced. Our simulations predict a single-photon detection efficiency (SPQE) of about 0.7 at T=50  K for the proposed detector. At higher temperatures, the dark count rate increases and results in reduced SPQE. To increase the operation temperature, resonant tunneling barriers (RTB) are included in the absorption region to inhibit the thermally excited electrons from contributing to the dark current generation. Our results show that the SPQE for the RTB-based device is about 0.65 at T=77  K, which is approximately equivalent to the SPQE of the device without RTB at T=50  K.

Avalanche quantum dot-in-well long wavelength infrared photodetectors: Linear and Geiger mode operation

Employment of additional multiplication region in the structure of quantum dots-in-well (DWELL) intersubband photodetectors can be a useful alternative for amplification of the photocurrent and giving higher gain to detected optical signal. For such detector the photocurrent of DWELL detector is increased by avalanche multiplication to achieve higher responsivity and resonant tunneling barriers are used in absorption region to reduce the dark current. In this paper the linear and Geiger mode operation of proposed detector is studied for operation at λ=11μm. In linear operation, the specific detectivity (D*) is increased about one order of magnitude in comparison to experimentally reported conventional DWELL detectors. We also report the single photon detection around mid and long infrared wavelength by gated mode operation of this detector with single photon quantum efficiency of about 3%.

InAs/GaAs far infrared quantum ring inter-subband photodetector

In this paper, we presented a numerical analysis of absorption coefficient, dark current and specific detectivity for InAs/GaAs quantum ring inter-subband photodetector (QRIP). 3D Schrodinger equation was solved using finite difference method and based on effective mass approximation. Dimensions of quantum ring (QR) were considered that inter-subband transition was to be accomplished for radiations of 20 μm. Resonant tunneling (RT) barriers were designed with tunneling probability of unity for electrons with energy of 0.062 meV to lower dark current of conventional QRIP. Numerical analyses show that inclusion of RT barriers can reduce dark current for about two orders of magnitude. Furthermore, specific detectivities for conventional QRIP and RT-QRIP were calculated respectively, and results at different temperatures were compared. It is suggested that specific detectivity for RT-QRIP is one order of magnitude higher than that for conventional QRIP. It is suggested that RT barriers considerably improve the specific detectivity of conventional QRIP at different temperatures.

Numerical analysis of quantum ring intersubband photodetector for far infrared detection

A quantum ring based intersubband photodetector is designed and its optical performance is studied based on a developed theoretical model. Intersubband absorption of quantum rings is numerically calculated for two transitions, from ground state to first excited state and to continuum energy and the effects of broadening mechanisms are studied. Device show responsivity about 0.2 A/W at T = 80 K and V = 2 V. Dark current of structure with and without the resonant tunneling barriers is calculated. Specific detectivity \((D^*)\) is studied at different temperatures and peak values about \(3\times 10^{12}\,\hbox {cm Hz}^{1/2}/\hbox {W}\) is obtained at T = 50 K. Results show that inclusion of resonant tunneling barriers leads to improvement in \(D^*\) about one order of magnitude.

Quantum dot infrared photodetector with gated-mode design for mid-IR single photon detection

A novel design for a quantum dot infrared photodetector (QDIP) is proposed based on avalanche multiplication and is expected to be used as a single photon detector at mid-IR. A high field multiplication region is added to a conventional QDIP in separate absorption, charge, and multiplication structures to intensify incoming photocurrent generated in the absorption region. The absorption region of the photodetector consists of quantum dot layers that are responsible for absorption of mid-IR wavelengths. Because of higher operation voltages in gated-mode operation, resonant tunneling barriers are also included in the absorption region to prevent higher dark currents. The absorption region is designed for operation at λ=8 μm. During the gate pulse period, photo-generated electrons can trigger an avalanche and produce an output pulse. For this detector, the dark count rate (DCR) and single photon quantum efficiency (SPQE) are calculated at different temperatures. SPQE with peak of about 0.3 for T=50 K is obtained. For higher temperatures, about T=120 K, SPQE is very low due to the contribution of dark carriers generated in the quantum dot absorption region.

Quantum-Dot-Based Mid-IR Single-Photon Detector With Self-Quenching and Self-Recovering Operation

A single-photon detector based on an avalanche quantum dot IR photodetector is presented and designed for self-quenching and self-recovering operation at IR wavelength. The device consists of dot layers and resonant tunneling barriers in the absorption region. An additional layer, called the transient carrier buffer, is added to trap the backward holes. For an avalanche process, the accumulation of backward-traveling-avalanche-generated holes leads to a reduction in the electric field of the multiplication region and avalanche gain, and consequently, the detector is quenched. The detector is self-recovered by thermionic emission and tunneling currents. We study the self-quenching and self-recovery performance of the device. A detection efficiency of around 8% is obtained.

Scattering theory of nonlinear thermoelectricity in quantum coherent conductors

We construct a scattering theory of weakly nonlinear thermoelectric transport through sub-micron scale conductors. The theory incorporates the leading nonlinear contributions in temperature and voltage biases to the charge and heat currents. Because of the finite capacitances of sub-micron scale conducting circuits, fundamental conservation laws such as gauge invariance and current conservation require special care to be preserved. We do this by extending the approach of Christen and Büttiker (1996 Europhys. Lett. 35 523) to coupled charge and heat transport. In this way we write relations connecting nonlinear transport coefficients in a manner similar to Mott’s relation between the linear thermopower and the linear conductance. We derive sum rules that nonlinear transport coefficients must satisfy to preserve gauge invariance and current conservation. We illustrate our theory by calculating the efficiency of heat engines and the coefficient of performance of thermoelectric refrigerators based on quantum point contacts and resonant tunneling barriers. We identify, in particular, rectification effects that increase device performance.

Scattering Theory of Nonlinear Thermoelectric Transport

We investigate nonlinear transport properties of quantum conductors in response to both electrical and thermal driving forces. Within the scattering approach, we determine the nonequilibrium screening potential of a generic mesoscopic system and find that its response is dictated by particle and entropic injectivities which describe the charge and entropy transfer during transport. We illustrate our model analyzing the voltage and thermal rectification of a resonant tunneling barrier. Importantly, we discuss interaction induced contributions to the thermopower in the presence of large temperature differences.

Redox Molecules for a Resonant Tunneling Barrier in Nonvolatile Memory

To attain better program/erase (P/E) efficiency while maintaining retention, durable redox molecules were integrated into the flash memory gate stack to form resonant tunneling barrier by either a hybrid organic/inorganic deposition or a simple solution-based layer-by-layer (LBL) method. Compared with fullerene molecules, the proposed porphyrin has high number density and a wafer-ready LBL process. Improvement in electron retention of approximately six orders of magnitude to programming time (tR/tPE) was observed for Au nanocrystal memory with a hybrid organic-inorganic tunnel barrier. With the LBL method, the tR/tPE improved by at least two orders of magnitude for both electron and hole carriers, with the P/E cycling endurance larger than 104 cycles. Furthermore, the gate current is used to characterize the transport mechanism and study the electrical reliability of the organic layers. A better understanding of the charge storage and insulation properties of these organic barriers can improve future design integration on all-organic or hybrid molecular electronics.

Noise properties of nanoscale YBa2Cu3O7−δJosephson junctions

We present electric noise measurements of nanoscale biepitaxial YBa2Cu3O(7-x) (YBCO) Josephson junctions fabricated by two different lithographic methods. The first (conventional) technique defines the junctions directly by ion milling etching through an amorphous carbon mask. The second (soft patterning) method makes use of the phase competition between the superconducting YBCO (Y123) and the insulating Y2BaCuO5 (Y211) phase at the grain boundary interface on MgO (110) substrates. The voltage noise properties of the two methods are compared in this study. For all junctions (having a thickness of 100 nm and widths of 250-500 nm) we see a significant amount of individual charge traps. We have extracted an approximate value for the effective area of the charge traps from the noise data. From the noise measurements we infer that the soft patterned junctions with a grain boundary (GB) interface manifesting a large c-axis tunneling component have a uniform barrier and a SIS like behavior. The noise properties of soft patterned junctions having a GB interface dominated by transport parallel to the ab-planes are in accordance with a resonant tunneling barrier model. The conventionally patterned junctions, instead, have suppressed superconducting transport channels with an area much less than the nominal junction area. These findings are important for the implementation of nanosized Josephson junctions in quantum circuits.

ENGINEERING THE BARRIER OF QUANTUM DOTS-IN-A-WELL (DWELL) INFRARED PHOTODETECTORS FOR HIGH TEMPERATURE OPERATION

Reduction in the dark current and improvement in signal to noise ratio in the quantum dots in a well infrared photodetectors using resonant tunneling barriers have been demonstrated. Ultra-low dark current levels and high detectivity of 3×1010 cm.Hz1/2/W at 77K for f/2 optics has been obtained for longwave infrared detection. In another experiment, the ability to control the excited state in the DWELL has been demonstrated by systematically varying the quantum well thickness. These detectors demonstrate high operating temperature with high detectivity values, even for high operating temperatures.

Time operators in stroboscopic wave-packet basis and the time scales in tunneling

We demonstrate that the time operator that measures the time of arrival of a quantum particle into a chosen state can be defined as a self-adjoint quantum-mechanical operator using periodic boundary conditions and applied to wave functions in energy representation. The time becomes quantized into discrete eigenvalues; and the eigenstates of the time operator, i.e., the stroboscopic wave packets introduced recently [Phys. Rev. Lett. 101, 046402 (2008)], form an orthogonal system of states. The formalism provides simple physical interpretation of the time-measurement process and direct construction of normalized, positive definite probability distribution for the quantized values of the arrival time. The average value of the time is equal to the phase time but in general depends on the choice of zero time eigenstate, whereas the uncertainty of the average is related to the traversal time and is independent of this choice. The general formalism is applied to a particle tunneling through a resonant tunneling barrier in one dimension.

Resonant Tunneling Barriers in Quantum Dots-in-a-Well Infrared Photodetectors

The use of resonant tunneling (RT) barriers in the design of quantum dots-in-a-well (DWELL) infrared photodetectors is reported. The design of RT barriers for a variety of goals has been discussed. For simple DWELL designs, we demonstrate 2-3 orders-of-magnitude reduction in the dark current, with significant increase in the specific detectivity (D *) of the device. Two RT barriers are designed to selectively extract midwave and longwave components of the spectral response. We also report the use of RT barriers on strain-optimized quantum dots-in-a-double-well (DDWELL) structures to achieve very low dark current levels with peak D * of 2.9 ×1010 cm· Hz1/2 /W for a longwave infrared detection. Ability to select a particular wavelength in the spectral response is demonstrated with DDWELL architectures as well.

Wavepacket basis for time-dependent processes and its application to relaxation in resonant electronic transport

Stroboscopic wavepacket basis sets [P. Bokes, F. Corsetti, R. W. Godby, Phys. Rev. Lett., 2008, 101, 046402] are specifically tailored for a description of time-dependent processes in extended systems, such as non-periodic geometries of various contacts consisting of solids and molecules. The explanation of the construction of such a basis for two simple finite systems is followed by a review of the general theory for extended systems with continuous spectrum. The latter is further elaborated with the introduction of the interaction representation which takes full advantage of the time-dynamics built into the basis. The formalism is applied to a semi-analytical example of electronic transport through resonant tunnelling barrier in 1D. Through the time-dependent generalisation of the Landauer formula given in terms of the Fourier expansion of the transmission amplitude we analyze the temporal character of the onset of the steady-state. Various time-scales in this process are shown to be directly related to the energetic structure of the resonant barrier.

Reduction in dark current using resonant tunneling barriers in quantum dots-in-a-well long wavelength infrared photodetector

We report the use of resonant tunneling (RT) assisted barriers to reduce the dark current in quantum dots-in-a-well (DWELL) infrared photodetectors. Designed RT barriers allow energy-selective extraction of photoexcited carriers while blocking a continuum of energies. Over two orders of magnitude reduction in the dark current in the RT-DWELL device over a control sample without RT-DWELL at 77K has been demonstrated. Specific detectivity (D*) of 3.6×109cmHz1∕2W−1 at 77K at λpeak=11μm with a conversion efficiency of 5.3% was obtained in the RT-DWELL device. D* for the RT-DWELL device is five times higher than that of the control sample.