Photon-assisted Tunneling Research Articles

Room temperature operation of electro-optical bistability in the edge-emitting tunneling-collector transistor laser

Optical bistable devices are fundamental to digital photonics as building blocks of switches, logic gates, and memories in future computer systems. Here, we demonstrate both optical and electrical bistability and capability for switching in a single transistor operated at room temperature. The electro-optical hysteresis is explained by the interaction of electron-hole (e-h) generation and recombination dynamics with the cavity photon modulation in different switching paths. The switch-UP and switch-DOWN threshold voltages are determined by the rate difference of photon generation at the base quantum-well and the photon absorption via intra-cavity photon-assisted tunneling controlled by the collector voltage. Thus, the transistor laser electro-optical bistable switching is programmable with base current and collector voltage, and the basis for high speed optical logic processors.

Photon-assisted transport through a 1D-dot-graphene similar to STM model device

By using the nonequilibrium Green function method, the photon-assisted electron transport through a graphene-based device similar to STM model is studied theoretically and numerically. The device is composed of a single central site (quantum dot) modulated by an oscillating electric field, a one-dimensional quantum wire and a two-dimensional graphene sheet. Some interesting results on transmission probability and current–voltage ([Formula: see text]–[Formula: see text]) characteristics of the device are given in this paper. In the presence of an oscillating electric field, we find that besides the central two transmission peaks caused by graphene part, there appear photon-assisted peaks which are distributed on both sides of the Fermi level. The positions of the photon-assisted peaks are linear to the frequency of the oscillating electric field, and the widths of the photon-assisted peaks are relevant to the amplitude of the oscillating electric field. It is found that the current–voltage graphs exhibit step growth due to the existence of photon-assisted tunneling. We hope these results may have guidance meaning for the fabrication of optoelectronic devices.

Resonant tunneling of illuminated multi-insulator diodes

The current–voltage (I–V) characteristics of two different Metal–Insulator–Metal (MIM) diodes with three insulator layers were calculated and compared. The effect of illumination, or the photon-assisted tunneling was considered with the Tien–Gordon model. Our calculations indicate that, by carefully designing the insulating layers of the MIM diodes, the resonant tunneling phenomena can be tuned effectively in the diodes with quantum well structures. The results also show that the minimum shift of the illuminated current depends not only on the intensity of the photons incident but also on the diode structures, or the parameters of the insulators and so on.

Spin-valley resolved photon-assisted tunneling in carbon nanotube double quantum dots

We consider the photon-assisted tunneling (PAT) and the Landau-Zener-Stueckelberg (LZS) interference for double quantum dots induced electrostatically along a semiconducting carbon nanotube. An atomistic tight-binding approach and the time-dependent configuration interaction method are employed for description of the systems of a few confined electrons and holes. We reproduce the patterns of the LZS interference recently observed for the quantum double dots describing transport across hole-localized states. Moreover, we indicate that for charge configurations for which the ground-state is Pauli blocked PAT can be used for resolution of the transitions that involve spin-flip or intervalley transitions without the spin-valley conserving background signal.

Electro-optical hysteresis and bistability in the ring-cavity tunneling-collector transistor laser

Bistable devices are fundamental to digital electronics as building blocks of switches, logic gates, and memory in computer systems. We demonstrate here transistor lasers exhibiting both electrical and optical hystereses with sharp square-corner current switching and different voltage thresholds in the collector IC–VCE and optical L–VCE family of characteristics. The electro-optical hysteresis is explained by the different switching paths of electron-hole (e-h) and photon interactions involving cavity coherent and incoherent energy states employing intracavity photon-assisted tunneling at the collector junction and spontaneous/stimulated e-h recombination at the base quantum-well. The electro-optical bistability of the transistor laser possesses a unique property of voltage (field) modulation and the basis for high speed optical logic processors.

Enhancing the spin transfer torque in magnetic tunnel junctions by ac modulation

The phenomenon of spin transfer torque (STT) has attracted a great deal of interests due to its promising prospects in practical spintronic devices. In this paper, we report a theoretical investigation of STT in a noncollinear magnetic tunnel junction under ac modulation based on the nonequilibrium Green's function formalism, and derive a closed-formulation for predicting the time-averaged STT. Using this formulation, the ac STT of a carbon-nanotube-based magnetic tunnel junction is analyzed. Under ac modulation, the low-bias linear (quadratic) dependence of the in-plane (out-of-plane) torque on bias still holds, and the $\sin\theta$ dependence on the noncollinear angle is maintained. By photon-assisted tunneling, the bias-induced components of the in-plane and out-of-plane torques can be enhanced significantly, about 12 and 75 times, respectively. Our analysis reveals the condition for achieving optimized STT enhancement and suggests that ac modulation is a very effective way for electrical manipulation of STT.

Photon-assisted tunneling for sub-bandgap light detection in silicon PN-doped waveguides.

We demonstrate silicon ridge waveguide photo-detectors capable of sub-bandgap light absorption and avalanche multiplication. The proposed waveguide photo-detectors contain highly doped PN junction, where a strong electric field can generate the photon-assisted tunneling current for sub-bandgap light incidence and amplify the generated photo-current by the avalanche multiplication effect. The voltage-dependent sub-bandgap absorption coefficient and multiplication gain are experimentally evaluated for various doping configurations to find optimal photo-response with low dark currents. As a result, our representative silicon waveguide photo-detector gives sub-bandgap responsivities of ~10 and ~2 A/W under the applied reverse bias voltage of -8.3 V for near-infrared wavelengths of 1.31 and 1.52 μm, respectively. The voltage-dependent frequency photo-response is also demonstrated with theoretical verification.

Photon-Phonon-Enhanced Infrared Rectification in a Two-Dimensional Nanoantenna-Coupled Tunnel Diode

Direct conversion of infrared radiation to electrical current will dramatically impact energy recovery from low-grade heat sources. The authors present a large-area, nanoantenna-coupled tunnel diode that generates electricity from infrared radiation, with enhanced photocurrent due to impedance-matched optical-phonon resonances in the tunnel dielectric that lead to photon-assisted tunneling. This suggests exciting advances in thermal energy harvesting and near-field heat transfer.

Photon-assisted and spin-dependent shot noise in magnetic-field tunable ZnSe/Zn1−xMnxSe structures**Project supported by the National Natural Science Foundation of China (Grant No. 11574173), the National Basic Research Program of China (Grant No. 2011CB606405), and the General Program of Science and Technology Development Project of Beijing Municipal Education Commission of China (Grant No. KM201410028021).

We have investigated the photon-assisted shot noise properties in the magnetic field tunable heterostructures. Transport properties of the model structure are strongly dependent on the oscillatory field and the magnetic field. In this structure, electrons can absorb or emit one or multi-photons to reach the quasi-bound state. As a result, the transmission properties are affected considerably by photon-assisted tunneling and these features cause the nontrivial variations in the shot noise and Fano factor. It is found that the shot noise becomes spin-dependent and can be modulated not only by the magnetic field, but also by the oscillatory field. Both the spin-up and spin-down components of the shot noise can be greatly suppressed by the magnetic field, and can also be drastically enhanced by the harmonically driven field. Furthermore, with increasing external magnetic field, it is important to note that the enhanced intensity is decreased, even suppressed. These results suggest another method to suppress the shot noise via modulating the oscillatory field at a diluted-magnetic semiconductors/semiconductor structure.

Tunneling modulation of a quantum-well transistor laser

Different than the Bardeen and Brattain transistor (1947) with the current gain depending on the ratio of the base carrier spontaneous recombination lifetime to the emitter-collector transit time, the Feng and Holonyak transistor laser current gain depends upon the base electron-hole (e-h) stimulated recombination, the base dielectric relaxation transport, and the collector stimulated tunneling. For the n-p-n transistor laser tunneling operation, the electron–hole pairs are generated at the collector junction under the influence of intra-cavity photon-assisted tunneling, with electrons drifting to the collector and holes drifting to the base. The excess charge in the base lowers the emitter junction energy barrier, allowing emitter electron injection into the base and satisfying charge neutrality via base dielectric relaxation transport (∼femtoseconds). The excess electrons near the collector junction undergo stimulated recombination at the base quantum-well or transport to the collector, thus supporting tunneling current amplification and optical modulation of the transistor laser.

An analog of photon-assisted tunneling in a periodically modulated waveguide array.

We theoretically report an analog of photon-assisted tunneling (PAT) originated from dark Floquet state in a periodically driven lattice array without a static biased potential by studying a three-channel waveguide system in a non-high-frequency regime. This analog of PAT can be achieved by only periodically modulating the top waveguide and adjusting the distance between the bottom and its adjacent waveguide. It is numerically shown that the PAT resonances also exist in the five-channel waveguide system and probably exist in the waveguide arrays with other odd numbers of waveguides, but they will become weak as the number of waveguides increases. With origin different from traditional PAT, this type of PAT found in our work is closely linked to the existence of the zero-energy (dark) Floquet states. It is readily observable under currently accessible experimental conditions and may be useful for controlling light propagation in waveguide arrays.

Photon-assisted tunneling in a hybrid junction based on a quantum dot coupled to two ferromagnets and a superconductor

Photon-assisted transmission (PAT) through a three-terminal hybrid system based on a quantum dot coupled to two ferromagnetic (F) and one superconducting (S) electrodes is studied in the sub-gap regime. Linear conductance is calculated within the non-equilibrium Green function technique. The effect of PAT on the local and non-local conductances for arbitrary angles between the magnetic moments of the F electrodes is studied. A generalized formula for the Andreev reflection magnetoresistance (ARMR) is proposed and it is found that the linear conductance may be significantly modified by the photon-assisted tunneling, while ARMR remains practically unaffected by PAT. Also, the conditions for the ARMR inversion have been determined for an interplay between the transport processes occurring in the system, magnetic polarization of the F leads and the angular configuration of the magnetic moments in the F leads. It has been shown that by manipulating the a.c. amplitude and the photon angular frequency one may control the contributions to the total conductance originating from Andreev reflection, crossed Andreev reflection as well as electron tunneling between the F leads. The influence of the non-vanishing intradot Coulomb correlations on PAT in the considered three-terminal hybrid system is also discussed.

The strain effect on the Dirac electrons tunneling through the time-periodic scalar and vector barriers

The tunneling of the massless and massive Dirac particle through the strained barriers driven by the time-periodic scalar potentials and the static vector potentials is investigated, where the interrelationships among the strain, the incidence angle, the dynamic scalar potential, the magnetic field and the transmission of the Dirac particle have been discussed. In either massless or massive case, the intersection angle between the obliquely incident Dirac particle and strain determines the extent of deviation of the tunneling profiles from the strainless case. The time-periodic scalar potentials can enhance the capability of the Dirac particle to surmount the energy gap induced by the mass, reflecting quantum nature of the photon-assisted tunneling. When the magnetic field is switched on, the transmission overall presents a remarkably different profile, and decreases with the increase of the magnetic fields due to the conservation of the transverse momentum, which reduces the number of the side-band channels for tunneling.

Plasmonic Enhancement of Terahertz Devices Efficiency

This paper reviews the plasmonic effects in graphene THz photodetectors (PD) and light emitters (LE). It is demonstrated that the devices based on double graphene-layer (DGL) or multiple graphene-layer structures with the graphene layers separated by thin tunnel barrier layers have advantages over the single graphene-layer (SGL) devices. In DGLs, this advantage is due to the photon-assisted resonant tunneling when the band offset of the graphene layers is aligned to the THz photon energy. The resonant emission or absorption of the THz radiation is enhanced by the cooperative resonant excitation of the graphene plasmons leading to an extremely high gain and/or responsivity in the graphene THz device structures.

Photon-assisted tunneling in an asymmetrically coupled triple quantum dot

The gate-defined quantum dot is regarded as one of the basic structures required for scalable semiconductor quantum processors. Here, we demonstrate a structure that contains three quantum dots scaled in series. The electron number of each dot and the tunnel coupling between them can be tuned conveniently using splitting gates. We tune the quantum dot array asymmetrically such that the tunnel coupling between the right dot and the central dot is much larger than that between the left dot and the central dot. When driven by microwaves, the sidebands of the photon-assisted tunneling process appear not only in the left-to-central dot transition region but also in the left-to-right dot transition region. These sidebands are both attributed to the left-to-central transition for asymmetric coupling. Our result shows that there is a region of a triple quantum dot structure that remains indistinct when studied with a normal two-dimensional charge stability diagram; this will be helpful in future studies of the scalability of quantum dot systems.

Photon-assisted tunneling and charge dephasing in a carbon nanotube double quantum dot

We report microwave-driven photon-assisted tunneling in a suspended carbon nanotube double quantum dot. From the resonant linewidth at a temperature of 13 mK, the charge dephasing time is determined to be 280 +- 30 ps. The linewidth is independent of driving frequency, but increases with increasing temperature. The moderate temperature dependence is inconsistent with expectations from electron-phonon coupling alone, but consistent with charge noise arising in the device. The extracted level of charge noise is comparable with that expected from previous measurements of a valley-spin qubit, where it was hypothesized to be the main cause of qubit decoherence. Our results suggest a possible route towards improved valley-spin qubits.

Producing directed migration with correlated atoms in a tilted ac-driven lattice

The correlated atoms in a tilted optical lattice driven by an ac field are studied within the Hubbard model. By making use of both photon-assisted tunneling and coherent destructive tunneling effects, we can move a pair of strongly correlated atoms in the lattice via manipulating the global amplitude of the driving field. We propose a scheme for creating entanglement between the particle pair and a single particle through interacting oscillations. Our model may provide a new building block for investigating quantum computing and quantum information processing with ultracold atoms in optical lattices.

Optical rectenna operation: where Maxwell meets Einstein

Optical rectennas are antenna-coupled diode rectifiers that receive and convert optical-frequency electromagnetic radiation into DC output. The analysis of rectennas is carried out either classically using Maxwell’s wave-like approach, or quantum-mechanically using Einstein’s particle-like approach for electromagnetic radiation. One of the characteristics of classical operation is that multiple photons transfer their energy to individual electrons, whereas in quantum operation each photon transfers its energy to each electron. We analyze the correspondence between the two approaches by comparing rectenna response first to monochromatic illumination obtained using photon-assisted tunnelling theory and classical theory. Applied to broadband rectenna operation, this correspondence provides clues to designing a rectenna solar cell that has the potential to exceed the 44% quantum-limited conversion efficiency. The comparison of operating regimes shows how optical rectenna operation differs from microwave rectenna operation.

Simple Figure of Merit for Diodes in Optical Rectennas

Harvesting infrared and visible light energy using optical rectennas—diode-coupled optical antennas—is strongly dependent on the diode current–voltage characteristics. Predicting the conversion efficiency is an arduous procedure that involves calculating the efficiency by solving the nonlinear diode circuit using the theory of photon-assisted tunneling (PAT). Because of the complexity of the calculations, many rectenna diodes have been reported without indications of how well these diodes will actually function in a rectenna. To provide a quick assessment of the diodes’ usefulness in optical rectennas, we provide a figure of merit ( FOM ) that incorporates the diodes’ current–voltage and capacitance, the antenna radiation resistance, and the illumination parameters.

Photon-activated electron hopping in a single-electron trap enhanced by Josephson radiation

Using a Josephson junction interferometer (DC SQUID) as a microwave source for irradiating a single-electron trap, both devices fabricated on the same chip, we study the process of photon-assisted tunneling as an effective mechanism of single photon detection. High sensitivity down to a very small oscillation amplitude vJ∼10 nV≪Eact≲hfJ and down to low photon absorption rates Γph ∼ (1–50) Hz, as well as a clear threshold type of operation with an activation energy Eact ∼ 400 μeV, is demonstrated for the trap with respect to the microwave photons of frequency fJ ∼ (100–200) GHz. Tunable generation is demonstrated with respect to the power and frequency of the microwave signal produced by the SQUID source biased within the subgap voltage range. A much weaker effect is observed at the higher junction voltages along the quasiparticle branch of the I–V curve; this response mostly appears due to the recombination phonons.