Electron tunneling through indirect single barriers.

The light transfer characteristics of one-dimensional photonic crystal with single and double-barrier quantum well are studied by transfer matrix method. The results show that when the refractive index of the barrier layer is high, the transmission peaks in single-barrier quantum well of photonic crystal will be narrower and the inner localized field will be stronger, that the peak in the double-barrier is narrower than the one in the single-barrier, and also the inner localized field is stronger in the double-barrier, that with the number of period layer in the photonic crystal increasing, the inner localized field in the double-barrier well is enhanced, furthermore, the bigger the refractive index ratio between barrier and dielectric layers of well, the stronger the inner localized field in the photonic crystal quantum well is. In addition, when the periodicity of the barrier layer in the photonic crystal with a thicker refractive index increases, the inner localized field will strengthen faster, and accordingly, the transmittance of the transmission peak will decrease more quickly. Both of the strengthening and decreasing will work at the top speed when all periods in different barriers increase at the same time. While the period number of the photonic crystal in well layers increases, the inner localized fields in both single and double-barrier will increase, but their transmittances of the transmission peak will keep the same. The characteristics above can provide guidance for designing new high-quality quantum optical devices.

We analyze, within the framework of a one-band tight-binding model, the effect of diagonal disorder on the electronic states of a chainlike double-barrier quantum-well structure. Tunneling transmission probabilities together with local densities of states are evaluated in order to study quantum-size effects as a function of disorder in a quantum well.

We report strong room-temperature intersubband absorption in 80 \AA{} strain-compensated ${\mathrm{In}}_{0.84}{\mathrm{Ga}}_{0.16}{\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}\mathrm{A}\mathrm{s}/\mathrm{I}\mathrm{n}}_{0.52}{\mathrm{Al}}_{0.48}\mathrm{As}$ double-barrier quantum wells grown on InP substrates. From the multiple \ensuremath{\Gamma}-\ensuremath{\Gamma} intersubband transitions observed, it is inferred that the electron effective masses and nonparabolicity parameters for the first two subbands differ significantly from each other. For the range $k\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{6}--6\ifmmode\times\else\texttimes\fi{}{10}^{6}{\mathrm{cm}}^{\ensuremath{-}1},$ the difference in subband parameters results in a change in transition energy of about twice the value calculated for the corresponding GaAs/AlGaAs quantum well.

An asymmetric double quantum well structure consisting of a wide and a narrow quantum well separated by AlxGa1-xAs barriers of various thicknesses is used to investigate resonant and nonresonant tunneling of electrons as well as holes through a single barrier. The carrier transfer times are obtained by tracing the luminescence decay of the two quantum wells with picosecond time resolution as a function of an applied electric field. For the first time, resonant and nonresonant electron and hole tunneling times in one single structure are reported. Our results are compared with those of other groups. Idealized theoretical models cannot explain the experimental values.

A novel resonant tunneling bipolar transistor with two peaks in the output as well as the transfer characteristics is reported. The multiple peaks are obtained by sequentially quenching resonant tunneling through the ground states of a series of double-barrier quantum wells, placed in the emitter of a Ga/sub 0.47/In/sub 0.53/As n-p-n bipolar transistor, thus obtaining nearly equal peak currents and peak-to-valley ratios. The transistor exhibits current gain of about 70 at room temperature and 200 at 77 K. Peak-to-valley ratios at room temperature and at 77 K are as high as 4:1 and 20:1, respectively. The transistor has been used to design frequency-multiplier and four-bit-parity-generator circuits. A one-transistor circuit multiplies the frequencies of sawtooth and sinewave input signals by factors of three and five, respectively. The four-bit-party generator requires only one transistor, as compared to 24 needed in conventional circuits. >

The transport of photogenerated carriers perpendicular to the quantum wells in the p-i-n structure is discussed. The field-drifting resonant tunneling through the a-Si:H/a-Si/sub 1-x/C/sub x/:H double-barrier (or three-barrier) quantum wells, located at different positions of the i-layer, was studied. The room-temperature resonant-tunneling behavior is observed when the quantum well structure is embedded in the middle second of the i-layer. The results provide further evidence of quantum size effects in amorphous-silicon-based superlattice structures. >

We review our comprehensive investigations of electron and hole tunneling times between quantum wells separated by a single barrier. These studies show strong electronic and phonon resonances, strong influence of collisions and relaxation on tunneling times and provide new insights into nonresonant and resonant tunneling in semiconductor microstructures.

We report on electron and hole capture times in n-type GaAs/AlAs/Al0.3Ga0.7As double-barrier quantum well (DBQW) structures in an electric field applied perpendicular to the layers. We have measured the time-dependent photoluminescence (PL) originating from the GaAs wells and the Al0.3Ga0.7As barrier layers. The experimental capture times are obtained from least-squares fits of appropriate model functions to the observed PL transients. We have theoretically determined electron capture times for the investigated DBQWs, by calculating the electron wavefunctions and taking into account various scattering processes, including impurity scattering, optical phonon-assisted tunnelling and intervalley scattering. We find evidence that electron capture occurs by Gamma -X intervalley transfer via X-point subbands localized in the AlAs layers.

The quantum mechanical phenomenon of tunneling is of interest from fundamental as well as device points of views. Semiconductor microstructures, and in particular asymmetric double quantum well structures (a-DQWS), provide ideal systems for investigating tunneling phenomena, especially when an electric field is applied to bring various electronic levels into resonance. We first discuss various resonant and nonresonant tunneling processes for electrons and holes, including both coherent and incoherent resonant tunneling and then review recent extensive investigations of resonant and non-resonant tunneling rates of electrons and holes in asymmetric double quantum well structures using time resolved spectroscopy. We also show that cw and ultrashort pulse experiments probe different physics and that it is difficult to obtain quantitative information about resonances and resonant tunneling rates from cw experiments.

Recently, multiple quantum wells structure are often used in the laser and diode applications in order to increase their efficiency. In this structure, electron tunnelling phenomena from a quantum well to another well play a key role in electronic transport itself. Tunnelling is a quantum mechanical phenomenon where an electron is commonly represented by its wavefunction. This paper presents a numerical simulation of electron tunnelling probability on three quantum wells (quadruple barrier) Si/SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> system focusing the applied bias effect on the tunnelling probability. The tunneling probability is calculated by solving the Schrodinger's equations through potential barrier using transfer matrix method. The simulation results show the mini-band formation due to the appearance of discrete energy group. We also found that the applied bias on this structure causes the changes in tunnelling probability and discrete energy gap. Therefore, the control of voltage bias and device structure is required in order to obtain expected characteristic of multiple quantum well structure.

Tunnel nanojunctions based on inelastic electron tunneling (IET) have been heralded as a breakthrough for ultra-fast integrated light sources. However, the majority of electrons tend to tunnel through a junction elastically, resulting in weak photon-emission power and limited efficiency, which have hindered their practical applications to date. Resonant tunneling has been proposed as a way to alleviate this limitation, but photon-emissions under resonant tunneling conditions have remained unsatisfactory for practical IET-based light sources due to the inherent contradiction between high photon-emission efficiency and power. In this work, we introduce a novel approach that leverages much stronger resonant tunneling enhancement achieved by multiple metallic quantum wells, which has enabled the internal quantum efficiency to reach ∼1 and photon-emission power to reach ∼0.8 µW/µm2. Furthermore, this method is applicable with different electronic lifetimes ranging from 10 fs to 100 fs simultaneously, bringing practical implementation of IET-based sources one step closer to reality.

We have investigated the resonant tunnelling of electrons through X-valley related states in a single AlAs barrier with Si donor & doping. Under high hydrostatic pressure all the peaks observed in the differential conductance-voltage (σ-V) characteristics shift with a pressure rate of -lSmeV/kbar, which is expected for X-minima related electronic states.

The Breit–Wigner formula is exploited to calculate the tunneling transmission probability affected by longitudinal optical phonon scattering in multiple quantum wells composed of Ga1−xAlxAs compounds. A quantitative result shows that the resonance electron energy and the integrated total transmission probability through the potential barriers are not changed, while the transmission peak is reduced and the linewidth is broadened.

In this work, we have investigated magneto-transport and polarization resolved photoluminescence of a GaAs/AlGaAs resonant tunneling diode with Si delta-doping at the center of the quantum well under a magnetic field parallel to the tunnel current. Three resonant peaks were observed in the current-voltage characteristics curve (J(V)) which were associated to donor-assisted resonant tunneling, electron resonant tunneling and to phonon-­assisted resonant tunneling. The optical emission from GaAs contact layers shows evidence of highly spin-polarized two-dimensional electron and hole gases which affect the spin-polarization of carriers in the well. The quantum well photoluminescence shows strong circular polarization degrees with values up to 85% under 15T at the donor assisted resonant tunneling peak voltage. Our results can be exploited for future development of voltage-controlled spintronics devices.

A new type of field emission resonant tunneling diode has been proposed and investigated both theoretically and experimentally. The diode is based on an Si–SiOx–Si multilayer cathode containing an SiOx layer as the input potential barrier, an Si layer as the quantum well, and a vacuum layer as the output potential barrier of a double barrier quantum structure. The calculation predicted the existence of the resonant maxima (three or four depending on the input barrier height) of the current density–electric field dependencies. Frequency dependencies of the diode microwave impedance pointed to the existence of negative conductance resulting from resonant tunneling through an energy level in the quantum well (QW) at electron transit angle values in the interval from zero up to near 2π/3. Also found is a peak of negative conductance on the frequency dependence with the greatest peak value ∼57 S/cm at a frequency of 0.63 THz. The maximum upper frequency of the negative conductance band of more than 2 THz at a transit angle near 0.45π is reached when resonant tunneling occurs through the third resonant level in the QW. Experimental results confirmed the existence of the resonance peak in the investigated resonant-tunneling structure.