Resonant Tunneling Structures Research Articles

In situ optical diagnostics of growing surfaces in the process of nanoheterostructure fabrication

It is demonstrated that in situ reflectance and reflectance-anisotropy measurements can be used as efficient real-time monitoring tools for all stages of the growth of heterostructures with ultrathin (few-monolayer) GaAs and AlAs layers. Changes in the layer composition at normal GaAs/AlAs interfaces in the active region of resonant-tunneling diode structures are detected with a thickness resolution on the order of one monolayer. Resonant-tunneling diodes with a peak-to-valley ratio of 3.3 and peak current density of 6.6 × 104 A/cm2 are fabricated.

Purely discrete expansion of the reflection amplitude involving resonant states

We obtain, using an auxiliary function that possesses real poles located on the real k axis, a purely discrete expansion involving resonant states of the reflection amplitude for scattering by an arbitrary potential of finite range. This also includes a corresponding expansion for the continuum wave solution along the internal interaction region. Together with the previous results for the transmission region, the above results allow us to obtain purely discrete expansions for the continuum wave solutions along the full line. Our findings are exemplified by calculations on a quadruple barrier resonant tunneling structure and are indistinguishable from exact numerical calculations. The obtained results are relevant for studies on quantum transients in time-dependent scattering.

Formation of nanoelectrostatic quantum dots and two-dimensional subbands by the random potential of Mn donors in p-i-n resonant tunneling heterosystems

The influence of the random potential of Mn impurities in p-i-n resonant tunneling structures on the electronic spectrum has been studied. The possibility of the formation of zero-dimensional states in nanoelectrostatic quantum dots, as well as two-dimensional subbands in the region of GaAs quantum well, by the minima of this potential has been shown.

Phase-breaking effects in double-barrier resonant tunneling diodes with spin-orbit interaction

Several recent theoretical studies showed that the spin-orbit interaction in narrow gap InGaAs/InAlAs double-barrier resonant tunneling structures might yield a highly spin-polarized current in the ballistic limit. In this paper, a nonequilibrium Green’s function model is used to examine the effect of phase-breaking on the spin-dependent transport of carriers. The scattering is described as a local interaction with a bath of scatterers and treated in the self-consistent first Born approximation. Elastic and inelastic scatterers, with scattering strengths that cause a few millielectron volt broadening of quasibound states, have been found to significantly reduce the spin polarization. The magnitude of spin polarization has been found to be dominantly determined by the quasibound state broadening, while the interaction details are not significant.

NEW POSSIBILITIES FOR OBTAINING STEEPLY NONLINEAR CURRENT–VOLTAGE CHARACTERISTICS IN SOME SEMICONDUCTOR STRUCTURES

Electronic processes in a semiconductor system consisting of some resonant tunneling structures, built in the depletion region of a Schottky barrier, are investigated. It is shown that the Schottky barrier can block or unblock the resonant tunneling current effectively. Tunneling processes do reveal the coherent character. Sharply nonlinear current–voltage characteristics are observed for both the forward and the reverse branches.

Terahertz generation based on an optically pumped ballistic electron wave swing device

Terahertz (THz) signals can be generated by the periodic motion of ballistic electron bunches inside a quantum well cavity surrounded by two asymmetric resonant tunneling structure implemented in an InAlAs/InGaAs heterostructure. The electron bunches are produced in an adjacent active quantum well by optical excitation with a femtosecond laser pulse, and transferred into the cavity by resonant tunneling. The device contains also a superlattice that eliminates the electrons, which exit the cavity in the direction of the active quantum well. In consequence, the device output consists of a train of ultrashort pulses, of less than 100 fs, which preserve their coherence. Electrical signals up to few tens of THz can be obtained, depending on the resonant filter or antenna placed at the end of the device.

Resonant Tunneling in III-Nitrides

Wide-bandgap semiconductors can sustain high temperatures and high power operation in various important applications such as transistors, light-emitting diodes, and lasers. Although in embryonic stage, one can expect such a resilience in GaN resonant tunneling diodes (RTDs) and superlattices as well with distinct applications. Because of the negative differential conduction, the double barrier resonant tunneling structures could be the basis for new high-power coherent microwave sources operating in W-band and terahertz. In this paper, recent progress in wide-bandgap semiconductor RTDs is discussed.

A quantum transport model for the double-barrier nonmagnetic spin filter

A model for calculating the current and spin polarization in a double-barrier InGaAs resonant tunnelling structure is described with the aim to account for phase-breaking scattering. It is based on the nonequilibrium Green's function method with both elastic and inelastic (LO-phonon) scattering described within the self-consistent first Born approximation. It has been found that the maximum current spin polarization of around 0.4 in the ballistic limit decreases to around 0.1 for scattering transport with scattering-induced broadening of quasi-bound states of around 4meV.

Electronic Conductivity in Open Cylindrical Two-Barrier Symmetric Resonance Tunnel Structure

The theory of resonance energies and widths of electron quasi-stationary states and electronic conductivity in open cylindrical two-barrier symmetric resonance tunnel structure is developed. The complete Schrodinger equation is solved within the model of effective masses for rectangular potential wells and barriers. Interaction between electrons and electromagnetic field was taken into account using the approximation of the small signal. The calculations of spectral parameters are performed for In0.53Ga0.47As/In0.52Al0.48As resonance tunnel structure. The dependences of conductivity on the energy of mono-energy electrons beam falling at the system and electromagnetic field energy absorbed or emitted by the system are obtained and analyzed. The relation between experimentally measured parameters of conductivity and resonance widths of electron quasi-stationary states in open resonance tunnel structure is established.

Proposal for efficient generation of spin-polarized current in silicon

We propose a spin-dependent resonant tunneling structure to efficiently inject spin-polarized current into silicon. By means of a heavily doped polycrystalline Si between the ferromagnetic metal and Si, the Schottky barrier resistance is reduced and consequently the tunneling current density is raised. The small Fermi sea of the charge carriers in Si focuses the tunneling electrons to the resonant spin states within a small region of transverse momentum in the ferromagnet which creates the spin polarization of the current.

Pressure effect study on the I–V property of the GaAs-based resonant tunnelling structure by photoluminescence measurement

This paper discusses the I–V property of the GaAs-based resonant tunnelling structure (RTS) under external uniaxial pressure by photoluminescence studies. Compressive pressure parallel to the [110] direction, whose value is determined by Hooke's law, is imposed on the sample by a helix micrometer. With the increase of the applied external uniaxial compressive pressure, the blue shift and splitting of the luminescence peaks were observed, which have some influence on the I–V curve of RTS from the point of view of the energy gap, and the splitting became more apparent with applied pressure. Full width at half maximum broadening could also be observed.

Energy selective contacts for hot carrier solar cells

Double barrier resonant tunnelling structures consisting of silicon quantum dots (QDs) in silicon dioxide ( SiO 2 ) matrix have been studied for Energy Selective Contacts for Hot Carrier solar cell. A single layer of silicon QDs has been fabricated by high temperature annealing of SiO 2 / Si-rich oxide (SRO)/ SiO 2 layers deposited by RF magnetron sputtering. Compositional analysis of SRO films obtained with different sputtering target has been accurately measured with Rutherford backscattering spectroscopy. Size-controlled growth of Si QDs has been studied with photoluminescence measurements which demonstrate that QD sizes can be controlled with SRO layer thickness. In addition, resonant tunnelling behaviour of SiO 2 / Si QD/ SiO 2 structures has been investigated.

Spin-polarization in InAs/AlSb double barrier resonant tunneling structures: influence of barrier material and interface structure

We present a study on the atomistic simulation of the spin-polarized transmissions through InAs/AlSb double barrier resonant tunneling heterostructures. By making use of the atomistic sp3s* tight binding Hamiltonian including the intra-atomic spin-orbit interaction and the recursive Green’s function method, we obtain the significant anisotropic zero-magnetic-field spinsplitting of the resonant transmission peak in the absence of the external electric field, demonstrating the importance of the barrier material and the atomic scale detail of the hetero interfaces on the spin-splitting.

Doublet resonances of an electron in symmetric three-barrier resonant tunneling structures

The evolution and collapse of electron resonances and their spectral parameters in a symmetric three-barrier resonant tunneling structure (TBRTS) are studied theoretically. The resonance energy and width of the quasi-stationary states of an electron are analyzed. The quasi-stationary states are calculated by the transmission coefficient method, the method of the probability distribution function (the probability of finding an electron in a TBRTS), and the scattering cross section method.

Plane two-barrier resonance-tunneling structures: Resonance energies and resonance widths of quasi-stationary electron states

A theory of resonance energies and widths of quasi-stationary states is suggested; this theory is based on the distribution function of the probability density for the location of an electron in a two-barrier resonance-tunneling structure, and on the use of a transfer matrix and an S scattering matrix in the models of rectangular and δ-shaped potentials with various effective masses in the layers of the nanosystem. With an In0.53Ga0.47As/In0.52Al0.48As nanosystem as an example, the evolution of spectral parameters of an electron’s quasi-stationary states is analyzed in relation to geometric sizes of the resonance-tunneling structure; these states were calculated using three different methods. It is shown that, since the δ-barrier model overestimates the resonance width by several tens of times in comparison with a more realistic model of rectangular potentials, the former model can be only used for rough estimations.

Design and analysis of a new structure of InAs/GaAs QDIP for 8–12 μm infrared windows with low dark current

Based on the effective mass Schrödinger equation and eight-band k.p method, we study optical absorption in the 8–12 µm infrared window through the conduction subbands of self-assembled InAs/GaAs pyramidal shape quantum dots (QDs) using the finite difference method. Considering homogeneous and inhomogeneous broadening effects, the absorption spectra of QDs are calculated. Regarding the simulation results, we design a QD infrared photodetector (QDIP) with a double barrier resonant tunnelling (DBRT) at λ = 10 µm. We calculate the responsivity, detectivity and dark current for the device, considering the coverage factor of QDs. To enhance the performance of the presented DBRT especially at near room temperature, we propose a modified QDIP with asymmetric multiple barrier resonant tunnelling structure. With the modified structure, the dark current reduces to about half an order of magnitude compared with DBRT–QDIP, and detectivity increases to 1.4 × 109 cm Hz1/2/W at 200 K.

Evolution and collapse of quasistationary states of an electron in planar symmetric three-barrier resonance-tunneling structures

A theory of the evolution and collapse of pairs of resonances because of a change in the strength (thickness) of the inner barrier is developed in a model of effective masses and symmetric, square, potential barriers for an electron in a planar three-barrier structure. Analytical and numerical calculations of the spectral parameters (resonance energies and widths) are performed by the transmission coefficient and probability distribution function method using the transfer and S matrices. It is shown that the collapse of the resonance energies and widths of all quasistationary states in a symmetric three-barrier structure occurs for practically the same thicknesses of the inner barriers, somewhat greater than the total thickness of the outer barriers. It is established that with respect to the square-barrier model the δ model overestimates the resonance energies by 10% and the resonance widths by almost a factor of 2.

Manipulation of spin polarization by charge polarization in GaMnN ferromagnetic resonant tunneling diode

We have investigated the dependence of spin polarization on charge polarization at room temperature in GaMnN-based ferromagnetic resonant tunneling structures with different Mn doping positions. Our results show that compared to the nonpolarization case, the degree of spin polarization can be enhanced by two to four times and resonant current intensity increases about fourfold at a moderate polarized-charge concentration of 1012/cm2. In addition, the dipole right case in magnetic resonant diodes has stronger impact on spin tunneling than the opposite one. These results demonstrate that tailoring charge polarization is a feasible way to tune electron spin polarization in piezoelectric-type ferromagnetic heterostructures.

Spin-polarization and magnetoresistance in graphene-based resonant-tunnelling structures

Spin-dependent transport of relativistic electrons through graphene based double barrier (well) structures with ferromagnetic electrodes have been theoretically investigated. Electron transmission with different spin states is strongly influenced by the incident wave vector, the height (depth) of the barrier and the separation between them. When the angle of the incident electrons is varied from zero to ±π/2, spin polarization varies from zero to 100% with characteristic oscillations that indicate spin anisotropy. Due to Klein tunnelling, spin-polarization is always zero for normal incident electrons; high spin-polarization only occurs at large incident angles. Because the resonance features in the spin-dependent transmission result from resonant electron states in wells or hole states in barriers, the conductance can reach e2/h in this resonant-tunnelling structure.

High transparency of a two-photon scattering channel in triple-barrier structures

An analytical solution of the Schrodinger equation with open boundary conditions in all scattering channels has been found for asymmetric triple-barrier resonance-tunneling structures with thin high barriers. This solution describes resonance transitions between three quantum levels in a high rf electric field. It is found that, under certain conditions, most electrons incident on the upper resonance level can emit two photons and leave a structure through the lower level without intermediate interaction with phonons. The structure appears to be almost absolutely transparent in a wide range of the rf field amplitude. This behavior fundamentally distinguishes the multiphoton scattering process from previously considered single-photon scattering processes and the quantum efficiency of such transitions can be twice as high as the maximum quantum efficiency of the transitions between neighboring levels and can reach a value of 160% in the limiting case.