D. Luis

TWO-DIMENSIONAL TIGHT-BINDING MODEL OF AC CONDUCTIVITY IN POROUS SILICON

A time-dependent tight-binding model has been developed to study the ac conductivity in porous silicon. Assuming that carriers are allowed to hop between isolated pairs of Si nanocrystals embedded in a SiO2 matrix, the tunneling times have been calculated according to different geometries. The geometrical structure of porous silicon has been modeled with simple percolationlike clusters. By using the tunneling times, the ac conductivity behavior in the high-frequency regime has been calculated in the pair approximation. The conductivity increases with the frequency according to a power law with an exponent lower than unity. It is found that there is a strong dependence of the ac conductivity on the thickness of the SiO2 interconnecting layer.

Dynamics of a two-dimensional electron-hole system in a coupled quantum well

In this work, we have numerically integrated in space and time the effective-mass Schrodinger equation for a two-dimensional electron-hole system in a coupled quantum well system. Considering a time-dependent Hartree potential and an external electric field, we derive the nonlinear dynamical evolution of the carrier wave function. It is found that charge dynamically trapped in both wells produces a reaction field that modifies the system resonant condition. At different electron-hole sheet densities we show the possibility of multiple resonant tunneling peaks in a bilayer system.

Possibility of multiple tunnelling current peaks in a coupled quantum well system

In this work, we have numerically integrated in space and time the effective-mass nonlinear Schrodinger equation for an electron wave packet in a bilayer electron system. Considering both Hartree and exchange-correlation potentials, we have calculated the tunnelling rates between the two quantum wells when an external bias is applied in the double quantum well system. Due to the nonlinear effective-mass equation, it is found that the charge dynamically trapped in both wells produces a reaction field which modifies the system resonant condition. At different electronic sheet densities, we have shown the possibility of having multiple resonant tunnelling peaks in a bilayer electron system.

Possibility of spin device in a triple quantum well system

We have numerically integrated in space and time the effective mass nonlinear Schrodinger equation for an electron wave packet in an InAs triple quantum well system. Considering the local spin-density approximation, we have calculated the tunneling dynamics in the triple quantum well system when an external bias is applied in the center quantum well. In such a device, the injected electronic current that is initially unpolarized could be divided into two spin-up and spin-down polarized currents at the same time and voltage obtaining a double efficiency.

Coulomb effects and carrier diffusion in semiconductor quantum wires

We have solved in space and time the effective-mass nonlinear Schrodinger equation for an electron-hole gas in a semiconductor quantum wire. If the carrier density is large enough, we have obtained the diffusion of coupled electron and hole densities considering a Coulomb interaction between both electron-hole gases. In this way, we have shown the possibility of having an inverse Mott transition in a quantum wire after an optical excitation of the sample.

Coulomb effects and sub-band tunneling in quantum wells

We have solved, in space and time, the effective-mass nonlinear Schrodinger equation for two electron gases in a semiconductor structure. Considering a Coulomb interaction between the electron densities of each sub-band, we have obtained two time-varying moments in the heterostructure with two different frequencies. If the carrier densities are large enough, we have obtained important nonlinear effects in the carrier dynamics. In this way, we have shown the possibility of having another kind of terahertz electromagnetic radiation emerging from a double quantum well device.

Coulomb effects and terahertz emission in semiconductor superlattices

We have solved the effective-mass nonlinear Schrodinger equation for an electron-hole gas in a semiconductor superlattice in space and time. Considering a Coulomb interaction between both electron-hole gases in a semiconductor superlattice we have obtained a time-varying dipole moment in the heterostructure. In this way, we have shown the possibility of another kind of terahertz electromagnetic radiation that emerges from a semiconductor superlattice after optical excitation of the sample.

Tunneling escape process from a spin-polarized two-dimensional electron system

In this work, we have numerically integrated in space and time the effective-mass nonlinear Schrodinger equation for an electron wave packet in a double barrier heterostructure. Considering both polarized and unpolarized magnetic phases, we have studied the tunneling escape process from the two-dimensional electron gas. Due to the nonlinear effective-mass equation, it is found that the charge trapped dynamically in the quantum well produces a reaction field, which modifies the tunneling escape process in the quantum well. At different electronic sheet densities, we have shown the possibility of having magnetic phase-dependent tunneling rates.

Time-dependent magnetotunnelling of electrons in strongly coupled double quantum wells

In this work, we have numerically integrated in space and time the effective-mass Schrodinger equation for an electron wave packet in a strongly coupled double quantum well system. Considering an electronic Hartree interaction and a high magnetic field parallel to the growth plane, we have obtained a dynamical evolution for the electronic wave function. In our double quantum well system, we clearly show the existence of resonant tunnelling oscillations as a function of the electron wave number value in the growth plane. It is also found that the tunnelling time values between both quantum wells are decreased if the magnetic field is increased.