Catálogo de publicaciones - libros

We employ a three-dimensional (3D) particle-in-cell method coupling with finite-difference time domain scheme to simulate the electron emission in surface conduction electron-emitter displays (SEDs). This computational technique includes the space charge effects automatically. We thus explore the conducting mechanism, the emission efficiency, and the current density distribution on the anode plate with one field emission emitter.

We present a microscopic model of the photocurrent in quantum well solar cells (QWSC), based on the non-equilibrium Green’s function formalism (NEGF) for a multiband tight-binding Hamiltonian. The quantum kinetic equations are self-consistently coupled to Poisson’s equation. Relaxation and broadening mechanisms are considered by the inclusion of acoustic and optical electron-phonon interaction in a self-consistent Born approximation of the scattering self energies. Results are shown for the density of states, spectral response, current spectrum and IV-characteristics of single quantum well -structures.

A Monte Carlo method has been used to investigate the dynamics of a terahertz quantum cascade laser. The simulator follows the evolution of both electrons and photons and makes use of a special weighting procedure in order to cope with the huge variations in the number of photons. The laser turn-on time is found to be much longer than the time needed to establish the electron population inversion. Moreover, it presents an important statistical dispersion which reflects the “rare events” statistics of photon emissions during the initial stage. The response to a modulation of either optical losses or injected current has been investigated and the laser turn-on delay appears as the main factor that limits the response at high frequency.

We present the CAD multiscale device simulation software. The scope of the project is a full description of charge transport and optoelectronic properties of devices with embedded active regions of nanometer-scale. We show simulations of a GaN LED that requires modeling of strain, transport of electrons, holes and excitons and device heating.

We clarify the mechanism of single electron hopping and demonstrate single electron ocsillation via Si-dot, using a high-presice general-puprpuse device-simulator.

We simulate the spin transport properties in Schottky Barrier FET by ensemble Monte Carlo Method. Based on the three subbands approximations of 2DEG a more accurate model to calculate the spin precession frequency is adopted. With intra-subband and inter-subband scatterings fully considered, the three subbands approximation is compared with the single band approximation. We also examine the influence of the external electric field on the dephasing of the injected spin polarization. The simulation results can provide some guidance for the future design of SpinFET.

We present preliminary results of a discontinuous Galerkin scheme applied to deterministic computations of the transients for the Boltzmann-Poisson system describing electron transport in semiconductor devices. The collisional term models optical-phonon interactions which become dominant under strong energetic conditions corresponding to nanoscale active regions under applied bias. The proposed numerical technique, that is a finite element method which uses discontinuous piecewise polynomials as basis functions, is applied for investigating the carrier transport in bulk silicon and in a silicon − − diode. Additionally, the obtained results are compared to those of a high order WENO scheme solver.

Formation of shock waves in two-dimensional electron channels by electrical signals is studied using analytical and numerical models based on hydrodynamic electron transport equations coupled with two-dimensional Poisson equation.

Two-dimensional transient simulations of AlGaN/GaN HEMTs are performed in which a deep donor and a deep acceptor are considered in a semi-insulating buffer layer. It is shown that lag phenomena and current slump could be reproduced. Particularly, it is shown that gate lag is correlated with relatively high source access resistance of AlGaN/GaN HEMTs, and that drain lag could be a major cause of current slump. The current slump is more pronounced when the deep-acceptor density in the buffer layer is higher and when an off-state drain voltage is higher, because trapping effects become more significant. It is concluded that an acceptor density in the buffer layer should be made low to minimize current slump, although current cutoff behavior may be degraded when the gate length is short.

An electrothermal Monte Carlo method is applied to study various GaN heterostructures designed to improve electron confinement in the channel of the structures. It is shown that the use of a p-type GaN buffer and the inclusion of a thin InGaN back-barrier below the channel in AlGaN/GaN HFETs improve the device pinch-off characteristics, but increase the influence of self-heating. Results show that the use of an AlGaN exclusion layer at the AlGaN/GaN interface increases both the device currents and temperatures.