43 research outputs found
Description of bulk inversion asymmetry in the effective-bond-orbital model
We have extended the effective-bond-orbital model (EBOM) method [Y. C. Chang, Phys. Rev. B 37, 8215 (1988)] to include the effects of the bulk inversion asymmetry (BIA) present in zinc blendes. This is accomplished without adding to the number of basis states or extending the range of interaction. We have also investigated a variant form of the EBOM proposed in the original formulation that offers improved zone-center behavior, but may also generate spurious solutions in heterostructure calculations due to poor description of bulk zone-boundary band structure. We offer suggestions for avoiding this problem so that this variant form of EBOM may be used safely. In general, we find that the addition of BIA effects in EBOM results in improved descriptions of zone-center band structure, but also in a loss of accuracy far from the Brillouin-zone center. We illustrate the use of the BIA extension with band-structure calculations for bulk GaSb. We show that the spin splitting predicted by the extended EBOM method for an AlSb/GaSb superlattice is in good agreement with k·p calculations that include BIA effects
Numerical spurious solutions in the effective mass approximation
We have characterized a class of spurious solutions that appears when using the finite difference method to solve the effective mass approximation equations. We find that the behavior of these solutions as predicted by our model shows excellent agreement with numerical results. Using this interpretation we find a set of analytical expressions for conditions that the Luttinger parameters must satisfy to avoid spurious solutions. Finally, we use these conditions to check commonly used sets of parameters for their potential for generating this class of spurious solutions
Tunnel switch diode based on AlSb/GaSb heterojunctions
We report on tunnel switch diodes based on AlSb barriers and GaSb p–n junctions grown by molecular beam epitaxy. These were the devices with thyristor like switching in the GaSb/AlSb system. The characteristic "S" shaped current–voltage curve was found to occur for structures with AlSb barriers less than 300 Å thick. The switching voltage and current density exhibited less sensitivity to barrier and epilayer thickness than was predicted by the punch-through model. The results were correlated with drift diffusion simulations which have been modified to account for the presence of a tunneling contact
Suppression of the D'yakonov-Perel' spin relaxation mechanism for all spin components in [111] zincblende quantum wells
We apply the D'yakonov-Perel' (DP) formalism to [111]-grown zincblende
quantum wells (QWs) to compute the spin lifetimes of electrons in the
two-dimensional electron gas. We account for both bulk and structural inversion
asymmetry (Rashba) effects. We see that, under certain conditions, the spin
splitting vanishes to first order in k, which effectively suppresses the DP
spin relaxation mechanism for all spin components. We predict extended spin
lifetimes as a result, giving rise to the possibility of enhanced spin storage.
We also study [110]-grown QWs, where the effect of structural inversion
asymmetry is to augment the spin relaxation rate of the component perpendicular
to the well. We derive analytical expressions for the spin lifetime tensor and
its proper axes, and see that they are dependent on the relative magnitude of
the BIA- and SIA-induced splittings.Comment: v1: 5 pages, 2 figures, submitted to PRL v2: added 1 figure and
supporting content, PRB forma
A simple drain current model for Schottky-barrier carbon nanotube field effect transistors
We report on a new computational model to efficiently simulate carbon
nanotubebased field effect transistors (CNT-FET). In the model, a central
region is formed by a semiconducting nanotube that acts as the conducting
channel, surrounded by a thin oxide layer and a metal gate electrode. At both
ends of the semiconducting channel, two semi-infinite metallic reservoirs act
as source and drain contacts. The current-voltage characteristics are computed
using the Landauer formalism, including the effect of the Schottky barrier
physics. The main operational regimes of the CNT-FET are described, including
thermionic and tunnel current components, capturing ambipolar conduction,
multichannel ballistic transport and electrostatics dominated by the nanotube
capacitance. The calculations are successfully compared to results given by
more sophisticated methods based on non-equilibrium Green's function formalism
(NEGF).Comment: 22 pages, 9 figure