Relaxation of Electron Spin during High-Field Transport in GaAs Bulk

A semiclassical Monte Carlo approach is adopted to study the multivalley spin depolarization of drifting electrons in a doped n-type GaAs bulk semiconductor, in a wide range of lattice temperature ($40<T_L<300$ K) and doping density ($10^{13}<n<10^{16}$cm$^{-3}$). The decay of the initial non-equilibrium spin polarization of the conduction electrons is investigated as a function of the amplitude of the driving static electric field, ranging between 0.1 and 6 kV/cm, by considering the spin dynamics of electrons in both the $\Gamma$ and the upper valleys of the semiconductor. Doping density considerably affects spin relaxation at low temperature and weak intensity of the driving electric field. At high values of the electric field, the strong spin-orbit coupling of electrons in the $L$-valleys significantly reduces the average spin polarization lifetime, but, unexpectedly, for field amplitudes greater than 2.5 kV/cm, the spin lifetime increases with the lattice temperature. Our numerical findings are validated by a good agreement with the available experimental results and with calculations recently obtained by a different theoretical approach.Comment: 14 pages, 6 figure

Self-consistent Monte Carlo particle modelling of small semiconductor elements.

A self-consistent Monte Carlo particle model aimed at a profound physical understanding of small semiconductor components of arbitrary geometries is presented. The simulation technique consists briefly of following the transport histories of individual charge carries in detail. After a discussion of the stochastic distribution of the time of free flight, the scattering mechanisms and the scattering angles of the particles, a brief review of the relevant semiconductor is given. As an example to illustrate the salient points of the technique, the results of simulating a GaAs field-effect transistor will be discussed. The presentation of the transistor characteristics is used to establish a link between theoretical physics and the view of the electrical engineer. A short discussion of statistical phenomena such as noise, negative differential resistivity and substrate currents has also been included

Electromagnetic radiation from hot carriers in FET-devices.

We report on the emission of light from Si MOS and GaAs MES devices. Processes involving band-to-band transitions and a Bremsstrahlung-continuum below the bandgap are shown to exist. Spatially nonuniform emission from the MESFETs is observed. The GaAs results are compared with Monte Carlo simulations

Time-resolved photocurrent response of metal-semiconductor-metal photodetectors to double-pulse excitation.

The photocurrent response of a GaAs metal-semiconductor-metal (SMS) photodetector was measured after excitation with two femtosecond pulses having a variable delay Deltat of 0 ps equal or smaller than Deltat equal or smaller than 100 ps. At low excitation densities the influence of the first pulse on the pulse shape of the second is negligible for Deltat equal or bigger than 20 ps. This corresponds to a resolvable pulse train of 50 GHz repetition rate for the detectors used in our experiments. The influence of space charge effects at higher excitation density and/or lower bias could be shown

Limitations of the impulse response of GaAs metal-semiconductor metal photodetectors.

Photoconductive and electro-optic sampling of the photocurrent of GaAs metal-semiconductor-metal- photodiodes reveal the influence of field screening and optical phonon scattering on the frequency bandwidth of these detectors. The experimental results agree with theoretical predictions of a self- consistent two-dimensional Monte Carlo calculation

Characterization of picosecond GaAs metal-semiconductor-metal photodetectors.

Interdigitated GaAs metal-semiconductor-metal Schottky photodiodes have been studied experimentally and theoretically. The time evolution of the response current has been measured by means of photoconductive and electrooptic sampling with a time resolution of 0.8 and 0.3 ps, respectively. The response current to a 70 fs laser pulse reaches maximum within 2-5 ps, then shows a fast decay of about 10 ps followed by a slower one. Self-consistent, two-dimensional Monte Carlo particle simulation predicts that the former is due to electrons, the latter to holes. With a sufficiently strong electric field the two species of carriers get separated. With increased light intensity a screened plasma forms that vanishes only through recombination which takes of the order of nanoseconds