Nonlinear stochastic discrete drift-diffusion theory of charge fluctuations and domain relocation times in semiconductor superlattices

A stochastic discrete drift-diffusion model is proposed to account for the effects of shot noise in weakly coupled, highly doped semiconductor superlattices. Their current-voltage characteristics consist of a number stable multistable branches corresponding to electric field profiles displaying two domains separated by a domain wall. If the initial state corresponds to a voltage on the middle of a stable branch and a sudden voltage is switched so that the final voltage corresponds to the next branch, the domains relocate after a certain delay time. Shot noise causes the distribution of delay times to change from a Gaussian to a first passage time distribution as the final voltage approaches that of the end of the first current branch. These results agree qualitatively with experiments by Rogozia {\it et al} (Phys. Rev. B {\bf 64}, 041308(R) (2001)).Comment: 9 pages, 12 figures, 2 column forma

Lifetime of metastable states in resonant tunneling structures

We investigate the transport of electrons through a double-barrier resonant-tunneling structure in the regime where the current-voltage characteristics exhibit bistability. In this regime one of the states is metastable, and the system eventually switches from it to the stable state. We show that the mean switching time grows exponentially as the voltage across the device is tuned from the its boundary value into the bistable region. In samples of small area we find that the logarithm of the lifetime is proportional to the voltage (measured from its boundary value) to the 3/2 power, while in larger samples the logarithm of the lifetime is linearly proportional to the voltage.Comment: REVTeX 4, 5 pages, 3 EPS-figure

Transient Experiments on CO₂ Formation by the CO Oxidation Reaction over Oxygen-Rich Ru(0001) Surfaces

Reactive scattering of CO molecules at oxygen-rich Ru(0001) surfaces with concentrations equivalent up to 16 monolayers and sample temperatures between 300 and 700 K led to the identification of two distinct reaction channels in the transient CO2 rate. The first reaction channel is related to the recombination of CO molecules with oxygen atoms already located on the surface. The second reaction channel, which can be observed at sample temperatures above about 400 K, is controlled by the diffusion of oxygen atoms from the near-surface region toward the surface