A novel microscopic mechanism for hydrogen-enhanced oxygen diffusion in p-doped silicon is proposed. A path for joint diffusion of O and H is obtained from an ab-initio molecular dynamics "kick" simulation. The migration pathway consists of a two-step mechanism, with a maximum energy of 1.46 eV. This path represents a 0.54 eV reduction in the static barrier when compared with the diffusion of isolated O in Si, in excellent agreement with experiments.

Transition state theory (TST) is the most widely used formalism for theoretical calculations of diffusion coeffcients of defects in solids. In this work, we test its validity for the case of vacancy diffusion in silicon. The diffusion coefficient directly obtained from molecular-dynamics simulations with a classical (Stillinger-Weber) potential is compared with TST predictions. Our results confirm the validity of TST for this system.

Adopting a real-space tight-binding supercell approach, we investigate interface roughness effects in semiconductor heterostructures. AlAs/GaAs/AlAs (001) QWs of average width W are considered, in which one of the interfaces is planar and the other has a shape defined by periodic steps with amplitude A and wavelength lambda. The oscillator strength f of the fundamental transition in the well describes the optical nature of the heterostructures. By investigating the wavefunctions as a function of the interface parameter A, we conclude that the f behavior with A is an optical signature of the quantum well to quantum wire crossover in the heterostructures. Recently, photoluminescence experiments showed that hydrostatic pressure produces an increase in the optical eficiency of heterostructures in which the interfaces present a high degree of roughness. In order to investigate this optical behavior, we discuss hydrostatic pressure effects on rough-interface heterostructures.