Origin of laser-assisted and doping-assisted phenomena in semiconductors: II. Surface reactions

Abstract

(For pt.1, see Phys. Status Solidi, vol.149, p.465 (1988)). Electronic and/or optical excitation at surfaces is assumed to modify the cohesive properties of localised sites. This leads to change of the activation energy and entropy for surface-assisted mechanisms (adsorption, desorption and reactions). These are introduced into the models leading to the Langmuir and BET isotherms. It is also shown how the Eley-Rideal and Langmuir-Hinshelwood mechanisms are modified upon electronic excitation. In order to understand how electronic excitation may modify reaction rates, a reaction is considered in which a normally non-volatile intermediate product becomes volatile upon electronic excitation. This is discussed in the case of doping-assisted reaction and laser-assisted reaction. In this last case, by taking into account the effects of laser irradiation on localised states and on the temperature of the irradiated zone, one may describe situations where either rapid saturation or slow increase, or a sharp threshold for reaction takes place.