É́tude sur la cinétique des défauts structuraux dans le silicium amorphe
This thesis presents the results of both computational and experimental studies on the role of structural defects in amorphous silicon. The computational work was done using a novel kinetic Monte-Carlo method to simulate the time evolution of defective models of amorphous silicon over timescales reaching one second at room temperature. These simulations show that the vacancy in amorphous silicon is unstable and does not diffuse without being annihilated. We also show that the annealing behavior of an ion-damaged model of amorphous silicon can be divided in two phases: the initial one being dom- inated exclusively by the diffusion and rapid creation/annihilation of bond defects, the other one with bond defect creation/annihilation being progressively replaced by bond exchanges from perfectly coordinated atoms. Defects also have an effect on the viscosity amorphous silicon. To explore this further we mesure the radiation-enhanced viscosity of pure and hydrogenated amorphous silicon under the effect an ion-beam. We show the change in viscosity is different, the hydrogenated samples having a constant density while the pure amorphous silicon samples having a viscosity that increases linearly with ion fluence. At low fluence, the viscosity of hydrogenated amorphous silicon is higher than the viscosity of pure amorphous silicon. The presence of hydrogen also reduces the amplitude of the logarithmic stress change observed during annealing at room tempera- ture.
relaxation structurelle silicon amorphous viscosity structural relaxation vacancy