Solid-phase epitaxy. Effects of irradiation, dopant, and pressure

Abstract

A unified model of solid-phase epitaxial growth (SPEG), explaining enhancing effects of ion irradiation, dopants, and pressure, is presented. The crystallization occurs by the movement of atoms in the amorphous phase in the vicinity of the crystalline–amorphous (c–a) interface, assisted by a free energy decrease associated with the transformation from amorphous to crystalline phase. Irradiation and electrically active dopants can increase the self-diffusivity of the amorphous solid by generating point defects in the amorphous solid and thus enhance the crystallization. An expression for the velocity of epitaxial growth is derived. The temperature dependence of the velocity is obtained from the expression for the velocity. The low activation energy of ion-induced SPEG is due to recombination of point defects. The crystallographic orientation dependence of SPEG is explained by the difference in the number of atomic sites necessary for crystal growth in different orientations. At low temperatures and high irradiation dose rates, a large number of atoms in the lattice of the crystalline substrate gets displaced and the free energy of the crystalline solid can increase to such a value that amorphization may take place. It is shown that the dose rate at which the c–a interface remains stationary increases with temperature, following an Arrhenius dependence. If a hydrostatic pressure is applied during SPEG. a tensile stress is developed in the amorphous layer, because the bulk modulus of the amorphous phase is smaller than that of the crystalline phase. This tensile stress increases the self-diffusivity in the amorphous layer and thereby enhances SPEG.