The Energy Pulse-Oriented Crystallization Phenomenon in Solids (Laser Annealing)

The nature of the phenomenon which was discovered is as follows: nanosecond pulsed laser action at ~10⁷W/cm² radiation power density on ion-implanted semiconductor wafers with an amorphous layer results in the removal of (recrystallization) damage and amorphization in ion-implanted silicon. The dominant physical mechanism at a pulsed laser-solid interaction was, in many experiments, found to be rapid heating. The rate of temperature increase is determined by the energy density, pulse duration, absorption coefficient, heat capacity, and the system's thermal diffusivity. A high heat-release rate facilitates the heating and melting of thin surface layers of metals and semiconductors at micro-, nano-, and even picosecond energy pulsed action. By rapidly heating amorphous layers, they melt at significantly lower temperatures than the crystal melting temperature. This results in the emergence of a deeply supercooled molten layer. The subsequent cooling rates are between 10⁸ and 10¹⁴°C/s. The system cooling that follows may lead to crystalline, polycrystalline, or amorphous structures, depending on the cooling rate. Mass crystallization induces the emergence of the self-sustained crystallization phenomenon. High cooling rates result in an increase in both the limiting solubility of the doping elements in semiconductors, and the distribution coefficient compared with equilibrium values. Another phenomenon was found in nanosecond pulsed action on heterosystems, which are crystalline matrices with coherently embedded nanocrystals (quantum dot heterostructures). The melting temperature for small nanocrystals was found to significantly exceed the melting temperature of bulk material.