Crystallization of isolated amorphous zones in semiconductors

Thermal annealing, irradiation with electrons (25-300 keV), and irradiation with photons (hν = 2.33-3.88 eV) have been used to stimulate the crystallization of isolated amorphous zones in Si, Ge, GaAs, GaP and InP. Transmission electron microscopy and computer image analysis were used to determine the crystallization processes. For all materials, thermally stimulated crystallization occurred only at temperatures above 373 K. The electron-stimulated crystallization rate is sensitive to the electron energy. Initially, the rate decreases with increasing energy until it reaches a minimum at about one half the threshold displacement energy and then it increases. It is insensitive to the irradiation temperature between 90 and 300 K and to the crystal orientation. The effective diameter of the amorphous zone initially shrinks linearly with increasing electron dose. For the laser-induced crystallization experiments the crystallization rate in Si, but not in Ge, was sensitive to the temperature, with a faster rate occurring at 300 K than at 90 K. The photon and electron stimulated crystallization results indicate that a non-displacive mechanism causes bond breakage at the amorphous-crystalline interface. The re-formation of these interfacial bonds is responsible for the amorphous-to-crystalline transition.