Photo-enhanced crystallization by laser irradiation and thermal annealing in amorphous GeSe 2

Abstract

The laser irradiated crystallization process in amorphous GeSe 2 was studied by Raman scattering to discriminate between thermal and photo-induced contributions. Amorphous GeSe 2 crystallizes into a low-temperature (LT) form, LT-GeSe 2, and a high-temperature (HT) form, HT-GeSe 2. An amorphous sample was annealed at various temperatures and times in an electric furnace with and without laser irradiation. The laser power was adjusted to about 20 mW having a 0.4 mm spot size to determine the photo-induced effect. The difference between the thermal and laser irradiated crystallization process was discussed by considering the activation energy of crystallization. The activation energy due to laser irradiation above the band-gap energy was found to be smaller than that for the pure thermal crystallization process. We present a model for the photo-enhanced effect in which the lone-pair electrons of Se atoms are excited by the photons and the bond switching or atomic rearrangement occurs when the electrons relax through an electron–phonon interaction.