Substrate and doping effects upon laser-induced epitaxy of amorphous silicon

Abstract

UHV‐deposited amorphous silicon was recrystallized on (100) single‐crystal substrates using pulsed Nd : YAG laser irradiation. Prior to deposition, substrates were prepared with either atomically clean surfaces, residual argon ion sputter damage, or from one to three monolayers of residual oxide. Epitaxial regrowth of bulk crystalline quality occurred regardless of substrate preparation. Annealing energy densities were significantly higher, however, for substrates retaining residual impurities. Certain layers were doped with Ga. At moderate doping levels recrystallization behavior was unaffected. At a 2% doping level, the annealing energy threshold dropped by one‐half and Ga atoms were displaced toward the epitaxial surface. It is shown that the decrease in energy threshold is due to an impurity‐induced increase in light absorption within the amorphous layer. Layers were crystallized with substitutional Ga concentrations of up to 10 times the equilibrium solid solubility limit.