Pulsed laser-induced amorphization of silicon films

Abstract

The reversible transition from crystalline to amorphous silicon was observed on films deposited on quartz substrates through laser-induced melting using a 30-ns pulsed XeCl excimer laser. A 20-nm-thick silicon film was completely melted and then amorphized. The melt duration exceeded 70 ns when the film was amorphized. The transition from liquid to the amorphous state would occur homogeneously throughout the film because the temperature gradient in molten silicon could be reduced to 1.0×105 K/cm (0.2 K/20 nm) at 70 ns after initiation of melt. The laser-amorphized film had a large mid-gap density of states of 5.3×1019 cm−3 eV−1. The density of states was remarkably reduced using a hydrogen plasma treatment at 250 °C for only 1 min. Thin-film transistors fabricated in a laser-amorphized film showed good characteristics with a carrier mobility of 0.6 cm2/V s after hydrogenation.