SHORT-PULSE LASER-INDUCED CRYSTALLIZATION OF INTRINSIC AND HYDROGENATED AMORPHOUS-GERMANIUM THIN-FILMS

We report on the laser crystallization of intrinsic (a-Ge) and hydroge nated (a-Ge:H) amorphous germanium thin films using short, i.e., ns ra nge, laser pulses. The influence of hydrogen on the phase transitions was investigated by monitoring the reflectance of the sample during la ser irradiation. We determined the thresholds for melting (36 mJ/cm(2) ) and for surface damage (66 mJ/cm(2)) of the a-Ge film. In a-Ge:H, hy drogen effuses on a short time scale (10 ns) upon laser irradiation. T he effusion leads to the formation of a lifted-off (100 nm thick) crys talline Ge membrane, leaving behind a rough and incompletely crystalli zed surface. In a-Ge, on the other hand, no surface disruption is obse rved. The Raman spectra of hydrogenated samples are dominated by stres s effects, while those corresponding to non-hydrogenated samples are d ominated by crystallite size distribution effects. We also conclude th at laser-induced annealing, carried out by applying several pulses wit h increasing intensity, can be used as a tool for the crystallization of a-Ge:H samples without hydrogen-induced surface damage. (C) 1997 Am erican Institute of Physics.