OPTICAL CHARACTERIZATION OF LASER-INDUCED CRYSTALLIZED SILICON FILMS

Optical absorption coefficient spectra of thin silicon films were prec isely investigated using a simple reflectance system with total reflec tance mirrors placed on the rear side of samples in order to cancel an interference effect in a range between 1.1 eV and 3 eV. The absorptio n coefficient decreased according to crystallization as the laser ener gy increased and it got similar to that of single crystalline silicon in the range of 1.7 eV similar to 3 eV. However, the absorption coeffi cient was higher than 10(2) cm(-1) in the photon energy lower than 1.3 eV. This probably results from band tail states caused by defect stat es localized at grain boundaries in the crystallized films. 2.5%-phosp horus doped laser crystallized silicon films had a high optical absorp tion coefficient ( > 10(4) cm(-1)) in the low photon energy range (1.1 eV similar to 1.7 eV) caused by free carriers produced from the dopan t atoms activated in the silicon films. The experimental results gave the carrier density of 1.3 x 10(21) cm(3) and the carrier mobility of 20 cm(2)/Vs.