Nanosecond laser-induced phase transitions in pulsed laser deposition-deposited GeTe films

Abstract

Phase transformations between amorphous and crystalline states induced by irradiation of pulsed laser deposition grown GeTe thin films with nanosecond laser pulses at 248nm and pulse duration of 20ns are studied. Structural and optical properties of the Ge-Te phase-change films were studied by X-ray diffraction and optical reflectivity measurements as a function of the number of laser pulses between 0 and 30 pulses and of the laser fluence up to 195 mJ/cm2. A reversible phase transition by using pulse numbers ≥5 at a fluence above the threshold fluence between 11 and 14 mJ/cm2 for crystallization and single pulses at a fluence between 162 and 182 mJ/cm2 for amorphization could be proved. For laser fluences from 36 up to 130 mJ/cm2, a high optical contrast of 14.7% between the amorphous and crystalline state is measured. A simple model is used that allows the discussion on the distribution of temperature in dependency on the laser fluence.