Study On Microstructure And Optical Properties Of Ge₂Sb₂Te₅ Phase-change Films

Optical data storage techniques are playing a more and more important role in modern information society, but the traditional optical disc storage techniques is facing the challenge not only from the rapid development of other data storage techniques, but also from the demands of new optical disk storage products with higher storage density and capacity. Optical storage is developing towards high density, large capacity, high data transfer rate and multifunctional usage. Among the others, phase-change materials and technology have been art racting more and more interest because of their successful application in rewritable optical storage.In this study, Ge₂Sb₂Te₅ thin films have been deposited on n-Si (100) and quartz substrates by radio frequency magnetron sputtering. The influence of substrate temperture and sputtering pressure is emphasized. The morphological and structural chacterizations have been carried out using atomic force microsiscopy, transmission electron microscopy, x-ray diffraction. The major points of this thesis are summarized as follows:1. Using a radio-frequency magnetron sputtering method, Ge₂Sb₂Te₅ films were grown on quartz substrates at room temperature. X-ray diffraction analysis revealed the as-deposited films to be amorphous. The films have a face-center-cubic (fcc) structure with the grain size of 17 nm and hexagonal (hex) structure with the grain size of 40 nm after annealed at 170°C and 250°C in a vacuum chamber, respectively. The thermodynamics behavior of the phase transition of the films was studied in the temperature ranging from room temperature to 450°C. It was found the activation energy of phase transition to be 2.03±0.15eV from amorphous to fcc phase and 1.58±0.24eV from fcc phase to hex phase. The reflection contrast increases from 15 to 30% for fcc films and from 30 to 40% for hex films with increasing the wavelength from 400 to 1000 nm. Under the irradiation of a 5 mW pulsed laser at a wavelength of 650 nm, the influence of pulse width on the phase transition was studied for the laser pulse durations of 40, 50, 75,100, 400, and 1000 ns.2. Ge₂Sb₂Te₅ thin films have been deposited on glass substrates and Si( 100) substrates with a native oxide layer. The structures and morphologies of the films have been determined by using X-ray diffraction, scanning electron microscopy, atomic force microscopy and ultraviolet spectrometer. The films were deposited at the substrates temperatures of room...