Laser-induced crystallization phenomena in GeTe-based alloys. I. Characterization of nucleation and growth

Abstract

The laser-induced crystallization behavior of GeTe-based amorphous alloy thin films has been quantitatively studied by local reflection measurements with a focused 780 nm laser. The use of multiple laser pulse sequences enables the nucleation rate and crystal-growth speed to be separately deduced, allowing the compositional variation of both these processes to be followed. This not only gives detailed information on the crystallization mechanism, but also allows the fine tuning of phase change alloy compositions for use in erasable optical recording. The differences between the as-deposited and melt-quenched amorphous phases are also discussed. In particular, it is shown that the crystallization speed of the as-deposited layer can differ by over an order of magnitude from that of the melt-quenched amorphous layer. The as-deposited state can, however, be transformed into a modified amorphous state equivalent to that obtained by melt quenching a previously crystalline layer. This allows the determination of the optical constants and crystallization speeds of the amorphous state written during optical recording.

Phase change in Ge2Sb2Te5 films investigated by coherent phonon spectroscopy

“…They offer suitable crystallization and melting temperatures for laserinduced phase changes and rapid transition times in the nanosecond range. [1][2][3] Previous investigations on the structural and optical properties of the Ge-Sb-Te compound system have been performed by electron diffraction, 4 x ray, 5 and optical spectroscopy. 6,7 Over a wide compositional range, amorphous Ge-Sb-Te films crystallize in a ''metastable'' cubic NaCl-type lattice at temperatures between 120 and 150°C.…”

Особенности распределения электронной плотности в теллуриде сурьмы Sb-=SUB=-2-=/SUB=-Te-=SUB=-3-=/SUB=-

“…Востребованность PCM в практически важных при-ложениях для хранения данных обусловлена сочетанием их уникальных свойств: заметным различием оптических характеристик (коэффициентов отражения и пропуска-ния лазерного света в широком спектральном диапа-зоне) в аморфном и кристаллическом состоянии [6], малыми временами и низким энергетическим порогом кристаллизации и аморфизации под действием лазерного излучения [7] или импульса электрического тока [8], резким увеличением электросопротивления при пере-ходе из кристаллического в аморфное состояние [8,9], стабильностью фазового состояния в области темпе-ратур от комнатной до 150−200…”

Phase-Change Media for High-Density Optical Recording

“…In this way, the complete erasure time (CET), i.e. the minimum time to erase the amorphous mark, was determined [7]. The experiments were performed on actual discs, consisting of 4-layer recording stacks sputter-deposited onto a polycarbonate substrate.…”

“…The crystallization speed of the eutectic GeSbTe alloys was studied first by using a statictester setup [7]. In static-tester experiments, amorphous marks of different size were written by varying the write power at a fixed write-pulse length.…”