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HL: Halbleiterphysik

HL 35: Hybride Systeme und neue Materialien

HL 35.4: Vortrag

Donnerstag, 14. März 2002, 12:45–13:00, H13

Crystallization kinetiks of Ge₄Sb₁Te₅ — •Daniel Wamwangi, Njoroge Walter, and Wuttig Matthias — 1 Physikalisches Institut 1A RWTH Aachen, Sommerfeld Str.14 D-52056 Aachen.

Ge₄Sb₁Te₅ is a promising candidate for rewritable optical data storage employing phase change recording, where the speed of crystallization limits the maximum the available data transfer rate. In this study the crystallization kinetics of sputtered Ge₄Sb₁Te₅ thin films are correlated to the structural and density changes through temperature dependent sheet resistance measurements in conjuction with structural investigations employing X-ray diffraction (XRD) and X-ray reflectometry (XRR). Annealing of the Ge₄Sb₁Te₅ films above the phase transition temperature shows a resistivity decrease from 200 Ωcm to 3.1· 10⁻³ Ωcm. The transition temperature is determined to about 180^∘C and varied with heating rate. The rapid resistivity change corresponds to the structural transformation from an amorphous as-deposited state to a crystalline rock salt structure (a = 0.5974 ± 0.0002 nm). The activation energy for crystallisation, E_a is determined to 3.48 ± 0.12 eV by Kissinger’s analysis. Density values of 5.59 ±0.02 g/cm³ and 6.14 ±0.02 g/cm³ have been determined by XRR for the amorphous and crystalline phase, respectively. This corresponds to a density increase of 9.3% and a contraction of 9.1% in film thickness upon annealing. The growth of oxide layer is also observed to commence in the amorphous phase at 105^∘C and saturates to 1.7 nm at 140^∘C.