Berlin 2005 – wissenschaftliches Programm

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VA: Vakuumphysik und Vakuumtechnik

VA 3: Vakuumverfahren und Komponenten 1

VA 3.2: Vortrag

Montag, 7. März 2005, 14:30–14:50, TU E20

Shutter-transients during solid-source epitaxy — •Christian Heyn and Sabine Cunis — Institut für Angewandte Physik und Zentrum für Mikrostrukturforschung, Jngiusstraße 11, D-20355 Hamburg, Germany

Effusion cells are commonly used in solid-source molecular beam epitaxy for evaporation of the source materials. A prominent inaccuracy during effusion cell operation are strong flux transients after shutter opening. We have studied the temperature and time dependent beam fluxes of effusion cells filled with the group III elements Indium, Aluminium and Gallium. A flux reduction due to the shutter-transient up to 35% with time constants ranging from 25 to 100 s is observed. A simple model of the shutter transient behavior is proposed that well reproduces major features of the experiments. As a key point, we do not model the effusion cell simply as a Knudsen cell, but assume instead more realistic Langmuir evaporation. Two applications are presented. First the calibration of beam fluxes under consideration of the shutter-transient, and, second, a technique for the compensation of the shutter-transient by an optimized temperature control.