Selective ultrashort laser annealing of amorphous Ge/Si multilayer stacks

¹ HiLASE Centre, Institute of Physics of the Czech Academy of Sciences, 25241 Dolní Břežany, Czech Republic
² Rzhanov Institute of Semiconductor Physics SB RAS, 630090 Novosibirsk, Russia
³ Novosibirsk State University, 630090 Novosibirsk, Russia
⁴ Czech Technical University, Faculty of Nuclear Sciences and Physical Engineering, 11519 Prague, Czech Republic
⁵ Coherent LaserSystems GmbH & Co. KG, 37079 Göttingen, Germany
⁶ Valiev Institute of Physics and Technology, Yaroslavl Branch, Russian Academy of Sciences, 150007 Yaroslavl, Russia

^* Corresponding author: bulgakova@fzu.cz

Published online: 24 October 2022

Abstract

We report on single-short laser crystallization of Ge/Si multilayer stacks consisting of alternating amorphous nanosized films of silicon and germanium using near- and mid-infrared femtosecond and picosecond laser pulses. The phase composition of the irradiated stacks was investigated by the Raman scattering technique. Several non-ablative regimes of crystallization were found, from partial crystallization of germanium without intermixing the Ge/Si layers to complete intermixing of the layers with formation of GexSi1-x solid alloys. The roles of one- and two-photon absorption, thermal and non-thermal (ultrafast) melting processes, and laser-induced stresses in selective pico- and femtosecond laser annealing are analysed based on theoretical estimations and comparison with experimental data. It is concluded that, due to a mismatch of the thermal expansion coefficients between the adjacent stack layers, efficient explosive solid-phase crystallization of the Ge layers is possible at relatively low temperatures, well below the melting point. The possibility of ultrafast non-thermal phase transition in germanium in the studied regimes is also discussed.