Optical evidence for a self-propagating molten buried layer in germanium films upon nanosecond laser irradiation

Journal Article · Sun May 15 04:00:00 EDT 2005 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.1900932· OSTI ID:20709647

Vega, F; Chaoui, N; Solis, J; Armengol, J; Afonso, C N ^[1]

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1. Departament d'Optica i Optometria, Universitat Politecnica de Catalunya, C/Violinista Vellsola 37, 08222 Terrassa (Spain)

This work describes the phase transitions occurring at the film-substrate interface of amorphous germanium films upon nanosecond laser-pulse-induced melting of the surface. Films with thickness ranging from 50 to 130 nm deposited on glass substrates were studied. Real-time reflectivity measurements with subnanosecond time resolution performed both at the air-film and film-substrate interfaces were used to obtain both surface and in-depth information of the process. In the thicker films ({>=}80 nm), the enthalpy released upon solidification of a shallow molten surface layer induces a thin buried liquid layer that self-propagates in-depth towards the film-substrate interface. This buried liquid layer propagates with a threshold velocity of 16{+-}1 m/s and causes, eventually, melting at the film-substrate interface. In the thinnest film (50 nm) there is no evidence of the formation of the buried layer. The presence of the self-propagating buried layer for films thicker than 80 nm at low and intermediate laser fluences is discussed in terms of the thermal gradient in the primary melt front and the heat released upon solidification.

• OSTI ID: 20709647
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 10 Vol. 97; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ENTHALPY
GERMANIUM
GLASS
INTERFACES
LASER RADIATION
LASERS
LAYERS
MELTING
PULSES
REFLECTIVITY
SEMICONDUCTOR MATERIALS
SOLIDIFICATION
SUBSTRATES
TEMPERATURE GRADIENTS
THIN FILMS
TIME RESOLUTION