Crystallization of Ge2Sb2Te5 thin films by nano- and femtosecond single laser pulse irradiation.
The amorphous to crystalline phase transformation of Ge2Sb2Te5 (GST) films by UV nanosecond (ns) and femtosecond (fs) single laser pulse irradiation at the same wavelength is compared. Detailed structural information about the phase transformation is collected by x-ray diffraction and high resolution transmission electron microscopy (TEM). The threshold fluences to induce crystallization are determined for both pulse lengths. A large difference between ns and fs pulse irradiation was found regarding the grain size distribution and morphology of the crystallized films. For fs single pulse irradiated GST thin films, columnar grains with a diameter of 20 to 60 nm were obtained as evidenced by cross-sectional TEM analysis. The local atomic arrangement was investigated by high-resolution Cs-corrected scanning TEM. Neither tetrahedral nor off-octahedral positions of Ge-atoms could be observed in the largely defect-free grains. A high optical reflectivity contrast (~25%) between amorphous and completely crystallized GST films was achieved by fs laser irradiation induced at fluences between 13 and 16 mJ/cm(2) and by ns laser irradiation induced at fluences between 67 and 130 mJ/cm(2). Finally, the fluence dependent increase of the reflectivity is discussed in terms of each photon involved into the crystallization process for ns and fs pulses, respectively.
Leibniz Institute of Surface Modification, Permoserstr. 15, D-04318 Leipzig, Germany.
Xinxing
X
Sun
Leibniz Institute of Surface Modification, Permoserstr. 15, D-04318 Leipzig, Germany.
Martin
M
Ehrhardt
Leibniz Institute of Surface Modification, Permoserstr. 15, D-04318 Leipzig, Germany.
Andriy
A
Lotnyk
Leibniz Institute of Surface Modification, Permoserstr. 15, D-04318 Leipzig, Germany.
Pierre
P
Lorenz
Leibniz Institute of Surface Modification, Permoserstr. 15, D-04318 Leipzig, Germany.
Erik
E
Thelander
Leibniz Institute of Surface Modification, Permoserstr. 15, D-04318 Leipzig, Germany.
Jürgen W
JW
Gerlach
MTA-SZTE Research Group on Photoacoustic Spectroscopy, University of Szeged, Dóm tér 9, H-6720 Szeged, Hungary.
Tomi
T
Smausz
Leibniz Institute of Surface Modification, Permoserstr. 15, D-04318 Leipzig, Germany.
Ulrich
U
Decker
Leibniz Institute of Surface Modification, Permoserstr. 15, D-04318 Leipzig, Germany.|Institute for Experimental Physics II, Leipzig University, Linnéstr. 5, D-04103 Leipzig, Germany.
Bernd
B
Rauschenbach