Local Order and Crystallization of Laser Quenched and Ion Implanted Amorphous Ge 1-x Te x Thin Films
- PDF / 533,466 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 15 Downloads / 167 Views
1251-H02-08
Local order and crystallization of laser quenched and ion implanted amorphous Ge1-xTex thin films
E. Carria1,2, R. De Bastiani2, S. Gibilisco1,2, A. Mio1, M. Miritello1,2 , A. R. Pennisi1,2, C. Bongiorno3, M. G. Grimaldi1,2, E. Rimini1,3 1
Dipartimento di Fisica ed Astronomia, Università di Catania, 64 via S. Sofia, I-95123 Catania, Italy 2 MATIS-IMM-CNR, 64 via S. Sofia, I-95123 Catania, Italy 3 IMM-CNR, 50 Stradale Primosole, I-95121 Catania, Italy
ABSTRACT Amorphous films of Ge1-xTex (x=0.37, 0.51, 0.64) prepared by sputtering, by melt quenching or by ion irradiation were annealed up to 450°C. Different phase stability, i.e. crystallization temperature, was observed varying the amorphous status in stoichiometric and Terich alloys while no variation was obtained in the Ge-rich alloy. Laser and ion irradiated stoichiometric alloy exhibits lower stability with respect to the sputtered film while irradiated amorphous Te-rich samples are more stable than the as deposited amorphous sample. An enhancement of edge-sharing GeTe4 tetrahedra Raman signal at the expenses of Ge-rich tetrahedra signal occurs in the irradiated samples with respect to the as-deposited amorphous layers both in the stoichiometric and in the Te-rich alloy. The crystallization temperature decreases in GeTe since the system during irradiation is promoted to a state closer to the crystalline phase while in Te-rich alloy the stability increases with the density of Ge-Te bonds since this local rearrangement delays Te precipitation and the subsequent GeTe crystallization. Irradiation does not affect the stability of Ge rich alloy in which crystallization is limited by the Ge mobility and the induced local rearrangements is probably prevented by the low atomic diffusivity. INTRODUCTION GeTe system belongs to IV-VI compound semiconductors and it is characterized by fast crystallization and high stability of the amorphous phase. Because of its higher crystallization temperature (~170°C), compared with other chalcogenide alloys (Ge2Sb2Te5~130°C), GeTe has been suggested as active medium in devices with high operating temperature. GeTe is also the basic ingredient of a class of materials, GeTe–Sb2Te3 ternary alloys, employed as active medium in optical and electrical data storage devices [1]. Therefore the comprehension of the link between local order, stoichiometry and crystallization rate in the simple binary alloy could clarify the microscopic processes occurring in the more complex ternary alloys [2,3]. Moreover for a given alloy composition, the crystallization kinetics is strongly affected by the local atomic arrangement and chemical bonding of the amorphous network [4,5] and then it’s also important to understand how this order varies changing the amorphous state by means of ion or laser
irradiation [6,7]. In this work we investigate Ge1-xTex (x=0.37, 0.51, 0.64) alloys and present data on the variation of the crystallization kinetics with the film composition and amorphous state to correlate them to the local order analyzed by micro-
Data Loading...
