Ge24.9Sb11.6S63.5 thin films aged under various conditions

Introduction Although the chalcogenide glasses and amorphous thin films find application in a number of fields, the limitation of such materials could be the uncontrolled drift in their exploitation characteristics over... [ view full abstract ]

Introduction

Although the chalcogenide glasses and amorphous thin films find application in a number of fields, the limitation of such materials could be the uncontrolled drift in their exploitation characteristics over time. This means that the properties can vary over a period of time as the state tries to reach a more energetically favorable state. This phenomenon is known as ageing and restricts the wider practical implementation of these materials.

Methods

Amorphous Ge_24.9Sb_11.6S_63.5 thin films prepared by thermal evaporation were aged for more than 1 year under various conditions: in a dark in a desiccator (DES), in a dark and humid atmosphere (RH75) and under laboratory conditions under daylight (SUN). Changes in thin films during/due to ageing were studied by the EDX analysis, FTIR spectroscopy, AFM and ellipsometry. The photo-sensitivity of virgin thin film and variously stored thin films during the ageing was also compared.

Results and Discussion

The bleaching of thin films (the blue shift of the optical band gap) was observed with the magnitude depending on the storage conditions. The lowest magnitude of bleaching was observed for the thin films stored in a dark in a desiccator, while the highest magnitude of bleaching was observed for the thin films stored under laboratory conditions under daylight. The overall kinetics of ageing (bleaching) follow well the stretch-exponential function with the formal rate depending on the storage conditions and the stretch parameter slightly varying in the region of 0.54 – 0.6. This means that during the aging of films in various types of storages the effective dimensionality of the samples is not changing. The photo-sensitivity of the aged thin films was significantly affected by storage conditions and was found to decrease with the increasing time of ageing.