Investigation of the phase change properties of pulsed laser deposited germanium antimony thin films

Abstract

Phase change materials (PCM), such as Ge, Sb and Te alloys, are materials that can switch very fast between two stable states, namely their amorphous and the crystalline phases. In addition to the interest in their physical properties, they are used in many modern technological domains such as data storage and offer great potential for non-volatile electronic memory applications. However, a good control of the stoichiometry and nanostructure of such compound materials is needed to ensure good device operation. The main goal of this thesis is to grow high quality phase change germanium antimony thin films (Ge15Sb85) by Pulsed Laser Deposition (PLD). The aim is to obtain amorphous films at room temperature with the correct chemical content that show phase change behavior. Experimental growth parameters deposition pressure, laser energy and deposition time are varied to that end. Several characterization techniques are used to determine the properties of the films: X-Ray Diffraction (XRD) to investigate the crystal structure of the films and determine their phases (amorphous or crystal), Scanning Electron Microscope (SEM) and Rutherford Back Scattering (RBS) to study the surface morphology and the composition of the films respectively. In addition, electrical measurements are performed, by measuring the sheet resistance as a function of temperature using a two probe method. The amorphous to crystalline phase transition temperature, the electrical energy gap and the behavior of the film after repeated cycles of cooling and heating are thus investigated. Optical measurements using UV-VIS-NIR spectroscopy are performed to determine the optical band gap. Finally, Raman spectroscopy measurements were also achieved to investigate the bonding in the as-deposited and annealed films.