Thesis: Study of non-stoichiometric III-V semiconductors for sampling microwave signals
Thomas Demonchaux
Thesis defence16 May 2018 at 10:30 a.m.
IEMN Amphitheatre - Villeneuve d'Ascq
Abstract:
Discovered in the late 1980s, low-temperature epitaxial gallium arsenide (GaAs-BT) has interesting properties for optoelectronic applications. Its properties are closely linked to the presence of point defects, the deep levels of which give lifetimes compatible with its use as an active layer in photo-switches. With the aim of improving current knowledge of the physical origin of the lifetime and thus optimising it, this thesis work involved carrying out an in-depth study of the material, in particular by combining macroscopic analyses with microscopic characterisation. It is divided into five chapters, the first of which presents the current state of knowledge of GaAs-BT, while the second describes the various techniques used in this study. The third chapter looks at the chemical composition of the low-temperature epitaxial layer and its structural characterisation by X-ray diffractometry. It reveals the growth of ternary or quaternary compounds highly diluted in phosphorus and indium and suggests the presence of V-element antisites. The presence of phosphorus raises the question of the chemical nature of these antisites. The next chapter aims to identify the point defects embedded in the material using low-temperature scanning tunneling microscopy. Although the majority of the defects differ from the antisites observed in the literature by having a negative charge state and a changing appearance when the tip passes through, an analysis of the imaging conditions as a function of temperature combined with ab-initio calculations indicates the preferential formation of arsenic antisites compared with phosphorus antisites. The final chapter is devoted to the characterisation of the material after annealing. The particularity of this section lies in the discovery that the antisites do not precipitate at a growth temperature of 325°C and therefore give the most interesting lifetimes for the desired applications.
Jury members :
| Mr Alain Le Corre Mr Georges Bremond Mr Didier Stiévenard Mr Stéphane Formont Mr Bruno Grandidier Mr Xavier Wallart |
Professor, INSA Rennes Professor, INSA Lyon Director of Research, CNRS, IEMN Engineer, Thalès Director of Research, CNRS, IEMN Director of Research, CNRS, IEMN |
Rapporteur Rapporteur Member Member Director Co-director |
