​By Jérémie Chrétien
Silicon Nanoelectronics Photonics and Structures Team (SiNaPS)

Due to the direct band gap, semiconductors based on the germanium-tin alloy (GeSn) are the subject of special care for opto-electronic devices. Unlike pure germanium, unstrained GeSn alloys have a direct inter-band energy transition from a concentration of around 6 %, providing an optical gain necessary to observe the laser effect at low temperatures. The operating temperature of the laser effect is increasing with the tin content. However, alloying tin in germanium faces technological issues in terms of material growth for a concentration higher than 16 %. The application of a tensile strain can be an alternative approach to modify the band diagram and amplify the material gain in order to consider applications at room temperature.
In a first chapter, useful quantities and effects of the deformation on the band structure are introduced. GeSn alloys under bi-axial tensile strain are studied in micro-disk cavites stressed by tensor layer, and then in suspended cross-like membranes using strain management. The strain is estimated by FEM simulation, Raman spectroscopy and photoluminescence. The laser effect is also shown.
In a final chapter, [100] uni-axial tensile strain is presented in micro-bridge structures, demonstrating the laser effect up to 273 K. Thanks to micro-laue diffraction, a tensile strain measurement is also carried out.