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Séminaire Optique : lundi 12 juin 2023 à 11h00

Alain Dijkstra  (Walter Schottky Institute, TU Munich, Germany)

Titre : Surprisingly efficient emission from Hexagonial Germanium


Institut Néel, Salle E424 (Louis Weil)

Résumé : Silicon is and has been the workhorse of the semiconductor industry for decades. Despite its excellent electrical properties, its optical properties are limited because of its indirect bandgap. Neither can any of the other chemically well-matched group-IV elements emit light efficiently in their natural crystal structures. However, in recent years it has been demonstrated that by alloy- and crystal-phase engineering direct bandgap semiconductors can be made out of group-IV elements, i.e. GeSn-alloys and of course Hexagonal-SiGe alloys. These materials promise close integration of optical and electrical elements compatible with the vast silicon technology.

For Hex-Ge it has been explicitly shown that it exhibits a direct bandgap based on the analysis of photoluminescence spectra. In addition, sub-nanosecond radiative lifetimes, and therefore efficient light emission, have been measured for Hex-Si0.2Ge0.8 . This leaves the optical efficiency of Hex-Ge still unknown.

In this talk I will take you through the current knowledge that we have of the Hex-SiGe material system and in particular Hex-Ge. In particular, I will show three techniques we have used to estimate the efficiency of light emission in Hex-Ge and find that it is, surprisingly, very close to that of Hex-Si0.2Ge0.8. First, we compare the overall photoluminescence intensities measured on ensembles of NWs. Second, we have used an improved Lasher-Stern-Würfel-model (LSW) based fitting routine, on the photoluminescence spectra of a low-temperature excitation-density series. Third, a direct measurement of the carrier relaxation time has been realized using reflective differential picosecond pump-probe spectroscopy. We will find that Hex-Ge is surprisingly efficient.