SKM 2023 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 18: Optical Properties (joint session HL/CPP)

HL 18.1: Talk

Tuesday, March 28, 2023, 09:30–09:45, POT 112

Can Ge and Si be optoelectronic materials: Hexagonal polytypes — •Martin Keller¹, Abderrezak Belabbes^1,2, Jürgen Furthmüller¹, Friedhelm Bechstedt¹, and Silvana Botti¹ — ¹Friedrich-Schiller-Universität Jena, Institut für Festkörpertheorie und -optik, Max-Wien-Platz 1, 07743 Jena, Germany — ²Department of Physics, Sultan Qaboos University, P.O. Box 36, PC 123, Muscat, Oman

The group IV elements silicon and germanium crystallize in cubic diamond structure under ambient conditions and feature indirect bandgaps. Therefore they cannot emit light efficiently and are not applicable in active optoelectronic devices. Under high pressure, however, as well as using different growth techniques, several Si and Ge polymorphs, including hexagonal polytypes, have been observed. Lonsdaleite Ge as well as Ge-rich hexagonal alloys have even been found to have a direct bandgap and strongly emit light with varying frequency. Thus hexagonal systems have become of great interest for potential optical emitters that may be integratable with CMOS technology. We have performed extensive ab initio studies of the energetic, structural, elastic and electronic properties as well as the strengths of some dipole transitions of the hexagonal Si and Ge polytypes 2H, 4H and 6H using Density Functional Theory and approximate quasiparticle treatments, and trends between the different geometries are analysed. The results for cubic and hexagonal Si and Ge agree excellently with existing experimental findings. The electronic structures point to promising optical properties.