(Invited) Direct Band Gap Emission from Hexagonal Si-Ge

Abstract

Silicon and germanium cannot emit light efficiently due to their indirect bandgap, hampering the development of Si-based photonics. However, alloys of SiGe in the hexagonal phase are predicted to have a direct band gap. In this work, we exploit the unique feature of the nanowire growth mechanism to control the crystal structure by tuning the contact angle of the catalyst particle. A wurtzite wire is used as an epitaxial template to realise hexagonal Ge, SiGe, or pure Si (see accompanying Figure).1,2 We show efficient light emission up to room temperature accompanied by a short radiative life time, the hallmarks of a direct band gap material.3 The band gap energy is tunable in the range of 0.35 till 0.7eV by the chemical composition, opening a plethora of new applications. In addition, first signatures of lasing from hexagonal SiGe are obtained using an external cavity. We finally discuss possible routes to integrate this material in Si- technology. 1H.I.T Hauge et al., Nano Letters 15, 5855 (2015). 2H.I.T Hauge et al., Nano Letters 17, 85 (2017). 3E.M.T. Fadaly et al., Nature 580, 205 (2020). Figure 1