Ge with a quasi-direct band gap can be realized by strain engineering, alloying with Sn, or ultrahigh n-type doping. In this work, we use all three approaches together to fabricate direct-band-gap Ge-Sn alloys. The heavily doped n-type Ge-Sn is realized with CMOS-compatible nonequilibrium material processing. P is used to form highly doped n-type Ge-Sn layers and to modify the lattice parameter of P-doped Ge-Sn alloys. The strain engineering in heavily-P-doped Ge-Sn films is confirmed by x-ray diffraction and micro Raman spectroscopy. The change of the band gap in P-doped Ge-Sn alloy as a function of P concentration is theoretically predicted by density functional theory and experimentally verified by near-infrared spectroscopic ellipsometry. According to the shift of the absorption edge, it is shown that for an electron concentration greater than 1x10^20 cm-3 the band-gap renormalization is partially compensated by the Burstein-Moss effect. These results indicate that Ge-based materials have high potential for use in near-infrared optoelectronic devices, fully compatible with CMOS technology.
@article{arxiv.1901.01721,
title = {Strain and Band-Gap Engineering in Ge-Sn Alloys via P Doping},
author = {Slawomir Prucnal and Yonder Berencén and Mao Wang and Jörg Grenzer and Matthias Voelskow and Rene Hübner and Yuji Yamamoto and Alexander Scheit and Florian Bärwolf and Vitaly Zviagin and Rüdiger Schmidt-Grund and Marius Grundmann and Jerzy Żuk and Marcin Turek and Andrzej Droździel and Krzysztof Pyszniak and Robert Kudrawiec and Maciej P. Polak and Lars Rebohle and Wolfgang Skorupa and Manfred Helm and Shengqiang Zhou},
journal= {arXiv preprint arXiv:1901.01721},
year = {2019}
}