Straining Group-IV Vacancy Color Centers in Diamond: A DFT study of the ZPL position and shift

Abstract

Color centers play an important role in the development of diamond based devices, both for quantum technological applications as well as sensing applications. 1 Most elements of the periodic table have been considered as color center in diamond at some point in the past, even lanthanides like Eu, due to their sharp spectral properties. 2 Group-IV color centers have more recently gained attention due to their excellent Debye-Waller factor, making them very suitable for optically based quantum applications. However, practical diamond based devices contain several sources of strain, which result in a shifting of the zero-phonon line depending on the type of strain and magnitude experienced by the color center. 3,4 Using density functional theory calculations, we investigate the impact of isotropic and anisotropic strain on the GeV and SnV centers in diamond, with the aim of understanding the experimentally observed distributions of ZPL positions. Using defect concentrations of 1.5% down to 0.1% (64-1000 atom conventional cells) we show that it is possible to extrapolate to experimentally relevant concentrations. 3,4 The calculated ZPL position and strain-induced shifts are presented for both neutral and negatively charged color centers. For the GeV 0 color center, both red and blue shifts are obtained for isotropic strain, while anisotropic strain only gives rise to a redshift. In case of the latter, the absolute magnitude of the shift is also significantly larger. 3 In case of the SnV 0 and SnV-, the position of the ZPL shows a smaller dependence on the color center concentration. In contrast, the ZPL shift is larger than is obtained for the GeV 0 color center. We also note that the impact of the charge state is rather non-trivial. The calculated results are discussed within the context of the experimental observation of distributions of ZPL positions for the SnV and GeV centers. We highlight some of the pitfalls when comparing calculated and experimental results, and indicate how further experimental-theoretical studies can provide insights into the black box of experimentally doped samples.