Growth and Photoluminescence Studies of Tin Vacancy Centres in CVD Diamond

Scalable quantum networks require nodes that are optically addressable long-lived quantum memories and efficiently integrated into a photonic circuit [1]. A promising candidate is the nitrogen vacancy (NV) centre in diamond due to its outstanding spin coherence at room temperature; however, enhancing its optical performance with nanostructures and stability remains challenging due to the sensitivity of the shallow NV centre to the diamond surface [2]. Potential alternatives are the Group-IV colour centres in diamond that exhibit inversion symmetry and are less affected by first-order electric fluctuations and minimal spectral diffusion [3]. Compared to the silicon and germanium colour centres, the tin vacancy centre in diamond has attracted attention due to its long spin coherence times at temperatures above 1 K, demonstrating its potential to function as quantum nodes [4].<br/><br/>In this study, we report the in-situ fabrication of SnV centres in free-standing (110)-textured microcrystalline diamond (MCD) using the microwave plasma-enhanced chemical vapor deposition technique and tin oxide (SnO₂) as the solid dopant source. Upon ignition of the methane-hydrogen diamond growth plasma, Sn deposits on the substrates. We demonstrate that the resulting CVD diamond growth inhibition can be partially alleviated by placing the substrate and dopant at different heights. Room temperature photoluminescence (PL) measurements (λ_exc = 512 nm, 1 mW) confirm SnV formation in MCD as indicated by the zero phonon line (ZPL) at 620 nm. In addition to the ZPL, PL peak at 631 nm that correspond to the bound Sn in the diamond lattice are also observed [5]. Scanning electron microscopy analysis shows growth temperature-dependent surface morphology of the overgrown CVD diamond layer. We report that an optimal substrate temperature of 750 °C leads to a higher SnV density per unit surface area, and corroborate this observation with SnV formation in different growth sectors present in the diamond film.<br/><br/><b>References</b><br/>[1] S.L. Mouradian <i>et al.</i>, Scalable Integration of Long-Lived Quantum Memories into a Photonic Circuit, <i>Phys. Rev. X</i> <b>5</b>, 031009 (2015).<br/>[2] L.V.H. Rodgers <i>et al.</i>, Materials Challenges for Quantum Technologies Based on Color Centers in Diamond. <i>MRS Bull.</i> <b>46</b>/7, 623–633<b> (</b>2021).<br/>[3] T. Iwasaki, Color Centers Based on Heavy Group-IV Elements. In <i>Semiconductors and Semimetals</i> <b>103</b>, 237–256 (2020).<br/>[4] M.E. Trusheim <i>et al.</i>, Transform-Limited Photons from a Coherent Tin-Vacancy Spin in Diamond, <i>Phys. Rev. Lett.</i> <b>124</b>, 023602 (2020).<br/>[5] S. Tchernij <i>et al.</i>, Single-Photon-Emitting Optical Centers in Diamond Fabricated upon Sn Implantation, <i>ACS Photonics</i> <b>4</b>, 2580 (2017).