Germanium vacancy centre formation in CVD nanocrystalline diamond using a solid dopant source

Abstract

We report the in-situ formation of germanium vacancy (GeV) centres in nanocrystalline diamond (NCD) using chemical vapor deposition (CVD) technique. Commercial Ge wafers are used as the solid dopant source and as substrate. The hydrogen-rich plasma (1% CH4 in H2, 3000 W and 45 Torr, ASTeX 6500 series deposition system) etches the Ge substrate and introduces the GeV complex in the NCD layer. As themelting proximity of Ge and CVD diamond growth temperature introduces limitations; the NCD depositions are restricted to (720 ± 20)°C. Scanning electron microscopy reveal randomly facetted film morphology and Raman measurements confirm diamond formation under the chosen deposition conditions. We discuss an additional challenge, the absence of carbide layer at the Ge-NCD interface, potentially limiting film adhesion to the Ge substrate but at the same time demonstrate self-delaminating free-standing multicrystalline diamond films. Qualitative analysis using time of flight secondary mass ion spectroscopy confirms Ge incorporation, and room temperature photoluminescence (PL) measurements confirm local GeV ensemble formation in diamond films as indicated by the 602 nm PL peak. We also discuss the challenges in using NCD, present low-temperature (10K) PL results and assign strain to explain GeV peak shifts in such material.