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The Journal of Physical Chemistry C

Microscopic Insight into the Inhomogeneous Broadening of Zero-Phonon Lines of GeV– Color Centers in Chemical Vapor Deposition Diamond Films Synthesized from Gaseous Germane

Ivan Yu. Eremchev, Arthur Yu. Neliubov, Kirill N. Boldyrev, Victor Ralchenko, Vadim Sedov, L. Kador, А. В. Наумов

Published Jul 30, 2021• 18 citations
Publisher

Abstract

Diamonds with impurity color centers are a novel class of functional materials with potential for various photonics applications such as quantum optics, metrology, sensorics, and life sciences. When introducing defect centers, a broad range of questions arises about the nature of the photophysical processes in the new materials, in particular regarding the relationship between spectral and morphological properties. Here we present results of comprehensive spectroscopic studies on diamond films with germanium-vacancy (GeV – ) centers, synthesized by chemical vapor deposition from gaseous germane (GeH 4 ). The combination of different techniques (emission and fluorescence excitation spectroscopy, epi-microscopy, and nanoscopy up to the single-emitter level) at room and cryogenic temperatures has shed light onto the spatial distribution of the spectral properties of the GeV – centers in different microregions of the diamond crystal and its relation to local strain/stress. We demonstrate a clear correlation between inhomogeneous broadening and morphological heterogeneities of the sample. Ultranarrow (tens of MHz) stable zero-phonon lines have been observed, which are a prerequisite for various applications.

DOI
10.1021/acs.jpcc.1c02617

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Diamonds with impurity color centers are a novel class of functional materials with potential for various photonics applications such as quantum optics, metrology, sensorics, and life sciences. When introducing defect centers, a broad range of questions arises about the nature of the photophysical processes in the new materials, in particular regarding the relationship between spectral and morphological properties. Here we present results of comprehensive spectroscopic studies on diamond films with germanium-vacancy (GeV – ) centers, synthesized by chemical vapor deposition from gaseous germane (GeH 4 ). The combination of different techniques (emission and fluorescence excitation spectroscopy, epi-microscopy, and nanoscopy up to the single-emitter level) at room and cryogenic temperatures has shed light onto the spatial distribution of the spectral properties of the GeV – centers in different microregions of the diamond crystal and its relation to local strain/stress. We demonstrate a clear correlation between inhomogeneous broadening and morphological heterogeneities of the sample. Ultranarrow (tens of MHz) stable zero-phonon lines have been observed, which are a prerequisite for various applications.
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Delta-Doped GeV−^-− in diamond with isotope resolvable optical spectra
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The silicon-vacancy (SiV) color center in diamond is a solid-state single photon emitter and spin quantum bit suited as a component in quantum devices. Here, we show that SiV centers in nanodiamonds exhibit a strongly inhomogeneous distribution with regard to the center wavelengths and linewidths of the zero-phonon-line (ZPL) emission at room temperature. We find that the SiV centers separate in two clusters: one group exhibits ZPLs with center wavelengths within a narrow range ≈730–742 nm and broad linewidths between 5 and 17 nm, whereas the second group comprises a very broad distribution of center wavelengths between 715 and 835 nm, but narrow linewidths from below 1 up to 4 nm. Supported by ab initio Kohn–Sham density functional theory calculations we show that the ZPL shifts of the first group are consistently explained by strain in the diamond lattice. Further, we suggest, that the second group showing the strongly inhomogeneous distribution of center wavelengths might be comprised of a new class of silicon-related defects. Whereas single photon emission is demonstrated for defect centers of both clusters, we show that emitters from different clusters show different spectroscopic features such as variations of the phonon sideband spectra and different blinking dynamics.
Color centers in diamond are widely recognized as a promising solid state platform for quantum cryptography and quantum information processing. For these applications, single photon sources with a high intensity and reproducible fabrication methods are required. Here, we report a novel color center in diamond, composed of a germanium (Ge) and a vacancy (V) and named the GeV center, which has a sharp and strong photoluminescence band with a zero-phonon line at 602 nm at room temperature. We demonstrate this new color center works as a single photon source. Both ion implantation and chemical vapor deposition techniques enabled fabrication of GeV centers in diamond. A first-principles calculation revealed the atomic crystal structure and energy levels of the GeV center.
Progress in controlling diamond synthesis has made it possible to produce very pure crystals and to incorporate and control atomic impurities and carbon vacancies in the crystal lattice. The appropriate impurity-vacancy combinations can give rise to special defects known as color centers, such as the nitrogen-vacancy (NV) or the silicon-vacancy (SiV), which exhibit exceptional quantum properties with spins that are optically addressable. The use of diamond containing color centers has paved the way for the development of innovative quantum technologies, such as very high-resolution magnetometry and quantum information processing. Nevertheless, the development of quantum sensors at the nanometric scale remains one of the most interesting challenges. In this context, the development of a reliable nanoparticle synthesis technique that allows the desired defects to be incorporated and their quantum optical properties to be modulated is crucial. In this seminar, an efficient and recent method to produce diamond nanoparticles containing NV, SiV and germanium-vacancy (GeV) centers is proposed through direct plasma assisted chemical vapour deposition (CVD) growth. This technique allows good control of both nanoparticle growth processes and color centers formation. The optimization of the CVD nanodiamond growth process is presented, showing the impact of different plasma parameters and gas phasecomposition on nanoparticle crystallinity, size and shape. Morphological characterizations reveal the production of small (around 100 nm) and well faceted nanodiamond particles. In addition, the SiV and GeV color centers incorporation can be tuned within this material by varying the gas phase composition which emphasizes the high flexibility of the CVD growth technique. Finally, the quantum properties of the incorporated color centers have been successfully investigated under extreme pressure conditions (up to ~ 180 GPa) showing a monotonic blue shift of their optical zero-phonon line. Since their luminescence remains stable, SiV and GeV centers emerge as high-pressure nanosensors.