Germanium-Vacancy Color Center Research Articles

Formation of Ge-V color centers in poly- and monocrystalline CVD diamond: A comparative study

Germanium-Vacancy (Ge-V) color centers in diamond have narrow-band photoluminescence (PL) at room temperature (RT) and attract considerable attention due to their possible application in quantum information technologies, biomedicine, and local optical thermometry. In this work, we used microwave plasma chemical vapor deposition (MPCVD) to synthesize Ge-doped polycrystalline diamond (PCD) films and single-crystal diamond (SCD) epitaxial layers in hydrogen-methane-germane gas mixtures. Thick (>100 μm) layers of both types were grown to analyze their structure and luminescence characteristics. The first demonstration of the absorption of Ge-V centers in both PCD and SCD materials at low temperatures is presented. The sufficient narrowing of the Ge-V PL line for the SCD sample in comparison with the PCD sample was observed. On the other hand, the intensity of the Ge-V signal was an order of magnitude higher in the PCD sample compared to the SCD sample. A set of single Ge-V centers formed during CVD has been demonstrated. The results obtained can be used to manufacture and design various photonic devices based on Ge-V color centers.

Optical properties of SiV and GeV color centers in nanodiamonds under hydrostatic pressures up to 180 GPa

The silicon-vacancy (SiV) and germanium-vacancy (GeV) centers in diamond have a sharp photoluminescence with high brightness. In this work, the photoluminescence of these centers is measured up to 180 GPa using nanodiamonds integrated in a diamond anvil cell. The results show blueshifts in the mean emission energy determined by the atomic radii of the impurity. The agreement with $a\phantom{\rule{0}{0ex}}b$ $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ calculations based on the lattice compression of diamond demonstrates the potential of these centers for sensing under extreme pressure conditions.

Quantum Interference of Resonance Fluorescence from Germanium-Vacancy Color Centers in Diamond

Resonance fluorescence from a quantum emitter is an ideal source to extract indistinguishable photons. By using the cross-polarization to suppress the laser scattering, we observed resonance fluorescence from GeV color centers in diamond at cryogenic temperature. The Fourier-transform-limited line width emission with T2/2T1 ∼ 0.86 allows for two-photon interference based on single GeV color center. Under pulsed excitation, the separated photons exhibit a Hong-Ou-Mandel quantum interference above classical limit, whereas the continuous-wave excitation leads to a coalescence time window of 1.05 radiative lifetime. In addition, we demonstrated a single-shot readout of spin states with a fidelity of 74%. Our experiments lay down the foundation for building a quantum network with GeV color centers in diamond.

Theoretical study on the formation of diamond germanium vacancy color center

Germanium-vacancy (GeV) color centers in diamond are superior to other color centers in terms of luminescence intensity. The Ge-doping process is key to the successful preparation of GeV color centers in diamond. In this study, the formation mechanism of GeV color centers is explored via first-principles calculations of the adsorption and migration of Ge on the (001) surface of diamond. The results reveal that Ge atoms on the surface of completely hydrogenated diamond have a negative adsorption energy, indicating that they cannot be adsorbed. In contrast, the adsorption energy of Ge atoms on the surface of non-perhydrogenated diamond is relatively large, which indicates that the surface of non-perhydrogenated diamond can adsorb Ge atoms. When Ge atoms are closer to hydrogen defects, their adsorption energy is greater. As the extent of hydrogen deficiency increases, the overall adsorption energy increases accordingly. The hydrogen deficiency of the diamond surface may determine the extent of the Ge content on the diamond surface. Magnetic moment, differential charge, and Bader analyses reveal that charge is transferred between Ge and carbon atoms on the diamond surface. In addition, the Ge and carbon atoms form covalent bonds at positions where the adsorption energy is maximum. Finally, the migration of Ge atoms on the diamond surface enables them to reach a stable position easily.

Principle study of structure, energetics, and electrical properties of Ge-N-vacancy complexes in diamond

Following first principles and inspired by the special structure of the nickel–nitrogen color center, this work enhances the known diamond germanium-vacancy (GeV) color center by adding nitrogen (N) atoms and increasing the number of vacancies. Results demonstrate that the most stable structure is one without vacancies, where the germanium (Ge) atoms are connected to four N atoms. This work analyzes the new structure of the GeV color center and determines the charge transfer and bonding from the difference in charge density. The electron bands and density of states of the GeV color center with four N atoms are calculated. By analyzing the electrical properties of each atom, we posit that the N atom is a transitional modified atom. The new structure of the GeV color center has good prospects for use in sensors and single-photon sources.

Stochastic superflares of photoluminescence from a single microdiamond with germanium-vacancy color centers: A general phenomenon or a unique observation

We report the discovery of a GeV-associated phenomenon which is strong (up to an order) stochastic reversible enhancements of photoluminescence intensity in a single GeV diamond synthesized with the high-pressure, high-temperature technique. We were lucky to observe this effect with only one crystal among dozens of similar microdiamonds. Each rise and fall of the intensity above its stable moderate level may be referred to as a superflare with smooth dynamics of the transients which develop on the timescale of seconds. These flares tend to recur infinitely at ambient conditions under cw-laser excitation above a certain input power threshold. To explain this phenomenon we propose a theory of intrinsic optical instabilities which develop in a dense ensemble of quantum emitters.

Photoluminescence of Germanium-Vacancy Color Centers in Diamond Particles Obtained by Chemical Vapor Deposition

We synthesized diamond particles with germanium-vacancy color centers on a germanium substrate by hot-filament chemical vapor deposition. The formation of color centers occurred during the growth of diamond particles by the introduction of germanium atoms formed by the etching of a crystalline germanium wafer with atomic hydrogen. The conditions of the vapor phase deposition, which affect the photoluminescence of germanium-vacancy color centers in diamond particles, are considered. The highest photoluminescence intensity of germanium-vacancy color centers was achieved for diamond particles obtained on a substrate at a temperature of its surface close to the melting point of germanium. In the photoluminescence spectra of diamond particles, we also observed the lines presumably related to optical centers including tu-ngsten.

Фотолюминесценция центров окраски германий-вакансия в полученных химическим газофазным осаждением алмазных частицах

Hot Filament Chemical Vapor Deposition technique was used to synthesize diamond particles with germanium-vacancy color centers on a germanium substrate. The formation of color centers occurred during the growth of diamond particles due to the incorporation of germanium atoms formed as a result of a crystalline germanium wafer etching with atomic hydrogen. The conditions of Chemical Vapor Deposition process which affect the photoluminescence of color centers of germanium vacancy in diamond particles, are considered. The highest photoluminescence intensity of germanium-vacancy color centers was achieved for diamond particles obtained on a substrate at a surface temperature close to the melting temperature of germanium. The photoluminescence spectra of the diamond particles also showed lines presumably associated with the optical centers which contain tungsten.

Bottom up engineering of single crystal diamond membranes with germanium vacancy color centers

Color centers in diamond have garnered significant attention for applications in integrated quantum photonics. The availability of thin (∼ hundred of nanometers) diamond membranes is paramount to achieve this goal. In this paper, we describe in detail a robust, reproducible and cost effective fabrication method that enables engineering high quality thin diamond membranes with uniform distribution of germanium vacancies employing microwave plasma chemical vapor deposition. We use a combination of different germanium precursors for homogeneous doping of the membranes to increase the probability of germanium incorporation into the diamond lattice. Our fabrication methodology can be further extended to implementation of other color centers in thin diamond membranes and be used for engineering quantum photonic devices.

Optical bistability and multistability induced by quantum coherence in diamond germanium-vacancy color centers.

Optical bistability (OB) and optical multistability (OM) behaviors are investigated theoretically in a four-level N-type diamond germanium-vacancy (GeV) color center scheme immersed in a unidirectional ring cavity based on electromagnetically induced transparency (EIT). It is found that OB behavior is very sensitive to the system parameters, such as the detunings of probe and coupling fields and the intensities of coupling fields as well as the density of GeV centers, and the thresholds of OB can be controlled via changing these parameters. In addition, we can switch OB to OM by adjusting the intensity of control field and the density of GeV centers or vice versa. Our results may provide some guidance for an all-optical switching, optical communications, and optical logic devices in a solid-state system.

Formation of GeV, SiV, and NV Color Centers in Single Crystal Diamond Needles Grown by Chemical Vapor Deposition

Herein the color centers formation in diamond crystallites of pyramidal shape grown by chemical vapor deposition (CVD) is described. The individual crystallites are extracted from polycrystalline films grown on silicon substrates. The silicon‐vacancy (SiV), germanium‐vacancy (GeV), and nitrogen‐vacancy (NV) centers are created by introducing corresponding precursors from substrate material, gaseous nitrogen, and thermally evaporated germanium added during CVD. Some amount of NV centers detected in all types of the diamond crystallites is assigned to uncontrollable presence of nitrogen in the CVD reactor. The low temperature photoluminescence spectra indicate presence of ensembles of SiV centers in diamond structure. The SiV centers are concentrated predominantly at apexes of the diamond crystallites located at substrate surface. Intense growth of CN radicals in plasma‐activated gas environment during CVD process is detected after nitrogen gas addition. The crystallites obtained with the nitrogen addition demonstrate significant variation of their pyramid angle. The photoluminescence spectra of crystallites grown with nitrogen addition demonstrate increase of both negatively and neutrally charged states of NV color center. The GeV centers are created via thermal evaporation of pure Ge during CVD growth. The photoluminescence spectra of the crystallites grown with Ge addition demonstrate presence of GeV color centers ensemble.

Correction to Germanium-Vacancy Color Center in Diamond as a Temperature Sensor

Correction to Germanium-Vacancy Color Center in Diamond as a Temperature Sensor

Growth of polycrystalline and single-crystal CVD diamonds with bright photoluminescence of Ge-V color centers using germane GeH4 as the dopant source

Germanium-Vacancy (Ge-V) color center in diamond possesses a narrow band photoluminescence (PL) emission in the orange spectral range interesting as a single-photon source for quantum optical technologies and thermometry, therefore, development of methods for the controllable doping of diamond with Ge is of high importance for such applications. Here, we report on the synthesis of polycrystalline and epitaxial single crystal Ge-doped films using microwave plasma chemical vapor deposition (CVD) technique by addition of the germane GeH4 gas into the H2-CH4 plasma. It is demonstrated, that GeH4 addition affects the CVD growth of microcrystalline diamond, reducing the film growth rate and increasing the average diamond grain size. The films show bright photoluminescence of Ge-V centers at ≈602 nm under the optimized GeH4 concentration, with a zero-phonon line width of 1.6 nm (FWHM) for Ge-V ensemble at low temperatures (5 K). The developed in-situ doping from the germane gas opens a way for a better control of the Ge-V color center formation in diamond for photonic applications.

Germanium-Vacancy Color Center in Diamond as a Temperature Sensor

We present high-resolution, all-optical thermometry based on ensembles of GeV color center in diamond. Due to the unique properties of diamond, an all-optical approach using this method opens a way to produce non-invasive, back-action-free temperature measurements in a wide range of temperatures, from a few Kelvin to 1100 Kelvin.

Quantum Nonlinear Optics with a Germanium-Vacancy Color Center in a Nanoscale Diamond Waveguide.

We demonstrate a quantum nanophotonics platform based on germanium-vacancy (GeV) color centers in fiber-coupled diamond nanophotonic waveguides. We show that GeV optical transitions have a high quantum efficiency and are nearly lifetime broadened in such nanophotonic structures. These properties yield an efficient interface between waveguide photons and a single GeV center without the use of a cavity or slow-light waveguide. As a result, a single GeV center reduces waveguide transmission by 18±1% on resonance in a single pass. We use a nanophotonic interferometer to perform homodyne detection of GeV resonance fluorescence. By probing the photon statistics of the output field, we demonstrate that the GeV-waveguide system is nonlinear at the single-photon level.

Germanium–vacancy color center in isotopically enriched diamonds synthesized at high pressures

We report on the high-pressure synthesis of novel nano- and microcrystalline diamonds with germanium–vacancy (Ge–V) color centers emitting at 602 nm. The synthesis was carried out in non-metallic growth systems C–H–Ge and C–H–O–Ge enriched with germanium and carbon isotopes. We demonstrate germanium and carbon isotope shifts in the fine structure of the luminescence, which allows us to unambiguously associate the center with the germanium impurity entering into the diamond lattice. We show that there are two ground-state energy levels with the separation of 0.7 meV and two excited-state levels separated by 4.6 meV in the electronic structure of the center and suggest a split-vacancy structure of this center. High-intensity and narrow-line emission of high-pressure synthesized small diamonds with Ge–V centers makes them promising candidates for single-photon emitters.