Here we report a method for improving the magnetic field sensitivity of an ensemble of Nitrogen-Vacancy (NV) centres in 12 C-enriched diamond aligned along the [111] crystal axis. The preferentially-aligned NV centres are fabricated by a Plasma Enhanced Chemical Vapour Deposition (PECVD) process and their concentration is quantitatively determined by analysing the confocal microscopy images. We further observe that annealing the samples at high temperature (1500 °C) in vacuum leads to a conversion of substitutional nitrogen into NV centres. This treatment also increases the coherence time of the NV centres electron spins up to 40 μs, which corresponds to enhancement of the sensitivity by a factor of three. However, this procedure also leads to a loss of the preferential alignment by 34%.

The growth of single-crystalline high-quality zinc oxide (ZnO) layers by a methane (CH 4 )-based chemical vapor deposition (CVD) growth process on sapphire substrates with an aluminum nitride (AlN) nucleation layer was investigated. We achieved monocrystalline ZnO layers free of rotational domains, which show in high-resolution X-ray diffraction (HRXRD) measurements a very narrow (∼110 arcsec) full width at halfmaximum (fwhm) in ω scans for the ZnO (0002) reflection. The influence of growth time and layer thickness on crystal properties such as surface roughness, dislocation density, and optical properties was investigated. We find low edge and screw dislocation densities of around 6.4 × 10 8 and 2.1 × 10 7 cm −2 , respectively. In low-temperature photoluminescence (PL) spectra the fwhm of the donor-bound exciton emission drops to about 170 μeV for increasing layer thickness. Moreover, these layers have a smooth surface with a surface roughness RMS value of 4 nm and a very low donor concentration of about 1.7 × 10 15 cm −3 . We also studied the influence of substrate miscut on crystal growth properties and found no significant influence. The results prove the high potential of methane-based chemical vapor deposition for the production of high-quality ZnO layers.

In this work, we report on three new extremely sharp emission lines in zinc oxide (ZnO) related to iron–lithium complexes. The identification is based on a comparison of hydrothermally grown ZnO with high lithium concentration and a lithium-free sample grown by methane based chemical vapor deposition, which both were implanted with iron. After annealing in a mixed oxygen/argon atmosphere at 800°C, the lithium-free sample showed no additional lines besides the well-known emission at 693nm (1.78734eV), whereas the hydrothermally grown sample emitted three intense and sharp lines in photoluminescence (PL) spectroscopy. These emission lines at 705nm (1.75873eV), 712nm (1.74153eV), and 732nm (1.69283eV) were characterized by temperature dependent high resolution continuous wave (cw) and time-resolved PL spectroscopy, as well as by photoluminescence excitation spectroscopy, and are assigned to different Fe–Li complexes. We find a single thermally activated excited state for each of the complex emission lines, different from the 4T1→6A1 transition of Fe3+ with its at least three excited states. While time-resolved photoluminescence measurements of the Fe3+ transition show a lifetime of 24.9±0.5ms, we find a reduced lifetime of 8.5±1ms for the new zero phonon lines, pointing to stronger mixture of the Fe 3d states with surrounding p-orbitals.

In this work, internal [Formula: see text]T[Formula: see text]A[Formula: see text] transitions within the half-filled 3d shell of Fe[Formula: see text] in extremely pure chemical vapor deposition (CVD)-grown ZnO layers were investigated by means of high-resolution, low-temperature continuous wave (cw) photoluminescence (PL), time-resolved PL, photoluminescence excitation (PLE) spectroscopy, Zeeman spectroscopy, and deep level transient spectroscopy (DLTS). For comparison, Zeeman spectroscopy measurements were also performed on commercially available, hydrothermally grown ZnO bulk crystals. Magnetic fields up to [Formula: see text] were applied parallel and perpendicular to the c-axis of the ZnO crystals in order to investigate the fine structure of included states. The splitting pattern of emission lines related to [Formula: see text]T[Formula: see text] [Formula: see text] [Formula: see text]A[Formula: see text] Fe[Formula: see text] transitions was theoretically modeled by a Hamiltonian matrix including the crystal field in cubic and trigonal symmetries and spin–orbit interaction for the complete excited [Formula: see text]T[Formula: see text] state. The extremely pure ZnO used in this study, in direct comparison to hydrothermally grown ZnO, allows the identification, investigation, and description of single isolated Fe[Formula: see text] defects in ZnO for the first time—different from literature reports hitherto, which seemingly were recording data on Fe–Li complexes. The resulting exact energy-level scheme in combination with the experimental data leads to a re-evaluation of [Formula: see text]T[Formula: see text] [Formula: see text] [Formula: see text]A[Formula: see text] Fe[Formula: see text] transitions in ZnO.