Diamond hosts a wide variety of colour centres that have demonstrated outstanding optical and spin properties. Among them, the nitrogen-vacancy (NV) centre is by far the most investigated owing to ...its superior characteristics, which promise the development of highly sophisticated quantum devices, in particular for sensing applications. Nevertheless, harnessing the potential of these centres mainly relies on the availability of high quality and purity diamond single crystals that need to be specially designed and engineered for this purpose. Plasma assisted chemical vapour deposition (CVD) has become a key enabling technology in this field of research. Nitrogen can indeed be directly doped in situ into a high crystalline quality diamond matrix in a controlled way, allowing the production of single isolated centres or ensembles that can potentially be integrated into a device. In this paper we will provide an overview of the requirements for synthesizing 'quantum-grade' diamond films using CVD. These include the reduction of impurities and surrounding spins that limit coherence times, the control of NV density in a wide range of concentrations as well as their spatial localization within the diamond. Enhancing the charge state and preferential orientation of the colour centres is also discussed. These improvements in material fabrication have contributed to positioning diamond as one of the most promising solid-state quantum systems and the first industrial applications in sensing are just starting to emerge.
The use of diamond as a semiconductor material in power electronics applications is held back by the presence of vertical threading dislocations that are believed to deteriorate device performance. ...Reducing their occurrence in single crystal diamond is therefore crucial. Recently we found that thick CVD diamond grown on the inclined plane of a pyramidal-shape substrate can lead to dislocation bending from a 001 to a 110 direction (Tallaire et al., 2013a 1). In this work we further explore this strategy for the growth of thick crystals with low dislocation density. It is shown that the boundary angle between inclined lateral and top faces plays a critical role in preserving bent dislocations during the entire growth run. Indeed under well-chosen growth conditions, a boundary angle of at least 45° ensures that dislocations never intercept the top face and are confined in a lateral sector. We eventually show clear evidence of dislocation density reduction in the crystal using this approach.
Display omitted
•Growth of thick (100)-oriented single crystal CVD diamond with low dislocation density on (100) pyramidal shape substrate.•Evolution of pyramidal shape as function of boron and nitrogen impurities concentration in the gas phase and power/pressure values.•Evolution of growth sector boundary angle and control of direction propagation of dislocation.•Confinement of dislocations in lateral sectors during CVD diamond growth.
The suitability of type IIa diamonds prepared by High Pressure High Temperature (HPHT) in cubic presses at New Diamond Technology was assessed as substrates for the growth of thick detector-grade ...quality Chemically Vapour Deposited (CVD) diamond films. The substrates were found to possess a moderate dislocation density of about 103cm−2 and a reduced amount of residual impurities as compared to standard type Ib crystals. Using these diamonds as seeds for homoepitaxial growth, CVD films with improved structural characteristics were obtained although extended defects could not be completely prevented from forming and propagating. Their performance as detectors for β radiation was however improved leading to almost full charge collection which shows significant improvement as compared to CVD films grown under the same conditions on standard Ib HPHT diamonds. The availability of this new material source opens the way to the fabrication of higher quality CVD material for electronics applications.
Display omitted
•Thick intrinsic CVD films are grown and retrieved from type IIa diamond substrates.•NDT's type IIa substrates have reduced impurity content and dislocation densities.•CVD films grown on NDT substrates show improved characteristics as compared to standard material.•A thick freestanding CVD plate with almost 100% charge collection efficiency is demonstrated.
H2/O2 plasma treatments offer advantages over other etching processes of diamond as a technique to prepare the substrate surface prior to chemical vapor deposition (CVD) diamond growth. It allows ...removing defects induced on the surface by polishing, thus leading to an improved morphology and limiting the stress within the grown crystal. Moreover, they present the advantage to be performed in situ just before the CVD diamond growth. In this work, H2/O2 plasma treatments were performed so that threading dislocations and other defects are etched preferentially, thus leaving typical etch‐pits. The defect densities in several high pressure high temperature (HPHT) and CVD diamond crystals were then quantified and compared; in particular defects originating from polishing could be distinguished from extended defects inside the crystal. Furthermore, the defect density was found to be of the order of 105/cm2 for HPHT crystals, which was approximately one order of magnitude lower than that measured in low cost commercial CVD monocrystals. The use of laser microscopy also allowed observing the morphology, size and depth of different etch‐pits of 〈001〉‐oriented and misoriented crystals and their evolution with etching time in order to get a better understanding of defect density and formation during CVD growth.
Advanced characterizations with combined analytical tools were carried out at the different stages of diamond heteroepitaxy on Ir/STO/Si (001) substrates. HRTEM and STEM-EELS revealed the presence of ...epitaxial nanometric diamond crystals after bias enhanced nucleation. UV Raman allowed estimating the diamond film quality and its strain at the early stages of heteroepitaxial growth. The crystalline structure and the strain within thick heteroepitaxial films were determined by XRD and CL investigations. A CL study of the cross-section provided the mapping of the dislocation network along the growth direction. Measurements performed on lateral Schottky diodes fabricated on a thick diamond film showed an excellent reproducibility on the substrate with a Schottky barrier height in good agreement with those obtained on homoepitaxial layers.
Display omitted
•Characterizations performed at different stages of heteroepitaxy to relate the electrical properties to the structural ones.•After BEN and without CVD growth, diamond nuclei are evidenced by HRTEM and STEM-EELS•Measurements on lateral Schottky diodes showed an excellent reproducibility on the substrate•Schottky barrier height in good agreement with those obtained on homoepitaxial layers•Heteroepitaxial diamond films show similar boron incorporation efficiency as homoepitaxial ones.
We investigate the potential for optical quantum technologies of Pr3+:Y2O3 in the form of monodisperse spherical nanoparticles. We measured optical inhomogeneous lines of 27 GHz and optical ...homogeneous linewidths of 108 and 315 kHz in particles with 400- and 150-nm average diameters, respectively, for the D21(0)↔H43(0) transition at 1.4 K. Furthermore, ground-state and D21 excited-state hyperfine structures in Y2O3 are here determined by spectral hole burning and modeled by complete Hamiltonian calculations. Ground-state spin transitions have energies of 5.99 and 10.42 MHz, for which we demonstrate spin inhomogeneous linewidths of 42 and 45 kHz, respectively. Spin T2 up to 880μs was obtained for the ±3/2↔±5/2 transition at 10.42 MHz, a value which exceeds that of bulk Pr3+-doped crystals reported so far. These promising results confirm nanoscale Pr3+:Y2O3 is a very appealing candidate to integrate quantum devices. In particular, we discuss the possibility of using this material for realizing spin-photon interfaces emitting indistinguishable single photons.
PDF
