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Solid-state single spins are promising resources for quantum sensing, quantum-information processing and quantum networks, because they are compatible with scalable quantum-device engineering. However, the extension of their coherence times proves challenging. Although enrichment of the spin-zero 12 C and 28 Si isotopes drastically reduces spin-bath decoherence in diamond and silicon, the solid-state environment provides deleterious interactions between the electron spin and the remaining spins of its surrounding. Here we demonstrate, contrary to widespread belief, that an impurity-doped (phosphorus) n-type single-crystal diamond realises remarkably long spin-coherence times. Single electron spins show the longest inhomogeneous spin-dephasing time ( ms) and Hahn-echo spin-coherence time ( T 2 ≈ 2.4 ms) ever observed in room-temperature solid-state systems, leading to the best sensitivities. The extension of coherence times in diamond semiconductor may allow for new applications in quantum technology.

Total photoyield experiments are applied to characterize p-, intrinsic, and n-type diamond with hydrogen-terminated surfaces. On all hydrogen-terminated samples a photoelectron threshold energy of 4.4 eV is detected which is discussed in detail in this letter. We attribute this threshold to the energy gap between the valence-band maximum and the vacuum level, which is 1.1 eV below the conduction-band minimum, and generally referred to as ”negative electron affinity” (NEA). Hydrogen terminated p-type and intrinsic diamond show a rise of secondary photoyield in the excitation regime hν>5.47eV. However, this is not detected on n-type diamond. We ascribe this to the formation of an upward surface band bending in the vicinity of the n-type diamond surface which acts as an energy barrier for electrons.

Nitrogen-vacancy (NV) centers in diamond have attracted significant interest because of their excellent spin and optical characteristics for quantum information and metrology. To take advantage of the characteristics, the precise control of the orientation of the N-V axis in the lattice is essential.Here we show that the orientation of more than 99 % of the NV centers can be aligned along the [111]axis by CVD homoepitaxial growth on (111)-substrates. We also discuss about mechanisms of the alignment. Our result enables a fourfold improvement in magnetic-field sensitivity and opens new avenues to the optimum design of NV center devices.

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n -type doping of (001)-oriented single-crystalline diamond has been achieved using PH3 as doping gas and applying a newly optimized homoepitaxial growth technique based on plasma-enhanced chemical vapor deposition. Hall-effect measurements indicate n-type conductivity with highest mobilities of ∼350cm2∕Vs. Phosphorus doping is confirmed by secondary-ion mass spectroscopy.

The properties of phosphorus incorporation for n-type doping of diamond are discussed and summarized. Doping of (0 0 1)-oriented diamond is introduced and compared with results achieved on (1 1 1) diamond. This review describes detailed procedures and conditions of plasma-enhanced chemical vapour deposition (CVD) growth and characteristics of electrical properties of phosphorus-doped diamond. The phosphorus incorporation was characterized by SIMS analysis including mapping. n-type conductivity is evaluated by Hall-effect measurements over a temperature regime of 300–1000 K. The crystal perfection of (0 0 1)-oriented n-type diamond is also evaluated by x-ray diffraction, Raman spectroscopy, reflection high-energy electron diffraction and cathodoluminescence analyses. The results show that phosphorus atoms are incorporated into the diamond network during (0 0 1) CVD diamond growth and that phosphorus acts as a donor as in (1 1 1)-oriented diamond. This result eliminates the restriction on substrate orientation, which had previously created a bottleneck in the development of diamond electronic devices.

Deposition of hafnium silicate films with various hafnium contents was tried by plasma-enhanced chemical vapor deposition using tetraethoxysilane and a hafnium alkoxide. From x-ray photoelectron spectroscopy, the deposited films are confirmed to be silicate with Hf–O–Si bonds but without any Hf–Si bonds. The permittivity calculated from the capacitance of the accumulation layer increases monotonically with an increase in the hafnium content, whereas the optical band gap energy estimated from vacuum ultraviolet absorption spectra decreases. Similar results were obtained from zirconium silicate films deposited using tetraethoxysilane and a zirconium alkoxide. If we compare the films with the same hafnium or zirconium content, the hafnium silicate exhibits a higher permittivity and a larger band gap energy than the zirconium silicate.