We report on the fabrication and characterization of a single-crystal diamond device for the electrical stimula- tion of light emission from nitrogen-vacancy (NV0) and other defect-related centers. Pairs of sub-superficial graphitic micro-electrodes
embedded in insulating diamond were fabricated by a 6 MeV C3+ micro-beam irra- diation followed by thermal annealing. A photoluminescence (PL) characterization evidenced a low radiation damage concentration in the inter-electrode gap region, which did not significantly affect the PL features domi- nated by NV centers. The operation of the device in electroluminescence (EL) regime was investigated by ap- plying a bias voltage at the graphitic electrodes, resulting in the injection of a high excitation current above a threshold voltage (~300V), which effectively stimulated an intense EL emission from NV0 centers. In addition, we report on the new observation of two additional sharp EL emission lines (at 563 nm and 580 nm) related to interstitial defects formed during MeV ion beam fabrication.
Focused MeV ion beams with micrometric resolution are suitable tools for the direct writing of conductive graphitic channels buried in an insulating diamond bulk. Their effectiveness has been shown for the fabrication of multi-electrode ionizing radi
ation detectors and cellular biosensors. In this work we investigate such fabrication method for the electrical excitation of color centers in diamond. Differently from optically-stimulated light emission from color centers in diamond, electroluminescence (EL) requires a high current flowing in the diamond subgap states between the electrodes. With this purpose, buried graphitic electrode pairs with a spacing of 10 $mu$m were fabricated in the bulk of a single-crystal diamond sample using a 6 MeV C microbeam. The electrical characterization of the structure showed a significant current above an effective voltage threshold of 150V, which was interpreted according to the theory of Space Charge Limited Current. The EL imaging allowed to identify the electroluminescent regions and the residual vacancy distribution associated with the fabrication technique. Measurements evidenced bright electroluminescent emission from native neutrally-charged nitrogen-vacancy centers ($NV^0$); the acquired spectra highlighted the absence of EL associated with radiation damage.
In multi-electrode detectors, the motion of excess carriers generated by ionizing radiation induces charge pulses at the electrodes, whose intensities and polarities depend on the geometrical, electrostatic and carriers transport properties of the de
vice. The resulting charge sharing effects may lead to bipolar currents, pulse height defects and anomalous polarity signals affecting the response of the device to ionizing radiation. This latter effect has recently attracted attention in commonly used detector materials, but different interpretations have been suggested, depending on the material, the geometry of the device and the nature of the ionizing radiation. In this letter, we report on the investigation in the formation of anomalous polarity pulses in a multi-electrode diamond detector with buried graphitic electrodes. In particular, we propose a purely electrostatic model based on the Shockley-Ramo-Gunn theory, providing a satisfactory description of anomalous pulses observed in charge collection efficiency maps measured by means of Ion Beam Induced Charge (IBIC) microscopy, and suitable for a general application in multi-electrode devices and detectors.
