Diamond Detector With Laser-Formed Buried Graphitic Electrodes: Micron-Scale Mapping of Stress and Charge Collection Efficiency

The paper reports the micron-scale investigation1 of an all-carbon detector based on synthetic single crystal2 CVD-diamond having an array of cylindrical graphitic buried-3 contacts, about 20 µm in diameter each, connected at the4 front side by superficial graphitic strips. To induce diamond-5 to-graphite transformation on both detector surface and bulk6 volume, direct-laser-writing technique was used. Laser-treatment7 parameters and cell shape have been chosen to minimize the over-8 lapping of laser-induced stressed volumes. Optical microscopy9 with crossed polarizers highlighted the presence of an optical10 anisotropy of the treated material surrounding the embedded11 graphitized columns, and non-uniform stress in the buried12 zones being confirmed with a confocal Raman spectroscopy13 mapping. Dark current-voltage characterization highlights the14 presence of a field-assisted detrapping transport mainly related15 to highly-stresses regions surrounding buried columns, as well as16 superficial graphitized strips edges, where electric field strength17 is more intense, too. Notwithstanding the strain and electronic-18 active defects, the detector demonstrated a good charge collection19 produced by 3.0 and 4.5 MeV protons impinging the diamond,20 as well as those generated by MeV β-particles emitted by 90Sr21 source. Indeed, the mapping of charge collection efficiency with22 Ion Beam Induced Charge technique displayed that only a few23 micrometers thick radial region surrounding graphitic electrodes24 has a reduced efficiency, while most of the device volume25 preserves good detection properties with a charge collection26 efficiency around 90% at 60 V of biasing. Moreover, a charge27 collection efficiency of 96% was estimated under MeV electrons28 irradiation, indicatingthe good detection activity along theburied29 columns depth