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

• Published in: IEEE sensors journal 2019-12, Vol.19 (24), p.11908-11917
• Main Authors: Salvatori, Stefano, Jaksic, M., Rossi, Maria Cristina, Conte, Gennaro, Kononenko, Taras, Komlenok, Maxim, Khomich, Andrey, Ralchenko, Victor, Konov, Vitaly, Provatas, G.
• Format: Article
• Language: English
• Subjects: 3D detectors; Anisotropy; Charge efficiency; Collection; Columns (structural); Crystal defects; Crystals; Dark current; Detectors; Diamond; Diamonds; Efficiency; Electric contacts; Electric field strength; Electrodes; graphitic pillars; Graphitization; IBIC; Ion beams; Laser beams; Lasers; Mapping; Micrometers; Optical microscopy; Polarizers; protons; Raman spectroscopy; sc-CVD diamond; Sensors; Single crystals; Stress; Strips; Strontium 90; β-particles
• ISSN: 1530-437X; 1558-1748
• DOI: 10.1109/JSEN.2019.2939618

The paper reports the micron-scale investigation of an all-carbon detector based on synthetic single crystal CVD-diamond having an array of cylindrical graphitic buried-contacts, about 20μ m in diameter each, connected at the front side by superficial graphitic strips. To induce diamond-to-graphite transformation on both detector surface and bulk volume, direct-laser-writing technique was used. Laser-treatment parameters and cell shape have been chosen to minimize the overlapping of laser-induced stressed volumes. Optical microscopy with crossed polarizers highlighted the presence of an optical anisotropy of the treated material surrounding the embedded graphitized columns, and non-uniform stress in the buried zones being confirmed with a confocal Raman spectroscopy mapping. Dark current-voltage characterization highlights the presence of a field-assisted detrapping transport mainly related to highly-stresses regions surrounding buried columns, as well as superficial graphitized strips edges, where electric field strength is more intense, too. Notwithstanding the strain and electronic-active defects, the detector demonstrated a good charge collection produced by 3.0 and 4.5 MeV protons impinging the diamond, as well as those generated by MeV β-particles emitted by 90 Sr source. Indeed, the mapping of charge collection efficiency with Ion Beam Induced Charge technique displayed that only a few micrometers thick radial region surrounding graphitic electrodes has a reduced efficiency, while most of the device volume preserves good detection properties with a charge collection efficiency around 90% at 60 V of biasing. Moreover, a charge collection efficiency of 96% was estimated under MeV electrons irradiation, indicating the good detection activity along the buried columns depth.