Three-dimensional graphite electrodes in CVD single crystal diamond detectors: Charge collection dependence on impinging β-particles geometry

The charge collection performance of a three-dimensional diamond-graphite detector is reported. Buried graphite pillars with high aspect ratio were formed inside a single crystal synthetic diamond slab by using a femtosecond IR laser with 200 kHz of repetition rate. Grouped in two series and connected by graphite strips on the surface, eight independent 3D electrodes were used to collect the charge carriers generated by energy deposited in the detector by 90Sr,Y β-particles. Different impinging configurations were used to test charge collection and signal dependence on voltage. Reversing the bias polarity the pulse height distribution does not changes and the charge collection saturation of any group of connected pillars was observed around ±80 V (0.53 V/μm). The average charge collected by one pillars row is Qav=1.60±0.02 fC, with electrons impinging orthogonally the rows, in such a way demonstrating full charge collection.