Buried graphite electrodes in single crystal CVD Diamond investigated with MeV protons and electrons

The paper reports the study of an asymmetric detector with graphite contacts, about 20 µ m in diameter, buried within a synthetic single crystal diamond. To induce diamond-to-graphite transformation a femtosecond IR laser is used on the surface and bulk volume. Optical microscopy with crossed polarizers has evidenced optical anisotropy laterally the buried pillared contacts whereas the regions between pillars exhibited the presence of both tensile and compressive stress there around, as revealed with Raman spectroscopy mapping. Notwithstanding the strain, the buried electrodes showed linear electrical response and demonstrated ability to collect the charge carriers produced by 3.0 and 4.5 MeV protons as well as MeV electrons emitted by 90Sr. The charge collection efficiency (CCE) dependence on voltage evaluated using 4.5 MeV protons in the ±100 V range saturates at around 92±2% at 100 V, while coincidence experiments with MeV electrons confirmed that the whole pillars length is active in collecting the charge carriers. The mapping of CCE spatial distribution with an ion beam induced current technique showed that only a narrow (a few microns) damaged zone around the graphite electrodes has a reduced CCE, while the main diamond volume preserves excellent detection properties.