The role of charge trapping at grain boundaries on charge transport in polycrystalline chemical vapor deposited diamond based detectors

摘要

We report a detailed investigation of the trapping and release of charge carriers from grain boundaries in polycrystalline diamond grown by chemical vapor deposition (poly-CVD). A model for charge trapping and release is presented for samples which display very different bulk characteristics as determined by photolummescence, dark conductivity, and thermally stimulated current measurements. Experimental studies were performed as a function of temperature and applied electric field using ion beam induced charge to map the charge collection efficiency of charge induced by a scanned, focused, 2 MeV He~+ microprobe. Even though the carrier velocity and charge collection efficiency should begin to saturate at electric fields above 1 x 10~4 V/cm, the efficiency was found to increase by a factor of 3 when the electric field is increased to greater than 1 x 10~5 V/cm. A model based on the localized enhancement of the electric field caused by trapped charge at grain boundaries is found to account for this unexpected result. Further, we find that this localized variation in electric field strongly affects charge transport in poly-CVD diamond and is therefore an important consideration for optimizing detector performance.