IBIC imaging of intra-crystallite charge transport in CVD diamond at reduced temperature

Abstract

We present high resolution maps of charge collection efficiency in polycrystalline CVD diamond film, acquired using ion beam induced charge imaging with a 2 MeV He 2+ microbeam. By measuring the charge collection efficiency in a coplanar electrode device, it is possible to observe the spatial variations in charge drift length within a single large-area diamond crystallite. The measured charge collection efficiency within the crystallite increases with bias voltage, with no saturation observed at voltages up to −250 V, corresponding to an average bulk electric field of 2.5 V/μm. When cooling the device from 297 K to 200 K, the maximum charge collection efficiency decreases from 70% to 13% due to a reduction in charge carrier lifetime. This data gives an insight into the role of relatively shallow traps present within diamond crystallites, which tend to limit the charge drift length in CVD diamond radiation detectors at room temperature.