3D imaging of radiation damage in silicon sensor and spatial mapping of charge collection efficiency

Radiation damage in semiconductor sensors alters the response and degrades the performance of many devices ultimately limiting their stability and lifetime. In semiconductor radiation detectors the homogeneity of charge collection becomes distorted while decreasing the overall detection efficiency. Moreover the damage can significantly increase the detector noise and degrade other electrical properties such as leakage current. In this work we present a novel method for 3D mapping of the semiconductor radiation sensor volume allowing displaying the three dimensional distribution of detector properties such as charge collection efficiency and charge diffusion rate. This technique can visualize the spatially localized changes of local detector performance after radiation damage. Sensors used were 300 μm and 1000 μm thick silicon bump-bonded to a Timepix readout chip which serves as an imaging multichannel microprobe (256 × 256 square pixels with pitch of 55 μm, i.e. all together 65 thousand channels). Per pixel energy sensitivity of the Timepix chip allows to evaluate the local charge collection efficiency and also the charge diffusion rate. In this work we implement an X-ray line scanning technique for systematic evaluation of changes in the performance of a silicon sensor intentionally damaged by energetic protons.