Charge Collection Efficiency of ALICE Silicon Drift Detectors

The charge collection efficiency (CCE) is an important characteristic of the overall detector quality. And as such, the CCE is a good parameter to control detector production process. The ALICE silicon drift detectors are going to be used for particle identification providing specific ionization loss, dE/dx, measurements. The knowledge of CCE is important to achieve precision in dE/dx measurements. Impurities presented in Si bulk of silicon drift detectors could trap drifting charge carriers. This results in the dependence of the charge collected on the anode on the carriers drift time. The Shockley-Read-Hall recombination-generation model is used to analyze the charge loss phenomena. The CCE data were obtained during laser testing of small "baby" detectors and accepted ALICE silicon drift detectors. Results and discussion of the CCE measurements are presented.