Characteristics of irradiated silicon microstrip detectors with <100> and <111> substrates

In a program of developing radiation-hard silicon sensors for the LHC-ATLAS experiment, we have irradiated various types of silicon sensors with 12 CeV protons at KEK. Among the other properties, we made a comparative study of characteristics of the sensors with two wafer planes <111> and <100>. The studied sensors are p-on-n type, which satisfy the ATLAS-SCT specifications. Possible dependence on the substrate orientation could result from different dangling-bond configurations. The compared characteristics are the charge collection efficiency, interstrip capacitance, and noise levels. The noise levels were measured with a real ATLAS-SCT electronics system. A substantial difference is observed in the interstrip capacitance at ~10 kHz, while the difference is small at >1 MHz. The differences in the charge collection efficiency and in the noise levels appear to be small. (5 refs).