Gallium Arsenide particle detectors: a study of the active region and charge-collection efficiency

Gallium arsenide particle detectors made by Alenia SpA have been tested within the context of the RD-8 project and found to have a high charge-collection efficiency (75%). We have analysed the data and found the overall behaviour of these detectors to be coherent and understandable in terms of one function: the local charge-collection efficiency. Two ways have been used to measure the width of the active region and the increase of such a width as a function of bias is found not to be consistent with a simple square-root law.