Proximity Charge Sensing With Semiconductor Detectors

Semiconductor radiation detectors are routinely used for the detection, imaging, and spectroscopy of gamma-ray, x-ray, and charged particles. In basic form, a detector is comprised of a semiconductor crystal with two or more electrodes formed on its surfaces. Besides allowing for the application of bias voltage, one or more of the electrodes on a detector also serve as readout electrode. Charge carriers drifting across the detector induce a charge signal on the electrode, which can then be measured by a charge-sensitive amplifier connected to the electrode. Although in general the readout electrodes of a detector are formed on the detector itself, charge can be induced on any electrode, even if the electrode is not physically in contact with the semiconductor. Such proximity charge sensing effects can be utilized to achieve a variety of advantages in applications involving semiconductor detectors. In this paper, we report on the experimental verification of signal readout using proximity electrodes and demonstrate several possible applications of this technique, including the position-sensitive readout of detectors and the sensing of incomplete charge collection in detectors as a means to reduce spectral background.