CdTe and CdZnTe detectors for timing measurements

We report the timing properties of CdTe and CdZnTe detectors in planar configuration. By utilizing ²⁴¹Am doped scintilator, we have developed a new method to evaluate the timing performance of the semiconductor detector. We confirm that the slow mobility and short life time of holes significantly degrades the timing performance. To achieve high carrier speed, either by applying a high electric field or by selecting only electrons, is very important for obtaining a detector with fast, ∼ nsec timing capability. To select only the electron events, we adopt the pulse height selection with a fast-slow shaping amplifier. In conjunction with a newly developed CdTe diode, we obtain a superior performance of 5.8 nsec. We also discuss the application for Positron Emission Tomography with 511 keV gamma-gamma coincidence method, and found that a geometrical arrangement in which electrodes are parallel to the incident γ-rays gives about 3 time better timing response than is available when the electrodes are perpendicular to the γ-ray beam.