Use of the drift-time method to measure the electron lifetime in long-drift-length CdZnTe detectors.

The traditional method for electron lifetime measurements of CdZnTe (CZT) detectors relies on using the Hecht equation. The procedure involves measuring the dependence of the detector response on the applied bias to evaluate the μτ product, which in turn can be converted into the carrier lifetime. Despite general acceptance of this technique, which is very convenient for comparative testing of different CZT materials, the assumption of a constant electric field inside a detector is unjustified. In the Hecht equation, this assumption means that the drift time would be a linear function of the distance. This condition is not fulfilled in practice at low applied biases, where the Hecht equation is most sensitive to the μs product. As a result, researchers usually take measurements at relatively high biases, which work well in the case of the low μτ-product material, <10-3 cm²/V, but give significantly underestimated values for the case of high μτ-product crystals. In this work, we applied the drift-time method to measure the electron lifetimes in long-drift-length (4 cm) standard-grade CZT detectors produced by the Redlen Technologies. We found that the electron μτ product of tested crystals is in the range 0.1-0.2 cm²/V, which is an order of the magnitude higher than any value previously reported for a CZT material. In comparison, using the Hecht equation fitting, we obtained μτ=2.3 × 10-2 cm²/V for a 2-mm thin planar detector fabricated from the same CZT material. [ABSTRACT FROM AUTHOR]