Al2O3 Coating as Passivation Layer for CZT-based Detectors

CdZnTe is nowadays a reference semiconductor for detection of X and ?-radiation. The electrical properties of CdZnTe-based (CZT) detectors are strongly affected by the surface and subsurface defects, which can cause an excessive surface leakage current (SLC). This issue strongly degrades the sensor performance and becomes critical for multi-stripes detectors, where the stripes are kept at different voltage potentials in order to shape the electric field inside the semiconductor material.In this work, we propose a passivation method based on the deposition of a thin AlO film on the non-metallized CZT surface. To demonstrate the effectiveness of the method, we fabricated several 19.4x19.4x5 mm CZT multi-stripes detectors with 48 parallel Au stripes on the anode face (12 collecting anodes and 36 drift stripes) and subsequently deposited a AlO polycrystalline thin film on the CZT surface between the stripes. AlO deposition was achieved by sputtering technique. Electrical characterization of surface leakage current before and after AlO is presented.AlO coating treatment allowed us to obtain exceptionally low surface leakage current values, 10 to 100 times lower than those measured after our best wet passivation method for CZT surface chemical oxidation. Since AlO passivation significantly reduces surface leakage current and thus improves the signal-to-noise ratio, our finding is very promising for a substantial advancement of multi-stripe detectors performance.