6N-Purity Germanium Detectors for α -Particle Spectroscopy via a-Ge:H/Al 2 O 3 Dual Passivation

High-purity germanium detectors (impurity concentration ≤1010cm-3) are widely used in precision radiation detection due to their extremely low noise and excellent energy resolution. However, their complex fabrication processes and high cost severely limit large-scale applications. To address this, we have developed a detector based on an a-Ge:H/Al2O3 dual passivation layer, which adopts a low-cost 6N germanium substrate with a doping concentration of 1012cm-3and a thickness of 500 μm, featuring a 5 × 5 mm2 active region surrounded by the guard rings, aiming to break through the technical bottleneck that low-purity germanium struggles to achieve efficient radiation detection by suppressing surface and contact defects. At 90 K, the detector interface state density is significantly reduced from 2.8×1012eV-1cm-2to 3.6×1011eV-1cm-2, and the reverse leakage current (@50 V) is drastically decreased from approximately 200 pA to 20 pA. The detector with the a-Ge:H/Al2O3dual passivation layer achieves an energy resolution of 376 keV (6.85%) under for241Am source (5.486 MeV), exhibiting a well-defined spectrum peak. In contrast, the detector without this dual passivation layer shows no distinct peak. This study lays a foundation for the application of low-purity germanium in portable radiation monitoring and integrated detection arrays, and provides key passivation technology support for the development of thick detectors.