Abundant Shallow Traps in FAPbBr ₃ Single Crystal γ-Ray Detectors

Formamidinium lead bromide (FAPbBr 3 ) perovskite single crystals are promising candidates for room temperature γ-ray spectroscopy, where deep trap densities have been suppressed to 10 10 cm –3 to minimize carrier recombination. However, the abundant shallow traps intrinsic to perovskites continue to govern charge transport dynamics, while their density, spatial distribution, and impact on detector performance remain poorly understood in Formamidinium lead bromide single crystal γ-ray detectors. Here, we quantitatively investigate shallow traps in Formamidinium lead bromide single crystal γ-ray detectors by resolving trap mediated charge transport under monoenergetic 57 Co single photon excitation. The charge sensitive preamplifier output reveals a distinct two stage charge transition arising from recursive trapping–detrapping processes. We show that approximately 15% of photogenerated carriers are temporarily trapped and re-emitted, and these shallow states contribute ∼86% of the total charge collection time. Depth resolved analysis using cathode to anode signal ratios in pixelated detectors further uncovers a pronounced surface enriched distribution of shallow traps. And blue light soaking effectively fills surface shallow states, leading to markedly improved charge collection efficiency and energy resolution. These results establish surface dominated shallow traps as the primary transport bottleneck in perovskite radiation detectors and provide guidance for defect engineering strategies toward high resolution room temperature γ-ray spectroscopy.