Beomjun Park

Halide perovskite single crystals are promising active materials for direct x‐ray detectors because of their strong x‐ray absorption, efficient charge transport, and solution‐processable crystal growth. However, in thick single‐crystal detectors, lateral side surfaces can act as conductive leakage pathways, increasing dark current, inducing baseline drift, and generating transient overshoot and undershoot during x‐ray irradiation. Previous passivation and heterojunction strategies have mainly focused on metal–semiconductor interfaces, leaving side‐surface transport pathways insufficiently controlled. Here, a selective side‐surface ion‐exchange strategy is developed to construct halide‐gradient sidewall heterojunctions in MAPbBr ₃ single crystals. Through methylammonium chloride‐induced ion exchange, compositionally graded MAPbBr _{3 − x} Cl _x /MAPbBr ₃ multi‐heterojunctions are formed along the crystal sidewalls, creating wide‐bandgap lateral barriers that confine charge carriers within the Br‐rich bulk region. Spatial conductivity mapping and current‐distribution simulations reveal that the graded sidewalls suppress edge‐dominated conductivity and homogenize vertical charge transport without requiring guard‐ring electrodes. Consequently, side‐surface leakage, baseline drift, and transient undershoot are strongly suppressed, yielding reproducible and distortion‐free x‐ray responses. The treated detectors exhibit a 4.7‐fold enhancement in sensitivity, a 2.85‐fold reduction in detection limit, and markedly improved low‐dose x‐ray imaging contrast. This work establishes sidewall‐selective halide‐gradient engineering as a scalable route for lateral charge confinement in perovskite single‐crystal radiation detectors.

Radiation detectors operating in extreme environments such as nuclear accident sites, radioactive waste facilities, space missions, and post‐detonation scenarios must maintain reliable radionuclide identification under prolonged high‐dose irradiation. However, radiation‐induced defect accumulation progressively degrades spectroscopic performance, and the mechanisms governing reversible detector operation under extreme irradiation remain not fully understood. Here, we report a zero‐dimensional perovskite‐inspired Cs ₃ Cu ₂ I ₅ single‐crystal scintillator that exhibits fully reversible spectroscopic degradation under ultra‐high‐dose γ‐ray irradiation of ∼200 kGy. The radiation response was systematically investigated by correlating structural, optical, and spectroscopic analyses before and after mild thermal recovery. Structural and spectroscopic analyses reveal that irradiation induces predominantly interstitial‐type lattice disorder while preserving long‐range crystallinity and the intrinsic self‐trapped exciton emission framework. Despite reduced light output, the degraded spectroscopic performance is completely restored through mild thermal activation at 100°C without device refabrication. Under simultaneous six‐radionuclide γ‐ray fields, the scintillator maintains distinguishable spectral features and high post‐irradiation energy linearity (R ² = 0.9973), outperforming conventional NaI(Tl) under comparable conditions. These findings highlight defect‐mediated reversibility as a promising design strategy for radiation‐resilient scintillators operating in extreme environments.

CdTe‐based compound semiconductors, particularly CdZnTe(CZT), have shaped the technological foundation of room‐temperature gamma‐ray spectrometers through continuous advances in crystal growth, defect control, and device engineering. While metal halide perovskites have recently emerged as promising direct‐conversion materials for gamma‐ray spectroscopy, their performance is consistently evaluated in reference to CZT detectors, reflecting a deeper continuity in device physics and architecture rather than a simple comparison of material properties. This Review examines the parallel evolution of CdTe‐derived and metal halide perovskite gamma‐spectrometers and identifies the shared physical and device‐level principles that underpin high‐resolution spectroscopy. We revisit the historical development of CdTe‐based detectors, highlighting how bandgap engineering, defect suppression, surface passivation, and contact design enabled spectroscopic‐grade operation at room temperature, and analyze how analogous challenges are addressed in perovskite gamma‐spectrometers to achieve intrinsic electrical states, suppress dark current, mitigate defect‐related instabilities, and improve their spectral performance. Across both material platforms, particular emphasis is placed on geometrical device engineering for weighting‐potential control, which emerges as a decisive factor in realizing high energy resolution beyond intrinsic material metrics alone. By consolidating these developments, this Review elucidates a shared design heritage in gamma‐ray spectroscopy technology and provides a rational framework for the development of next‐generation semiconductor‐based gamma‐spectrometers.

MAPbBr ₃ single crystals (MPB SCs) are promising materials for X‐ray detection; however, their use in low‐dose imaging is limited by high dark current, low detectability, and noise that degrades image clarity. Under X‐ray irradiation, where electron–hole pair generation is inherently low, suppressing defects is critical to minimize losses and maximize charge collection. In this study, metastable zone engineering is employed by tuning the MABr:PbBr ₂ ratio during inverse temperature crystallization (ITC) to produce defect‐suppressed MPB SCs. Excess MABr broadens and stabilizes the metastable zone, reducing nucleation events and enabling the growth of large, high‐crystallinity MPB SCs exceeding 10 mm within 11 h. These crystals exhibit electronic properties closer to intrinsic behavior, with prolonged carrier lifetimes of 371 ns and an enhanced mobility‐lifetime ( µτ ) product of 3.43 × 10 ⁻³ cm ² V ⁻¹ . Photoluminescence spectra reveal a distinct secondary peak from photon recycling, with intensity 1.25 times greater than the band‐edge peak, indicating efficient photon reabsorption due to reduced non‐radiative losses. Devices fabricated from excess MPB SCs achieve a record‐low detection limit of 0.47 nGy s ⁻¹ , high sensitivity (6.117 × 10 ³ µC Gy _air ⁻¹ cm ⁻² ), and high‐resolution X‐ray imaging, demonstrating strong potential for advanced medical and industrial applications.