Eu³⁺-induced passivation and charge-transport modulation in Cs₂FeCl₅·H₂O single crystals and evaporated thin films...

In recent years, metal halide compounds have been widely studied as a class of semiconductor materials with superior optoelectronic characteristics. In particular, rare metal doping has been observed to affect the properties of metal halide compounds, yet the mechanisms are not understood. In this study, we incorporated Eu³⁺ into the Cs₂FeCl₅·H₂O crystal system, aiming to thoroughly investigate its comprehensive effects on the material's structural, optical, and electrical properties, and ultimate performance as a photodetector. The results indicate that both the Cs₂FeCl₅·H₂O and Eu doping Cs₂FeCl₅·H₂O single crystals belong to the orthorhombic crystal system with the space group Cmcm (No. 63). The Eu³⁺ ion is successfully incorporated into the host lattice, which results in the lattice expansion phenomenon observed in X-ray diffraction (XRD), bandgap widening, increasing the resistance and emission intensity of the samples in photoluminescence. This positive outcome is attributed to the effective passivation realized by Eu³⁺ incorporation. The dark current density of the photodetector devices based on the Eu³⁺-doping decreased significantly from the undoped value of 18.3 ± 3.0 to 2.1 ± 1.2 µA cm^-2. Smaller dark current and high bulk resistance can effectively prevent semiconductor devices from breakdown, making them applicable in the field of high-power semiconductors. This work offers insight for the future design and development of metal halide photoelectronic materials with low noise and high response speed.