Refined Synthesis and Single Crystal Growth of PbGa₂Se₄ by Chemical Vapor Transport Method for Photodetection

Ternary chalcogenide PbGa₂Se₄ with high resistivity, photosensitivity, and excellent nonlinear properties, exhibits a potential application in optoelectronic and nonlinear optical devices. However, the preparation of large-sized pure PbGa₂Se₄ crystals is challenging due to the presence of peritectic reaction (Formula presented.) and a narrow homogeneity region. Here, a “quenching-annealing” method (quenching at 850 °C in ice water, and then annealing at 650 °C for 250 h by reheating) is developed to eliminate the PbSe second phase during the synthesis. Subsequently, the PbGa₂Se₄ single crystals are successfully grown using chemical vapor transport (CVT) with the I₂ as the transport agent. The resulting crystal exhibits the crystal structure belonging to Fddd space group with the lattice parameters of a = 12.7192 Å, b = 21.2831 Å, and c = 21.5226 Å. Additionally, it possesses a wide bandgap (≈2.26 eV), high resistivity (6.59 × 10¹² Ω·cm), and defect density calculated via space charge limited current measurement (SCLC) as 2.46 × 10¹¹ cm⁻³. Photodetectors based on these as-grown crystals demonstrate exceptional photosensitivity along with a high detectivity (3.2 × 10⁸ Jones).