Insight into the damage mechanism of KH2PO4 crystals with BaK-SiP by hybrid density functional theory

Abstract

The laser-induced damage threshold (LIDT) of potassium dihydrogen phosphate (KDP) crystals is one of the key factors affecting the application of KDP crystals for Inertial confinement fusion (ICF). Previous studies have found that Ba, Si impurities can form BaK-SiP defect complexes in KDP crystals. However, the microscopic nature of the defect complexes is still unclear. We precisely calculate defect formation energy (DFE) in various charge states (-1, 0, +1), configuration coordinate diagram (CCD) and optical spectra by hybrid density functional theory. We found BaK-SiP introduce two defect states in the band gap. In the transitions (BaK-SiP)✕+h∙→(BaK-SiP)∙ and (BaK-SiP)✕+e-→(BaK-SiP)′, excited state and ground state have an intersection point in the Marcus inverted region and the activation energies are nearly 0 eV. The results showed that the defect complexes could capture holes and electrons through lattice relaxation, causing significant heat deposition and resulting in crystal damage. This implies a new damage mechanism of KDP crystals is discovered.