A Review of the Simulation of Point Defects in KDP Crystals

Abstract

KDP crystal is a frequency-doubling material with excellent optical properties, but the large number of intrinsic defects and metal impurities in KDP crystal are the main reasons restricting its wide application. Based on first-principles, extensive and indepth studies have been conducted on various defects in KDP crystals. The calcaulated results indicate that H defects and O defects are the main intrinsic defects causing the decrease in the Laser-Induced Damage Threshold (LIDT) of KDP crystals. The coupling of Self-Trapped Holes (STHs) with these intrinsic defects as well as metal impurities also plays an important role in the LIDT reduction. When impurities such as Si and Ti are present in the crystal, STHs are localized on a single O ion; when impurities such as Al and Fe exist, STHs are localized on two O ions. For divalent metal ions (Ba, Mg, Ca) substituting for K ions, the +1 charged defect state is usually the most stable. For divalent metal ion clusters, the neutral defect state is the most stable. For example, Ba-substituted K defects can generate defect states near the valence band maximum (VBM) and conduction band minimum (CBM), thereby increasing the probability of multiphoton transitions. For trivalent metal ion (Al, Fe, Cr, La, Y) doping (including isolated defects and defect clusters), relatively strong defect states are generally generated in the band gap, and the lattice relaxation energy of multiphoton transitions is also generally larger. Meanwhile, the absorption spectra generated by trivalent ion defects show good agreement with experimental results. Therefore, compared with divalent metal impurities, trivalent impurities may play a more important role in crystal damage.