Influence of Defect Al Substituting for P on Tunneling Effect and Self‐Trapped Hole in KH ₂ PO ₄ Crystal

Based on the first principles, research is carried out on one of the main impurities in the KDP (KH 2 PO 4 ) crystal: Al. Since the existence form of aluminum impurities in the crystal has not been determined experimentally, it is assumed that it exists in the form of the defect aluminum substituting for phosphorus (Al P ). Through research, it has been found that the defect exists in the crystal in a −2 charged state (Al P 2′ ) when Fermi level is greater than 4 eV, it becomes the −3 charged defect state (Al P 3′ ). Due to lattice distortion, the collapse of the quantum tunneling effect of H ions caused by it is transmissible within the crystal. At the same time, because it captures H ions to compensate for its own charge, it leads to the loss of positive charges of the phosphate groups within the supercell, which makes it easier to generate Defect B (H 2 PO 4 , a self‐trapped hole captured by the dihydrogen phosphate group) in the crystal. When the crystal is irradiated by a laser, this phenomenon will be more likely to occur.