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采用第一性原理方法计算了KH2PO4(KDP)晶体中各种荷电态的硫取代磷替位缺陷(SP)的几何驰豫构型及电子结构.讨论了该缺陷形成后电荷密度的重新分布、相应的电子态密度、能带结构等性质.主要结果为:虽然中性态、±1以及+2荷电态的Sp替位缺陷并没有在带隙中形成占据态,但它们削弱了SO4基团与周围原子的结合力,从而形成相对孤立的SO4基团,相对于无缺陷晶体而言,这种局域松散的结构有利于杂质原子的填隙,因而会间接地影响该材料的抗激光损伤能力.-2荷电态的Sp替位缺陷则在带隙中形成能够容纳4个电子的未占据态,使KDP晶体的带隙大大降低,提高了光吸收能力,降低了激光损伤阈值,同时该荷电态导致SO4四面体畸变严重,甚至使得周围的两个O—H键断裂,从而造成微结构的几何损伤.以上结果清楚地阐明了硫酸根影响KDP激光损伤阈值的微观物理背景.
The geometrical relaxation structures and electronic structures of sulfur-substituted phosphorus substitution defects (SPs) for various charge states in KH2PO4 (KDP) crystals were calculated by the first-principles method. The redistribution of charge density after the formation of defects , The corresponding electronic density of states, the structure of the band structure, etc. The main results are as follows: although the neutral states, the Sp substations at ± 1 and +2 charge states do not occupy the band gap, they weaken the SO 4 Group with the surrounding atoms to form a relatively isolated SO4 group. This loosely localized structure favors the interstitialization of impurity atoms relative to defect-free crystals and thus indirectly affects the material’s resistance Laser damage ability.-2 Charged Sp substitutional defects form an unoccupied state in the bandgap that can accommodate four electrons, greatly reducing the bandgap of KDP crystals, increasing the light absorption capacity, and reducing the laser damage threshold , And at the same time, the charge state leads to serious tetrahedral distortion of SO 4 and even fracture of the two O-H bonds in the periphery, resulting in geometric damage of the microstructure.The above results clearly illustrate the microscopic physical background of sulfate radical affecting KDP laser damage threshold .