论文标题
在绝缘晶体中控制掺杂剂的电荷状态：掺杂蓝宝石的案例研究
Control of charge state of dopants in insulating crystals: Case study of Ti-doped sapphire
论文作者
论文摘要
我们研究了电荷状态控制的机制和掺杂的绝缘晶体中不同点缺陷的浓度。该方法基于密度功能理论的计算。我们将其应用于获得高标准（FOM）的Ti掺杂蓝宝石晶体的问题。给定样品的FOM定义为在泵频率下吸收系数与在Ti：Sapphire Laser的工作频率下吸收系数的比率。据认为，FOM与隔离的Ti $^{3+} $ ions与Ti $^{3+} $ -Ti $^{4+} $ Pairs的浓度的浓度成正比。我们发现，通常，该比率与Ti $^{4+} $隔离的替代缺陷的浓度成正比，其比例系数取决于达到缺陷的热力学平衡浓度的温度。我们认为，在某些情况下，可能会违反Ti $^{3+} $ -Ti $^{4+} $和Ti $^{4+} $的浓度之间的反比例。我们表明，带电缺陷的积极形成的代码剂可能会降低（增加）主掺杂剂形成的正电荷缺陷的浓度。为了评估编码的效果，重要的是要考虑不仅孤立的缺陷，而且要考虑由代码群形成的缺陷复合物。特别是，我们表明，ti：蓝宝石与氮的编码会导致Ti $^{4+} $的浓度的必不可少，并且在氮或氮的降低中，在存在氮或其化合物的情况下，生长或退火是对产生Ti：Sapphire Laser Cyreser的化合物。开发的方法可用于确定具有所需特征的掺杂晶体的适当生长和退火条件。
We study mechanisms of control of charge state and concentration of different point defects in doped insulating crystals. The approach is based on the density functional theory calculations. We apply it to the problem of obtaining of Ti-doped sapphire crystals with high figure-of-merit (FOM). The FOM of a given sample is defined as the ratio of the coefficient of absorption at the pump frequency to the coefficient of absorption at the working frequency of Ti:sapphire laser. It is believed that FOM is proportional to the ratio of the concentration of isolated Ti$^{3+}$ ions to the concentration of Ti$^{3+}$-Ti$^{4+}$ pairs. We find that generally this ratio is in inverse proportion to the concentration of Ti$^{4+}$ isolated substitutional defects with the coefficient of proportionality that depends on the temperature at which the thermodynamically equilibrium concentration of defects is reached. We argue that in certain cases the inverse proportion between concentrations of Ti$^{3+}$-Ti$^{4+}$ and Ti$^{4+}$ may be violated. We show that codopants that form positively (negatively) charged defects may decrease (increase) the concentration of positively charged defects formed by the main dopants. To evaluate the effect of codoping it is important to take into account not only isolated defects but defect complexes formed by codopants, as well. In particular, we show that codoping of Ti:sapphire with nitrogen results in an essential increase of the concentration of Ti$^{4+}$ and in a decrease of the FOM, and, consequently, growth or annealing in the presence of nitrogen or its compounds is unfavorable for producing Ti:sapphire laser crystals. The approach developed can be used for determining appropriate growth and annealing conditions for obtaining doped crystals with the required characteristics.
