ZnO中Li相关缺陷结构性质

采用第一性原理量子力学分子动力学方法,基于32个原子的超原胞模型,计算了ZnO中各种Li相关缺陷的有关几何和电子结构。通过不同模型的计算分析表明,ZnO中Li杂质在间隙位上的总能比替位Zn格位的能量更低,但却形成施主能级。进一步通过构造Li替Zn位Li_Zn与不同本征缺陷所构成的复合体结构,并对模拟计算的结果进行分析比较得出,O反位O_Zn可与Li_Zn形成比Li间隙位更稳定的复合体,可高溶解度地稳定存在于ZnO中,并在禁带中产生受主能级,是较好的p型导电性候选缺陷。

Structure Properties of Li-related Defects in ZnO

Considerable attention has been paid to ZnO due to its wide direct band gap of 3.3 eV and large(exciton) binding energy of 60 meV at room temperature.Thus it becomes a promising material for ultraviolet light emitting diodes and lasers, transparent high power electronic devices and widely used in our community.In order to fabricate ZnO-based optoelectronic devices,both n-and p-type ZnO are needed.Undoped ZnO(exhibits) intrinsic n-type conductivity,and it is,therefore,difficult to achieve p-type ZnO because the fact that acceptors are compensated by various native donors,such as oxygen vacancies,Zn interstitial,and other(donors.) Except for the group-ⅴ dopants,Li is considered to be a shallow p-type impurity for ZnO.However,in practice it is still difficult to obtain p-type ZnO by Li dopant because Li substituting for Zn(Li_Zn) is metastable.Thus much attention has been paid on stability researches of p-type dopant in Li doped ZnO.The first-principles calculations were carried out with a powerful package called VASP(Vienna ab initio simulation package).The wave functions are expressed by plane waves with a cutoff energy 395.99 eV.Ionic potentials are represented by ultrasoft pseudopotentials with the Perdew-Wang 1991(PW91) GGA(genera-(lized) gradient approximation) correction.And 32-atom supercells were used to perform the total energy calcu-(lation.) Further,in order to improve the stability of Li_Zn in ZnO crystal,the geometrical and electronic structures of the different complexes of Li_Zn with native point defects were constructed and calculated.The calculated results show that some complexes of Li_Zn with native point defects can not only improve the stability and solubility of the defects,but also change their electronic structures.By comparing the stabilities and the related energy states of the complexes,O_Zn-Li_Zn complex has the lowest formation energy and also has shallow accept levels.It is suggested to be the best acceptor candidate for the p-type ZnO.But the formation of O_Zn-Li_Zn complex in practice is waiting for further investigations on crystal growth and device fabrication.