纤锌矿Zn1-xMgxO合金相结构稳定性的第一性原理研究

采用基于密度泛函理论中局域密度近似下的VASP程序包,在考虑所有掺杂构型前提下,对Zn1-xMgxO合金的晶格参数、禁带宽度以及形成焓随Mg含量的变化进行了系统地计算.计算结果表明：随着Mg含量的不断增加,纤锌矿Zn1xMgxO合金的平均晶格常数变化不遵循Vergard定律;合金的禁带宽度随着Mg含量增加满足二次函数关系Eg=3.43＋2.24x＋0.68x2,与实验结果一致,不同掺杂原子构型禁带宽度的差异是纤锌矿Zn1-xMgxO合金中发光光谱宽化的重要原因;对比分析纤锌矿、闪锌矿和熔岩矿三种相结构的Zn1-xMgxO合金形成焓的计算结果发现,当Mg掺杂比例为37.5%时,Zn1-xMgxO合金由纤锌矿向熔岩矿结构转变;闪锌矿Zn1-xMgxO合金形成焓始终低于纤锌矿,在特殊的条件下,可以形成闪锌矿Zn1-xMgxO合金相.

First principles study the phase structure stability of wurtzite Zn1-xMgxO alloy

The VASP （Vienna Ab-initio Simulation Package） that based on the density-functional theory （DFT） method combined with local density approximation （LDA） is used to calculate the lattice parameters, band gap, and formation enthalpy of Zn1-xMgxO alloy taking all the doping configurations into account. The calculation results indicate that the average parameters of wurtzite （wz） Zn1-xMgxO alloy, a and c, don’t follow the Vergard’s law. With increasing the Mg content, the band gap is increased and the variation of band gap can be fitted by Eg=3.43＋2.24x＋0.68x2, which is in agreement with the experimental results. The difference of Eg values in different doping configurations is the main reasons to widen the photoluminescence spectra of Zn1-xMgxO alloy. By comparing the formation enthalpy of wurtzite Zn1-xMgxO with those of zinc blende and rocksalt Zn1-xMgxO alloys, we find that the Zn1-xMgxO alloy will transit from wurtzite phase into rocksalt beyond x=37.5% and wurtzite Zn1-xMgxO phase can be coexistence with that phase of zinc blende Zn1-xMgxO alloys at special growth condition.