Disorder effects on the band structure of ZnGeN 2 : Role of exchange defects
Disorder effects on the band structure of ZnGeN 2 : Role of exchange defects
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无序对 ZnGeN 2 能带结构的影响：交换缺陷的作用
DOI：
10.1103/physrevb.94.205201
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发表时间：
2016
影响因子：
3.7
通讯作者：
W. Lambrecht
中科院分区：
文献类型：
--
作者：
Dmitry Skachkov;P. Quayle;K. Kash;W. Lambrecht
研究了交换缺陷对${\ mathm {ZnGeN}}_{2}$能带结构的影响。从理想的$Pna{2}_{1}$晶体结构出发，遵循局部八隅体规则，通过Zn和Ge阳离子的交换来定义交换缺陷。每次这样的交换都会产生几个以氮为中心的四面体，这些四面体违反了局部八隅体规则，尽管总体上保持了电荷中性。我们研究了交换缺陷的几种分布，其中一些是交换缺陷的所有对位彼此靠近，并且交换缺陷的数量越来越多，另一些是交换缺陷的两种对位${\ mathm {Zn}}_{\ mathm {Ge}}$和${\ mathm {Ge}}_{\ mathm {Zn}}$彼此分开。我们还比较了Zn和Ge在阳离子上完全随机分布的模型的结果。我们发现，对于单近邻交换缺陷，由于两种作用，带隙缩小了约0.5 eV:(1) ${\mathrm{Zn}}_{\mathrm{Ge}}}}$对位形成正好在上面的充满受体态，并与完美晶体${\mathrm{ZnGeN}}_{2}$的价带最大值（VBM）合并；(2)${\mathrm{Ge}}_{\mathrm{Zn}}$对位在导带形成共振，降低了导带最小值（CBM）。当产生更多的交换缺陷时，这些受体状态扩大成能带，可以进一步降低间隙。当四面体完全被四个Zn原子包围时，发现间隙中更深的态都定位在这些四面体附近，形成一个单独的中间带。最后，对于相分离的${\mathrm{Zn}}_{\mathrm{Ge}}$和${\mathrm{Ge}}_{\mathrm{Zn}}$，间隙明显减小，但没有发现分离带的出现。${\mathrm{Zn}}_{\mathrm{Ge}}$类受体态现在形成了一个明显更宽的渗透缺陷带，从而深入到间隙中。在所有情况下，新VBM顶部附近的波函数在一定程度上保持在${\mathrm{Zn}}_{\mathrm{Ge}}$附近。对于完全随机的情况，差距甚至更严重地减少了近3ev。体系总能量随着违反八隅体规则的四面体数量的增加而增加，每2ev级交换缺陷的能量成本相当高。
The role of exchange defects on the band structure of ${\mathrm{ZnGeN}}_{2}$ is investigated. Exchange defects are defined through the exchange of cations Zn and Ge starting from the ideal $Pna{2}_{1}$ crystal structure, which obeys the local octet rule. Each such exchange creates several nitrogen-centered tetrahedra which violate the local octet rule, although overall charge neutrality is preserved. We study several distributions of exchange defects, some with all antisites making up the exchange defect close to each other and with increasing numbers of exchange defects, and others where the two types of antisites ${\mathrm{Zn}}_{\mathrm{Ge}}$ and ${\mathrm{Ge}}_{\mathrm{Zn}}$ are kept separated from each other. We also compare the results for these models with a fully random distribution of Zn and Ge on the cation sites. We show that for a single-nearest-neighbor exchange defect, the band gap is narrowed by about 0.5 eV due to two effects: (1) the ${\mathrm{Zn}}_{\mathrm{Ge}}$ antisites form filled acceptor states just above and merging with the valence-band maximum (VBM) of perfect crystal ${\mathrm{ZnGeN}}_{2}$ and (2) the ${\mathrm{Ge}}_{\mathrm{Zn}}$ antisites form a resonance in the conduction band which lowers the conduction-band minimum (CBM). When more exchange defects are created, these acceptor states broaden into bands which can lower the gap further. When tetrahedra occur surrounded completely by four Zn atoms, states even deeper in the gap are found localized all near these tetrahedra, forming a separate intermediate band. Finally, for phase-segregated ${\mathrm{Zn}}_{\mathrm{Ge}}$ and ${\mathrm{Ge}}_{\mathrm{Zn}}$, the gap is significantly more reduced, but no separate band is found to occur. The ${\mathrm{Zn}}_{\mathrm{Ge}}$ acceptorlike states now form a percolating defect band which is significantly wider and hence reaches deeper into the gap. In all cases, the wave functions near the top of the new VBM remain, to some extent, localized near the ${\mathrm{Zn}}_{\mathrm{Ge}}$ sites. For a fully random case, the gap is even more severely reduced by almost 3 eV. The total energy of the system increases with the number of octet-rule-violating tetrahedra and the energy cost per exchange defect of order 2 eV is quite high.