介稳岩盐ZnO为$p$型可掺杂型
Metastable rocksalt ZnO is $p$-type dopable
摘要：
尽管几十年的努力，实现$p$型导电性的宽带隙ZnO在其基态纤锌矿结构仍然是一个挑战。在这里，我们详细介绍了如何$p$型氧化锌可以实现在亚稳态，高压岩盐相（也宽隙）与锂作为外部掺杂剂。利用现代第一性原理缺陷理论，我们预测锂掺杂岩盐相$p$型优先取代锌，并引入浅受主能级。补偿施主如间隙Li和/或氢（普遍存在于纤锌矿相中）的形成受到岩盐结构的紧密堆积性质的抑制，岩盐结构还表现出促进低空穴有效质量和空穴离域的相对高的绝对价带边缘。在富O合成条件下，预测所得的自由空穴浓度超过$\sim10^{19}$ cm $^{-3}$，而在贫O条件下，系统保持$n$型可掺杂。除了揭示令人信服的机会，在实现长期寻求的$p$型ZnO的亚稳态岩盐结构，我们的研究结果提出了多态性作为一个有前途的路线，克服强掺杂不对称的宽带隙氧化物。
英文摘要：
Despite decades of efforts, achieving $p$-type conductivity in the wide band gap ZnO in its ground-state wurtzite structure continues to be a challenge. Here we detail how $p$-type ZnO can be realized in the metastable, high-pressure rocksalt phase (also wide-gap) with Li as an external dopant. Using modern first-principles defect theory, we predict Li to dope the rocksalt phase $p$-type by preferentially substituting for Zn and introducing shallow acceptor levels. Formation of compensating donors like interstitial Li and/or hydrogen, ubiqutous in the wurtzite phase, is inhibited by the close-packed nature of the rocksalt structure, which also exhibits relatively high absolute valence band edge that promotes low hole effective mass and hole delocalization. Resulting concentrations of free holes are predicted to exceed $\sim10^{19}$ cm$^{-3}$ under O-rich synthesis conditions while under O-poor conditions the system remains $n$-type dopable. In addition to revealing compelling opportunities offered by the metastable rocksalt structure in realizing a long-sought $p$-type ZnO our results present polymorphism as a promising route to overcoming strong doping asymmetry of wide-band gap oxides.
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