$\boldsymbolβ$ -Ga $_2$ O $_3$中Ga空位的劈裂和正电子湮没谱的异常强各向异性
Split Ga vacancies and the unusually strong anisotropy of positron annihilation spectra in $\boldsymbolβ$-Ga$_2$O$_3$
摘要：
本文报道了对$β$ $_2$ O $_3$晶格和Ga单空位缺陷中正电子湮没参数的系统的第一性原理研究，并补充了正电子-电子湮没的多普勒展宽的取向相关实验。我们发现$β$ -Ga $_2$ O $_3$晶格和所考虑的缺陷在它们的多普勒展宽信号中都表现出异常强的各向异性。该各向异性与$β$ $_2$ O $_3$晶体结构的低对称性相关，这导致即使在晶格中的离域状态下也不寻常的正电子一维约束.特别是，最近通过扫描透射电子显微镜观察到的分裂Ga空位产生异常各向异性的正电子湮没信号。我们发现在实验中，$β$ O $_3$样品中的正电子湮没信号似乎常常由分裂的Ga空位支配。
英文摘要：
We report a systematic first principles study on positron annihilation parameters in the $β$-Ga$_2$O$_3$ lattice and Ga mono-vacancy defects complemented with orientation-dependent experiments of the Doppler broadening of the positron-electron annihilation. We find that both the $β$-Ga$_2$O$_3$ lattice and the considered defects exhibit unusually strong anisotropy in their Doppler broadening signals. This anisotropy is associated with low symmetry of the $β$-Ga$_2$O$_3$ crystal structure that leads to unusual kind of one-dimensional confinement of positrons even in the delocalized state in the lattice. In particular, the split Ga vacancies recently observed by scanning transmission electron microscopy produce unusually anisotropic positron annihilation signals. We show that in experiments, the positron annihilation signals in $β$-Ga$_2$O$_3$ samples seem to be often dominated by split Ga vacancies.
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