单斜(Al$_x$Ga$_{1{\rm -}x})_2$O$_3$合金中供体补偿的起源
Origin of donor compensation in monoclinic (Al$_x$Ga$_{1{\rm -}x})_2$O$_3$ alloys
AI总结：
研究揭示单斜(Al$_x$Ga$_{1{\rm -}x})_2$O$_3$合金中供体补偿的机制，通过密度泛函理论分析发现空位能量低于Si供体，导致补偿效应。
摘要：
(Al$_x$Ga$_{1{\rm -}x})_2$O$_3$合金常用于与单斜Ga$_2$O$_3$异质结中，导致较大的导带偏移，从而产生电荷载流子限制，这一性质对器件应用具有吸引力。然而，当(Al$_x$Ga$_{1{\rm -}x})_2$O$_3$合金用Si进行n型掺杂时，最有效的浅层受体，当合金中Al含量超过26%时，电荷载流子数量显著减少，使有意掺杂失效。本文表明，这种补偿是由于阳离子空位在受体掺杂下形成。我们使用HSE06混合泛函的密度泛函理论研究单斜AlGaO$_3$和单斜Al$_2$O$_3$中的阳离子空位。我们发现空位倾向于占据分裂空位配置，类似于Ga$_2$O$_3$中的空位。此外，通过比较空位的形成能与Si受体的形成能，我们证明空位的能量低于Si受体，无论费米能级如何，只要合金中Al含量超过16%，因此阳离子空位将补偿受体掺杂，解释了实验观测。
英文摘要：
(Al$_x$Ga$_{1{\rm -}x})_2$O$_3$ alloys are frequently used in heterostructures with monoclinic Ga$_2$O$_3$, resulting in a large conduction-band offset, which leads to charge carrier confinement, a property that is desirable for device applications. However, when (Al$_x$Ga$_{1{\rm -}x})_2$O$_3$ alloys are $n$-type doped with Si, the most efficient shallow donor, there is a significant reduction in the number of charge carriers when the Al content of the alloys is greater than 26%, rendering intentional doping ineffective. Here we show that this compensation is due to cation vacancies forming in response to donor doping. We use density functional theory with the HSE06 hybrid functional to study cation vacancies in monoclinic AlGaO$_3$ and monoclinic Al$_2$O$_3$. We find that vacancies prefer to occupy split-vacancy configurations, similar to vacancies in Ga$_2$O$_3$. Furthermore, by comparing the formation energy of the vacancy with the formation energy of Si donors, we show that vacancies are lower in energy than Si donors, independent of the Fermi level, as soon as the alloys contain more than 16% Al. Therefore, cation vacancies will compensate the donor doping, explaining experimental observations.
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