论文标题
从头算的合奏平均值光学，运输和热电特性的六角形Si $ _x $ ge $ _ {1-x} $合金
Ensemble averages of ab initio optical, transport, and thermoelectric properties of hexagonal Si$_x$Ge$_{1-x}$ alloys
论文作者
论文摘要
我们提出了对基于密度功能的理论计算，Boltzmann运输方程的纯和掺杂的六角形Si $ _x $ ge $ _ {1-x} $合金的纯和掺杂的六角形Si $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x $ _x的全面研究，并提出了全面的第一原告研究。在低温下，对六角基晶体的相位分解在热力学上受到青睐，但预计室温随机合金周围及以上是稳定的。尽管六角形Si具有间接的带隙，但六角形GE的间隙是直接的，在吸收边缘的光学转变非常弱。对于低于45 \，\％的Si含量的合金带隙仍然保持直接，并且最低光学转变的振荡器强度通过合金有效增强。光谱显示清晰的趋势，并且可以用组成调节吸收边缘和突出峰。在立方和六角合金中，转运系数对载体浓度和温度的依赖性相似。但是，由于六角形对称性减少，后者显示出各向异性反应。特别是，转运质量表现出显着的方向依赖性。 $ N $掺杂的合金的Seebeck系数和热电功率因子与SI含量无独立于温度显示出非单调的变化。
We present a comprehensive first-principles investigation of optical, transport, and thermoelectric properties of pure and doped hexagonal Si$_x$Ge$_{1-x}$ alloys based on density-functional theory calculations, the Boltzmann transport equation, and the generalized quasi-chemical approximation to obtain alloy averages of electronic properties. At low temperature, phase decomposition into the hexagonal elementary crystals is thermodynamically favored, but around and above room temperature random alloys are predicted to be stable. While hexagonal Si has an indirect band gap, the gap of hexagonal Ge is direct with very weak optical transitions at the absorption edge. The alloy band gap remains direct for a Si content below 45\,\% and the oscillator strength of the lowest optical transitions is efficiently enhanced by alloying. The optical spectra show clear trends and both absorption edges and prominent peaks can be tuned with composition. The dependence of transport coefficients on carrier concentration and temperature is similar in cubic and hexagonal alloys. However, the latter display anisotropic response due to the reduced hexagonal symmetry. In particular, the transport mass exhibits a significant directional dependence. Seebeck coefficients and thermoelectric power factors of $n$-doped alloys show non-monotonous variations with the Si content independently of temperature.
