采用基于密度泛函理论的第一性原理方法计算了钛(Ti)掺杂纳米Si晶的形成能、电子结构和光学性质,考虑了Ti占据替代和间隙不同位置的构型特点.结果表明:所有的掺杂结构都是不稳定的,中心四面体间隙Ti掺杂纳米硅晶最接近稳定结构.Ti 3d态分裂为t2g和eg态.对于Ti替代掺杂,eg在带隙中提供一个空带,不能产生受体态;对于四面体间隙Ti掺杂,部分填充的t2g态出现在带隙中,其形成的杂质能级可满足杂质带材料的要求.由间隙Ti掺杂Si纳米晶的介电函数虚部和光吸收系数可知,Ti的掺入可增强对太阳光谱的吸收强度.
The formation energies,electronic structures and optical properties of Ti-doped silicon nanocrystals were calculated by first-principles based on density functional theory.We considered configurational characteristics of the substitutional sites and the interstitial sites.The results show all of the sites are energetically unfavorable,and Ti atoms setting in the center tetrahedron interstitial position of Si nanocrystals implies the energetic balance closest to the eguilibrium.The 3d orbits of Ti split into t2g triplet and eg doublet.It is observed that substitutional Ti causes eg manifolds to appear inside the band gap.However,they cannot produce by themselves any donor level because they are empty.Interstitial Ti causes the partially filled t2g manifolds to appear inside the band gap.An impurity band fulfilling all the requirements of an intermediate-band material is formed in the silicon nanocrystals.The imaginary parts of dielectric function and optical absorption on interstitially Ti show that the doping can strengthen the absorbing intensity of solar spectrum lower than 3 eV.
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