Ge掺杂SiC电学和光学特性的理论研究

Theoretical Study of Electrical and Optical Properties of Ge-Doped 6H-SiC

基于第一性原理的密度泛函理论(DFT)赝势平面波方法,对Ge掺杂(GexSi1-xC)的6H-Si C电学、光学特性进行了理论计算和分析。杂质形成能的计算结果表明,Ge原子占据Si位后能量更低,更加稳定。通过对电子结构、态密度和光学性质的比较发现,6H-Si C的价带顶主要由C的2 p态占据,而导带底由Si的3 p态占据。随着更多的Ge掺入,导带底位置逐渐由Si的3 p态电子决定转变为Ge的4 p态电子决定,同时导带底向低能方向移动,带隙变窄。比较介电常数发现,对Ge掺入最多的Ge0.333Si0.667C,其电子跃迁机理比6H-Si C简单,吸收边及最大吸收峰分别向低能方向红移了0.9 e V及3.5 e V。

Electronic structure and optical properties of Ge-doped 6H-SiC （GexSi1-xC） are calculated by ultra- soft pseudopotential technology of total energy-plane wave based on the density functional theory. The formation energy of impurities illustrates that Ge dopants prefer to occupy the substitutional Si sites for lower energy and more stable state. Analysis band structures, density of states and optoelectronic characteristics of 6H-SiC shows that the valence band maximum is determined by C-2p states and the conduction band minimum is occupied by the Si-3p orbital. With more Ge content is incorporated within the structure, the conduction band minimum of GexSi1-xC has moved to lower energy and changes to be determined by Ge-4p states. Dielectric function illustrates that the electronic transition in Ge0.333Si0.667C which has a maximum Ge content is more simple than in 6H-SiC, and it＇s absorption edge and peaks are red-shifted to lower energy by 0.9 eV and 3.5 eV, respectively.