Ge_(64-x)C_(x)合金的能带结构和光学性质的第一性原理计算

First-principles calculation of electronic structures and optical properties of Ge_(64-x)C_(x)alloys

基于第一性原理密度泛函理论(DFT),广义梯度近似下的GGA+U方法,计算了Ge_(64-x)C_(x)(x=0~3)合金体系的能带结构和光学性质.计算结果显示,纯Ge的带隙宽度数值与实验值相符,为0.732 eV.在本文所研究的C浓度范围内Ge_(64-x)C_(x)(x=1~3)均转变成直接带隙,带隙随C原子的增加逐渐减小.光学性质的计算结果表明,C原子引入对所有的光学性质均产生影响,随着C浓度的增加Ge_(64-x)C_(x)合金的静态介电常数增大,在近红外区的吸收系数增大,且吸收光谱红移,对于Ge_(61)C_(3)吸收边延伸至中红外区.C原子掺杂使体系对光的利用率增强,Ge_(64-x)C_(x)合金的载流子寿命和光催化能力也随C浓度的变化而变化.Ge_(64-x)C_(x)合金有希望成为在近红外、中红外区域的光学材料.

The band structures,densities of states and optical properties of Ge_(64-x)C_(x)(x=0~3)alloys are studied from the generalized gradient approximation+U(GGA+U)method based on the first principles density functional theory(DFT).The calculated results show that the band gap width of pure Ge is 0.732 eV,which is in good agreement with the experimental value.In the range of C content studied,Ge_(64-x)C_(x)(x=1~3)transform into the direct band gap.Band gap decreases with the increase of C atom.The calculation results of optical properties show that the introduction of C atom has an effect on the size and position of the imaginary part peak of the dielectric function.With the increasing C content,the static dielectric constant of Ge_(1-x)C_(x) alloys and the absorption coefficient of Ge_(1-x)C_(x) alloys in the near infrared region increase,the absorption spectrum redshifts,the absorption edge of Ge_(61)C_(3) is extended to the mid infrared region.C atom doping enhances the light utilization of the system.The carrier lifetime and photocatalytic activity of Ge_(1-x)C_(x) alloys also change with the change of C concentration.So Ge_(1-x)C_(x) alloys are promising to become an optical material in the near-infrared and mid infrared regions.