Ge-Ⅲ亚稳相光学性质的第一性原理研究

First principles study on optical properties of Ge-Ⅲ metastable phase

采用基于密度泛函理论的第一性原理方法研究了Ge-Ⅲ亚稳相的电子结构和光学性质。Ge-Ⅲ相晶体是一种直接带隙半导体（带隙为0.46 eV）。对光学函数的计算表明,Ge-Ⅲ相晶体是一种具有高介电常数和高折射率的晶体。其静介电常数ε1（0）和静态折射率n（0）分别为33.9和5.82,大于相应的Ge-Ⅰ相晶体的值（16和4.0）。光子能量在2.38-14.9 eV（等离子体能量Ep）范围内,ε1（ω）〈0,整个晶体显示金属性;在高频透明区（能量大于Ep）,ε1（ω）〉0,显示介电性。从光吸收谱上看,Ge-Ⅲ相晶体的主要光吸收区位于整个可见光及部分紫外光谱区,在能量为4.51eV处达到最大值2.77×10^5cm^-1。Ge-Ⅲ相晶体的透过率在0-0.46eV范围可达0.5,表明它可作为一种红外光学材料。在高能区（大于14.9 eV）,反射率随能量的增加而骤减,透过率随能量的增加急剧增大,整个晶体表现出紫外透过的特征。能量损失谱上只有一个特征峰位于14.9 eV,对应于Ge-Ⅲ相晶体的等离子体能量。

The electronic structure and optical properties of the Ge-III phase are theoretically studied using first principles calculation based on the density functional theory. The results reveal that the Ge-Ⅲ phase is a direct band gap semiconductor with a small band gap of 0.46 eV. The calculated static dielectric constant ε1（0） and static refractive index n（0） of the Ge-Ⅲ phase are 33.9 and 5.82, respectively, larger than those of the corresponding calculated values of Ge-I phase （16 and 4.0）. In the range of photon energy from 2.38 to 14.9 eV （plasmon energy Ep）, ε1（ω）〈0, the crystal exhibits properties, while if the energy is higher dielectric features are observed. The main absorption region covers the whole visible light and partly the ultraviolet region with a maximum value of 2.77×10^5 cm^-1 at 4.51 eV. The transmittance within the energy range of0-0.46 eV can reach up to 0.5, suggestting that the Ge-Ⅲ phase crystal can be used as an infrared optical material. At high energy region （higher than 14.9 eV）, the reflectivity decreases rapidly as the increase of energy, whereas the transmittance increases sharply as the increases of energy, whereas the transmittance sharply increases. Only one main peak is detected in the energy-loss spectrum has only one main peak appears at 14.9 eV, corre- sponding to the plasmon energy of the Ge-Ⅲ phase.