应变锗的导带结构计算与分析

Calculation and analysis of the conduction band-structure of strained Germanium

应用胡克定律,建立了单、双轴张应力作用下应变锗在任意面内沿<001>、<110>和<111>方向的应变张量模型.根据线性形变势能理论,计算了单轴应力沿<001>、<110>和<111>方向作用下以及双轴应力在不同晶面内的应变锗导带各个能谷的谷底能级的变化情况.计算结果显示,在<001>方向的单轴应力作用下,Δ能谷带边能级分裂,且在压应力为1.8GPa时,Δ能谷的谷底能级变为最低能级.在<110>方向的单轴应力作用下,Δ能谷和L能谷带边能级分裂.在<111>方向的单轴应力作用下,L能谷带边能级分裂.并且随着应力的增加,所有能谷最低能级下降.而在双轴张应力作用下,当面内应变张量达到1.8%时,(001)面应变锗的Γ能谷最低,能级比Δ能谷最低能级还要低.这表明,应变锗由间接带隙半导体变为直接带隙半导体.所得到的结果可为应变锗半导体器件和光电器件的设计提供参考.

This paper estabilishes the strained-tensor model by Hooke＇s law and calculates the energy-level shifts of L, △ and L valleys by the deformation potential theory. By enforcing the uniaxial stress in germanium along （001） direction, the edge band of the △ valley is split with the bottom energy-level being the lowest one among all valleys when the compressive stress is 1.8 GPa. When the strained direction is （110）, the edge bands of L and △ valleys are split. The L valley is split as the strained direction is 〈111〉. When the biaxial tensile-strain is applied, we obtain the conclusion that the strained Ge can become the direct band gap from the indirect band gap as a tensile in-plane strain is 1.8 %.