第一性原理研究［111］晶向硅纳米线电子结构，光学性质与压阻特性的应变效应

摘要

The influences of strain on the electronic structure , optical properties and piezoresistive properties of [111] silicon nanowires have been investigated by the first -principles method based on the density function the-ory with the generalized gradient approximation .The results of band structure and optical properties indicate that:the band gap of [111] silicon nanowires decreases linearly with the increasing compressive strain , and the band gap becomes indirect under the compressive strain;While under the tensile strain , the band gap is still di-rect, but it decreases slightly , and the upper of the valence band of the silicon nanowires is significantly changed .Based on the strain effect of the band structure , optical properties of the silicon nanowires should be changed greatly:in the case of tensile strain , the dielectric peak of the silicon nanowires appeared wide phenom-enon, the optical absorption enhancement in the low energy region , the static refractive index and the peak value of reflectivity spectrum are increased , however , the compressive strain effect on the optical properties is oppo-site.The results of the piezoresistive properties for the silicon nanowires obtained by combining the band struc -ture and the calculation model of piezoresistive coefficient indicate that: When the [ 111 ] silicon nanowires are compressed , the variation of the piezoresistive coefficient with strain is monotonic , which is mainly attributed to the significant change of the hole concentration;Under tensile strain , the variation of the piezoresistive coefficient is fluctuate, which is mainly due to the competition of the increase of effective transmission mass of the hole and the increase of carrier concentration .In a word, the strain effect should be considered when designing the optoe-lectronic and force devices using the silicon nanowires .%基于密度泛函理论体系下的广义梯度近似（GGA），利用第一性原理方法计算研究了单轴应变对[111]晶向硅纳米线的电子结构、光学性质以及压阻性质的影响。能带结构和光学性质的结果表明：压应变导致硅纳米线的带隙明显线性减小，且使其由直隙半导体转变为间隙半导体，而施加拉应变后硅纳米线仍为直隙半导体材料，但是带隙略有减小，且价带顶附近的能带线产生了较为复杂的变化。由于能带的应变效应导致其光学性质也相应发生了较大改变：拉应变使硅纳米线的介电峰出现宽化现象，低能区内的光吸收增强，静态折射率和反射率峰值增大，而压应变的效果则相反。结合能带结构与压阻系数计算模型得到的压阻特性结果表明：随着压应变的增加压阻系数单调减小，这主要归因于空穴浓度随压应变显著变化引起的；而拉应变作用时，压阻系数呈现波动趋势，这主要是由于空穴有效传输质量的增加程度和载流子浓度的增加程度不同而相互竞争导致的。上述计算结果表明，设计基于硅纳米线的光电和力电器件时，需考虑其应变效应。