Strained Axial Si/Ge Heteronanowire Devices: From Tunneling Transistors to Optical Sources

我们提议与洛斯阿拉莫斯的T. Picraux外延小组合作，研究由直径小于50 nm的纳米线制成的具有轴向Si/Ge异质结的器件。先前的研究表明，侧壁应变松弛极大地扩展了可用的带隙和应变工程，允许基本上任意SiGe成分的片段被纳入轴向纳米线。我们计划研究以下类型的器件：i)轴向Si/Ge异质线隧道晶体管，由于沿纳米线的带隙和应变工程与栅极全方位器件几何结构相结合，它承诺更锐利的开关和更高的隧道电流的组合；ii)窄异质纳米线临界厚度极限的松弛使得具有高导电性和价带势垒的Si/Ge双势垒隧道结构成为可能；iii)具有横向尺寸限制的Si/Ge/Si pn异质结，由于Ge区更窄和伪直接的带隙，有望实现更强的光学跃迁。实验结果将与连续介质弹性和分子动力学的能带结构数值模拟进行比较（再次与Picraux小组合作）。更广泛的影响具有栅极全方位几何结构的铁纳米线隧道晶体管是与硅技术兼容的低压开关的更现实的候选器件之一。为非均匀应变在~ 10nm尺度上的原子模拟提供实验数据。洛斯阿拉莫斯合作研究将增加研究生教育的影响，因为延长学生访问洛斯阿拉莫斯。本科生将在子部门工作，包括来自少数民族机构的REU学生（通过布朗MRSEC确定）。

INTELLECTUAL MERITWe propose to study devices fabricated from sub-50 nm diameter nanowires with axial Si/Ge heterojunctions grown by the vapor-liquid-solid technique in collaboration with T. Picraux's epitaxy group at Los Alamos. Previous work has shown that sidewall strain relaxation greatly expands the available bandgap and strain engineering, allowing segments of essentially arbitrary SiGe composition to be incorporated into the axial nanowire. We plan to study the following classes of devices:i) axial Si/Ge heteronanowire tunneling transistors, which promise a combination of sharper switching together with higher tunneling currents due to bandgap and strain engineering along the nanowire combined with the gate-all-around device geometry; ii) Si/Ge double-barrier tunneling structures with high conduction and valence band barriers made possible by the relaxation of critical thickness limits in narrow heteronanowires;iii) Si/Ge/Si pn heterojunctions with lateral size confinement that promise stronger optical transitions due to narrower and pseudo-direct bandgap in the Ge region.Experimental results will be compared to numerical band structure simulations from both continuum elasticity and molecular dynamics (again, in collaboration with the Picraux group).BROADER IMPACTHeteronanowire tunneling transistors with gate-all-around geometry comprise one of the more realistic candidates for low-voltage switching compatible with silicon technology. Also, our work will provide experimental data for atomistic simulations of inhomogeneous strain at ~10 nm length scale. The Los Alamos collaboration research will have added graduate education impact due to extended student visits to Los Alamos. Undergraduates will work on sub-sections, including REU students from minority institutions (identified through the Brown MRSEC).