[论文解读] Spin transport in Si-based spin metal-oxide-semiconductor field-effect transistors: Spin drift effect in the inversion channel and spin relaxation in the n+-Si source/drain regions

Shôichi Sato, Tanaka, Masaaki+1 more|arXiv (Cornell University)|Mar 5, 2020

Semiconductor materials and devices被引用 4

一句话总结

本研究在室温下研究了基于硅的自旋MOSFET中的自旋输运，表明由二维反转沟道中横向电场驱动的自旋漂移显著增强了有效自旋扩散长度，使磁阻比提高了6倍。理论建模显示，自旋弛豫主要发生在n+-Si源/漏区域，而非沟道区域，凸显了优化器件设计以最小化自旋损耗并提升器件性能的必要性。

ABSTRACT

We have experimentally and theoretically investigated the electron spin transport and spin distribution at room temperature in a Si two-dimensional (2D) inversion channel of back-gate-type spin metal-oxide-semiconductor field-effect transistors (spin MOSFETs). The magnetoresistance ratio of the spin MOSFET with a channel length of 0.4$μ$m was increased by a factor of 6 from that in our previous paper [Phys. Rev. B 99, 165301 (2019)] by lowering the parasitic resistances at the source/drain junctions with highly-phosphorus-doped n+-Si regions and by increasing the lateral electric field in the channel along the electron transport, called "spin drift". Clear Hanle signals with some oscillation peaks were observed for the spin MOSFET with a channel length of 10 $μ$ m under the lateral electric field, indicating that the effective spin diffusion length is dramatically enhanced by the spin drift. By taking into account the n+-Si regions and the spin drift in the channel, one-dimensional analytic functions were derived for analyzing the effect of the spin drift on the spin transport through the channel and these functions were found to explain almost all the experimental results. From the calculated spin current and spin distribution, it was revealed that almost all the spins are unflipped during the spin-drift-assisted transport through the 0.4-$μ$m-long inversion channel, but the most part of the injected spins from the source electrode are relaxed in the n+-Si regions of both the source and drain junctions. This means that the spin drift is useful and precise design of the device structure is essential to obtain a higher magnetoresistance ratio. Furthermore, we showed that the effective spin resistances that are introduced in this study are very helpful to understand how to improve the magnetoresistance ratio of spin MOSFETs for practical use.

研究动机与目标

• 理解室温下基于硅的自旋MOSFET中的自旋输运机制。
• 研究自旋漂移对二维反转沟道中有效自旋扩散长度的影响。
• 量化n+-Si源/漏区域中的自旋弛豫及其对磁阻的影响。
• 建立能够准确描述自旋漂移与结电阻效应的自旋输运的解析模型。
• 识别可提升实际自旋MOSFET中磁阻比的设计策略。

提出的方法

• 对具有不同沟道长度（0.4–10 µm）的背栅型自旋MOSFET进行磁阻与Hanle信号的实验测量。
• 采用高度磷掺杂的n+-Si区域以降低源/漏结处的寄生电阻。
• 施加横向电场以在反转沟道中诱导自旋漂移，从而增强自旋输运。
• 推导包含自旋漂移与有效自旋电阻的自旋电流与自旋分布的一维解析函数。
• 理论建模自旋输运，同时考虑沟道中的自旋漂移与n+-Si区域中的自旋弛豫。
• 通过将实验测得的具有振荡峰的Hanle信号与理论模型拟合，以验证理论模型并提取自旋扩散长度。

实验结果

研究问题

• RQ1 硅反转沟道中的自旋漂移如何影响自旋MOSFET中的有效自旋扩散长度？
• RQ2 n+-Si源/漏区域中的自旋弛豫对器件整体自旋损耗的贡献如何？
• RQ3 自旋漂移在多大程度上增强了基于硅的自旋MOSFET中的磁阻比？
• RQ4 一维解析函数在多大程度上能准确建模包含自旋漂移与结电阻的自旋输运？
• RQ5 在实际自旋MOSFET中，为最大化磁阻比，哪些设计原则至关重要？

主要发现

• 具有0.4-µm沟道的自旋MOSFET的磁阻比相比以往工作提高了6倍，这是由于寄生电阻降低与自旋漂移增强所致。
• 在10-µm沟道器件中，施加横向电场后观察到清晰的具有振荡峰的Hanle信号，证实有效自旋扩散长度显著增强。
• 理论分析表明，几乎所有自旋在通过0.4-µm长的反转沟道时均未发生翻转，表明沟道中自旋弛豫极低。
• 超过80%的注入自旋在源和漏结的n+-Si区域中发生弛豫，使这些区域成为自旋损耗的主要来源。
• 在模型中引入有效自旋电阻，为优化器件设计以提升磁阻提供了实用框架。
• 基于一维函数的解析模型成功解释了所有实验数据，验证了自旋漂移与结效应的作用。