Design and analysis of electric-field-assisted nonlocal silicon-channel spin devices

Over recent years, spin-MOSFETs (Fig.1) [1] have attracted considerable attention as a key transistor for low-standby-power integrated circuits. To realize spin MOSFETs, understanding and controlling of spin dynamics in the Si channel is indispensable. The Hanle effect of spin-polarized electrons transported in the channel of spin devices is a powerful tool for evaluating spin dynamics. Using the period (B
π
) of Hanle-effect oscillating signals (see Fig. 2), spin lifetime can be calculated accurately [2]. However, there exists a challenge in the generation/measurement of Hanle-effect oscillating signals. The generally used four-terminal nonlocal (4TNL) technique cannot generate sufficient oscillating signals, since this technique employs diffusive spin transport that has a short diffusion length. This technique also causes the widely spread distribution of spin transport time, resulting in the inaccuracy of B
π
[2]. The width of the ferromagnetic contact needs to be carefully designed, since Hanle-effect signals are distorted owing to phase randomizing caused by spin polarized electrons passing through the channel beneath the contact. Inadequate ferromagnetic contact width weakens the satellite peak intensity of Hanle-effect oscillating signals and affects the accuracy of B
π
. Recently, we proposed a new electric-field-assisted (EFA)-4TNL technique based on drift spin transport [2], which makes it possible to measure correct B
π
and evaluate spin lifetime accurately (Fig.3). In the EFA-4TNL technique, the contact width effect can be negligible when an appropriate electric field is applied [2]. In this paper, we computationally analyze Hanle-effect signals of the EFA-4TNL devices and establish an optimization scheme of applied electric field and channel length design of the EFA-4TNL devices. Bulk channel and bottom-gated MOS channel EFA-4TNL devices are investigated (Fig. 3).