Multifield-Manipulated Transport Properties Of Semiconductors

According to the predication of Moore's law,traditional semiconductor electronic devices will soon reach their limits.On the other side,spintronic devices based on electron spin properties also exist the shortcoming of low spin conversion efficiency.The methods that use the coupling of multi-fields,such as electric field,magnetic field,light field and phonon field to control traditional semiconductor devices and spintronic devices will not only provide semiconductors with more functionality and applications to bypass the limits of Moore's law,but also provide more ideas for reducing the critical current density of spintronic devices and generating spin current.In this thesis,we first study the regulation of multi-field coupling on the transport properties of p-n junction,the core component of traditional electronics.Specifically,we study the large magnetoresistance(MR)effect and photo-induced MR effect of p-n junction,as well as the mechanism behind them.Then,the theory of three methods of spin current generated by surface acoustic wave(SAW)based on the acoustic ferromagnetic resonance(acoustic FMR)effect,spin rotation coupling effect and acoustic spin Hall effect is reviewed in detail.Furthermore,the experimental study of SAW in reducing the power consumption in spintronic devices is carried out.The main results are summarized as follows:(1)We present a simple model based on the classic Shockley model to explain the magnetotransport in nonmagnetic p-n junctions.Under a magnetic field,the carriers are deflected by the Lorentz force to redistribute the space charge region(SCR).Owing to the variation of the SCR in the p-n junction,a concentration gradient is formed,which leads to a transverse diffusion process to balance the Lorentz force.The analysis further showed that the SCR has a trapezoidal distribution under a magnetic field,and the slopes of the two sides are related to the product of mobility and magnetic field.The calculated I-V characteristics and MR characteristics of the p-n junction are consistent with the experimental results,proving the accuracy of the model.Moreover,we suggest that the MR of the p-n junction can be enhanced by both enhancing the mobility and modulating the donor concentration to equal the acceptor concentration.Our computer simulation results reveal the origin of MR in the p-n junction and indicate a new avenue for magnetoelectric devices based on semiconductors.(2)By combining magnetoelectric and photovoltaic effects of p-n junctions,we find a novel light-induced MR effect,that the photovoltage in the conventional p-n junction can be significantly tuned by magnetic field.Compared with symmetric MR of p-n junction without illumination,the MR of p-n junction with illumination presents an obvious asymmetry with respect to external magnetic induction(B),namely MR(B)~1MR(-B).Theoretical fits using photovoltaic transport equations further reveal that the asymmetric MR induced by light directly reflects the asymmetric geometric of the SCR in p-n junction under the magnetic induction.The results not only further confirm our MR model of p-n junction,but also indicate that the conventional p-n junction can be used as a multifunctional material based on the interplay between magnetic,optic and electronic response together,which is significant for future semiconductor industry.(3)The SAW is used to reduce the critical current density J_C of the spintronic device Pt/Co/Ta.By the second harmonic Hall measurements,we find that the damping-like spin-orbit torque(SOT)effective field is almost the same with or without SAW,implying that the reduction of₍(8) does not originate from the enhancement of the SOT.However,the current-induced domain wall velocity v under SAW is greatly enhanced.By fitting with the creep law under SAW,we find that ln v is linear with SAW power P,which reveals that the effective pinning barrier is reduced linearly with increasing P.This can be explained by the increase of the average domain nucleation probability caused by the magnetoelastic energy of SAW.The results shed light on the application of SAW-assisted spintronic devices for low consumption storage.