Al0.6Ga0.4N/GaN/Al0.3Ga0.7N/Al0.6Ga0.4N量子阱中的Rashba自旋劈裂

正如人们所知, 可以通过电场或者设计非对称的半导体异质结构来调控体系的结构反演不对称性(SIA)和Rashba自旋劈裂. 本文研究了Al_0.6Ga_0.4N/GaN/Al_0.3Ga_0.7N/Al_0.6Ga_0.4N量子阱中第一子带的Rashba 系数和Rashba自旋劈裂随Al_0.3Ga_0.7N插入层(右阱)的厚度w_s以及外加电场的变化关系, 其中GaN层(左阱)的厚度为40-w_s Å. 发现随着w_s的增加, 第一子带的Rashba系数和Rashba自旋劈裂首先增加, 然后在w_s>20 Å 时它们迅速减小, 但是w_s>30 Å时Rashba自旋劈裂减小得更快, 因为此时k_f也迅速减小. 阱层对Rashba系数的贡献最大, 界面的贡献次之且随w_s变化不是太明显, 垒层的贡献相对比较小. 然后, 我们假w_s=20 Å, 发现外加电场可以很大程度上调制该体系的Rashba系数和Rashba自旋劈裂, 当外加电场的方向同极化电场方向相同(相反)时, 它们随着外加电场的增加而增加(减小). 当外加电场从-1.5×10⁸ V·m^-1到1.5×10⁸ V· m^-1变化时, Rashba系数随着外加电场的改变而近似线性变化, Rashba自旋劈裂先增加得很快, 然后近似线性增加, 最后缓慢增加. 研究结果表明可以通过改变GaN层和Al_0.3Ga_0.7N层的相对厚度以及外加电场来调节Al_0.6Ga_0.4N/GaN/Al_0.3Ga_0.7N/Al_0.6Ga_0.4N量子阱中的Rashba 系数和Rashba自旋劈裂, 这对于设计自旋电子学器件有些启示.

Rashba spin splitting in the Al0.6Ga0.4N/GaN/Al0.3Ga0.7N/Al0.6Ga0.4N quantum well

As is well known, the structure inversion asymmetry (SIA) and Rashba spin splitting of semiconductor heterostructure can be modulated by either electric field or engineering asymmetric heterostructure. In this paper, we calculate the Rashba coefficient and Rashba spin splitting for the first subband of Al_0.6Ga_0.4N/GaN/Al_0.3Ga_0.7N/Al_0.6Ga_0.4N QW each as a function of thickness (w_s) of the inserted Al_0.3Ga_0.7N layer (right well) and external electric field. The thickness of GaN layer (left well) is 40-w_s Å. With w_s increasing, the Rashba coefficient and Rashba spin splitting for the first subband increase first, because the polarized electric field in the well region increases and the electrons shift towards the left heterointerfaces, and then decrease when w_s>20 Å since the electric field in the well region decreases, and the confined energy increases as effective well thickness decreases. But when w_s>30 Å, the Rashba spin splitting decreases more rapidly, since k_F decreases rapidly. Contributions to the Rashba coefficient from the well is largest, lesser is the contribution from the interface, which varies slowly with w_s, and the contribution from the barrier is relatively small. Then we assume w_s=20 Å, and find that the external electric field can modulate the Rashba coefficient and Rashba spin splitting greatly because the contribution to the Rashba coefficient from the well changes rapidly with the external electric field, and the external electric field brings about additional potential and affects the spatial distribution of electrons, confined energy and Fermi level. When the direction of the external electric field is the same as (contrary to) the polarization electric field, the Rashba coefficient and Rashba spin splitting increase (decrease) with external electric field increasing. With the external electric field changing from -1.5×10⁸ V· m^-1 to 1.5×10⁸ V· m^-1, the Rashba coefficient approximately varies linearly, and the Rashba spin splitting first increases rapidly, then approximately increases linearly, and finally increases slowly. Because the value of k_F increases rapidly first, then increases slowly. Results show that the Rashba coefficient and the Rashba spin splitting in the Al_0.6Ga_0.4N/GaN/Al_0.3Ga_0.7N/Al_0.6Ga_0.4N QW can be modulated by changing the relative thickness of GaN and Al_0.3Ga_0.7N layers and the external electric field, thereby giving guidance for designing the spintronic devices.