摘要:
研究了外加电场和垒层的Al组分对AlGaN/GaN量子阱中的横向和纵向g因子(g⊥和g//)及其各向异性(δg)的影响.纤锌矿体结构的贡献(gbulk//和gbulk⊥)是构成?g⊥=(g⊥?g0)=gbulk⊥+gw和?g//=(g//?g0)=gbulk//的主要部分,但gbulk//和gbulk⊥ 的差值很小且几乎不随外加电场和Al组分改变.当外加电场的方向同极化电场的方向相同(相反)且增加时,gbulk//和gbulk⊥ 的强度同时增加(减小).当外加电场从?1.5×108 V·m?1到1.5×108 V·m?1变化时,异质结界面对?g⊥的贡献(ΓInter)大于0且强度缓慢增加,阱层对?g⊥ 的贡献(ΓW)小于0且强度也缓慢增加.然而ΓInter的强度比ΓW大,且后者的强度随着外加电场的改变增加较快,所以δg>0且强度随着外加电场的变化而减小.当垒层的Al组分增加时,如果不考虑应变效应(S1,2=0),gbulk//和gbulk⊥ 的强度同时减小,然而考虑应变效应后(S1,2?=0),?β?1(gbulk⊥)和?γ?1(gbulk//)的强度随着Al组分的增加而增加.随着垒层Al组分的增加,ΓInter和ΓW的强度都增加,但ΓInter的强度较大且增加得较快,所以δg的强度缓慢增加.?g⊥的强度先随着Al组分的增加而减小,然后又随着Al组分的增加而增加,因为gbulk⊥ 小于0且强度随着Al组分增加得很快.结果表明,AlGaN/GaN量子阱结构中的电子g因子及其各向异性可以被外加电场、垒层的Al组分、应变效应和量子限制效应共同调制.
Abstract:
In this paper, we study the effects of external electric field and Al content on the transverse and longitudinal g-factor (g⊥ and g//) and its anisotropy (δg) of wurtzite AlGaN/GaN quantum wells (QWs). The?g⊥=(g⊥?g0)=gbulk⊥ +gw and ?g// = (g// ?g0) = gbulk// are mainly contributed by the bulk structure (gbulk// and gbulk⊥ ) respectively, but the difference between gbulk// and gbulk⊥ is small and almost remains unchanged when the external electric field and Al content are varied. So the anisotropy of the g factor in AlGaN/GaN QWs induced by the bulk wurtzite structure is small, while the anisotropy induced by the quantum confined effect (gw) is considerable. When the direction of the external electric field is the same as (opposite to) the polarization electric field, the magnitudes of gbulk// and gbulk⊥ both increase (decrease) with increasing external electric field. This is induced mainly by the variations of envelope function and confined energy with the electric field. With the external electric field changing from ?1.5 × 108 V·m?1 to 1.5 × 108 V·m?1, the confined energyε1 increases slowly, and the magnitude of the envelope function at the left heterointerface increases. So the contribution to ?g⊥ from the heterointerface ΓInter is positive and increases slowly, and that from the well ΓW is negative and increases slowly in magnitude. The magnitude of ΓInter is larger than that of ΓW , but the magnitude of the latter increases more rapidly. All the above factors make the g-factor anisotropy δg>0 and decrease in magnitude with electric field increasing. With increasing Al content of the barrier, both 〈β〉1 (gbulk⊥ ) and 〈γ〉1 (gbulk// ) decrease if the strain effects are ignored (S1,2 = 0), because the confined energy decreases and the peak of the envelope function shifts towards the left heterointerface. By considering the strain effects (S1,2?=0), the magnitude of〈β〉1 (gbulk⊥ ) and〈γ〉1 (gbulk// ) increase with Al content increasing. The strain effect has a great influence on the confined potential V (z), leading to the rapid increase of β(z) when z > zp, which the situation for γ(z) is similar to. With increasing Al content, the magnitudes of ΓInter and ΓW both increase, but the magnitude of ΓInter is larger and increases more rapidly. Thereforeδg increases slowly. The magnitude of ?g⊥ first decreases with increasing Al content, then it increases with Al content increasing, and since gbulk⊥ <0 it increases more rapidly in magnitude. Results show that the g-factor and its anisotropy in AlGaN/GaN QWs can be greatly modulated by the external electric field, the Al content in the barrier, the strain effects and the quantum confined effect. Results obtained here are of great importance for designing the spintronic devices.
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