外加电场和Al组分对纤锌矿AlGaN/GaN量子阱中的电子g因子的影响

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(S_//~(bulk)和g⊥)是构成g⊥=(g//-g_0)=g_//~(bulk)的主要部分,但g_//~(bulk)和g⊥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,g_//~(bulk)和g_⊥~(bulk)的强度同时增加(减小).当外加电场从-1.5×10~8 V·m~(-1)到1.5×10~8 V·m~(-1)变化时,异质结界面对g⊥的贡献(Γ_(Inter))大于0且强度缓慢增加,阱层对g⊥的贡献(Γ_W)小于0且强度也缓慢增加.然而Γ_(Inter)的强度比Γ_w大,且后者的强度随着外加电场的改变增加较快,所以δg0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(S_(1,2)=0),g_//~(bulk)和g⊥的强度同时减小,然而考虑应变效应后(S_(1,2)≠0),β_1g⊥和γ1(g_//~(bulk))的强度随着Al组分的增加而增加.随着垒层Al组分的增加,Γ_(Inter)和Γ_w的强度都增加,但Γ_(Inter)的强度较大且增加得较快,所以的的强度缓慢增加.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g⊥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.

Effects of external electric field and Al content on g factor of wurtzite AlGaN/GaN quantum wells

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 Δg_┴=(g_┴-g₀)=g_┴^bulk + g^w and Δg_//=(g_//-g₀)=g_//^bulk are mainly contributed by the bulk structure (g_//^bulk and g_┴^bulk) respectively, but the difference between g_//^bulk and g_┴^bulk 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 (g^w) is considerable. When the direction of the external electric field is the same as (opposite to) the polarization electric field, the magnitudes of g_//^bulk and g_┴^bulk 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 energy ε₁ increases slowly, and the magnitude of the envelope function at the left heterointerface increases. So the contribution to Δg_┴ from the heterointerface Γ_Inter is positive and increases slowly, and that from the well Γ_W is negative and increases slowly in magnitude. The magnitude of Γ_Inter is larger than that of Γ_W, 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 (g_┴^bulk) and <γ>₁ (g_//^bulk) decrease if the strain effects are ignored (S_{1, 2}=0), because the confined energy decreases and the peak of the envelope function shifts towards the left heterointerface. By considering the strain effects (S_{1, 2} ≠ 0), the magnitude of <β>₁ (g_┴^bulk) and <γ>₁ (g_//^bulk) 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 > z_p, which the situation for γ (z) is similar to. With increasing Al content, the magnitudes of Γ_Inter and Γ_W both increase, but the magnitude of Γ_Inter is larger and increases more rapidly. Therefore δg increases slowly. The magnitude of Δ g_┴ first decreases with increasing Al content, then it increases with Al content increasing, and since g_┴^bulk <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.