We present a theoretical analysis of the electronic properties of type-II $$\hbox {GaAs}_{1-x} \hbox {Sb}_{x}$$ /GaAs quantum rings (QRs), from the perspective of applications in intermediate band solar cells (IBSCs). We outline the analytical solution of Schrodinger’s equation for a cylindrical QR of infinite potential depth, and describe the evolution of the QR ground state with QR morphology. Having used this analytical model to elucidate general aspects of the electronic properties of QRs, we undertake multi-band k·p calculations—including strain and piezoelectric effects—for realistic $$\hbox {GaAs}_{1-x} \hbox {Sb}_{x}$$ /GaAs QRs. Our k·p calculations confirm that the large type-II band offsets in $$\hbox {GaAs}_{1-x} \hbox {Sb}_{x}$$ /GaAs QRs provide strong confinement of holes, and further indicate the presence of resonant (quasi-bound) electron states which localise in the centre of the QR. From the perspective of IBSC design the calculated electronic properties demonstrate several benefits, including (i) large hole ionisation energies, mitigating thermionic emission from the intermediate band, and (ii) electron-hole spatial overlaps exceeding those in conventional $$\hbox {GaAs}_{1-x} \hbox {Sb}_{x}$$ /GaAs QDs, with the potential to engineer these overlaps via the QR morphology so as to manage the trade-off between optical absorption and radiative recombination. Overall, our analysis highlights the flexibility offered by the QR geometry from the perspective of band structure engineering, and identifies specific combinations of QR alloy composition and morphology which offer optimised sub-band gap energies for QR-based IBSCs.

中文翻译：

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II型$$\hbox {GaAs}_{1-x} \hbox {Sb}_{x}$$/GaAs 量子环的电子特性在中带太阳能电池中的应用

我们从应用的角度对 II 型 $$\hbox {GaAs}_{1-x} \hbox {Sb}_{x}$$ /GaAs 量子环 (QRs) 的电子特性进行了理论分析在中带太阳能电池（IBSC）中。我们概述了具有无限潜在深度的圆柱形 QR 的薛定谔方程的解析解，并用 QR 形态描述了 QR 基态的演变。使用这个分析模型来阐明 QR 电子特性的一般方面后，我们进行了多波段 k·p 计算——包括应变和压电效应——用于现实 $$\hbox {GaAs}_{1-x} \hbox { Sb}_{x}$$ /GaAs QR。我们的 k·p 计算证实 $$\hbox {GaAs}_{1-x} \hbox {Sb}_{x}$$ /GaAs QR 中的大 II 型带偏移提供了对空穴的强限制，并进一步表明存在于 QR 中心的共振（准束缚）电子态。从 IBSC 设计的角度来看，计算出的电子特性证明了几个好处，包括 (i) 大空穴电离能，减轻中间带的热电子发射，以及 (ii) 电子 - 空穴空间重叠超过传统 $$\hbox {GaAs }_{1-x} \hbox {Sb}_{x}$$ /GaAs QD，有可能通过 QR 形态设计这些重叠，以管理光吸收和辐射复合之间的权衡。总的来说，我们的分析从能带结构工程的角度突出了 QR 几何提供的灵活性，