School of Electrical and Computer Engineering and Network for Computational Nanotechnology, Purdue University, West Lafayette, IN 47906, USA.
Nanotechnology. 2011 Aug 5;22(31):315709. doi: 10.1088/0957-4484/22/31/315709. Epub 2011 Jul 8.
Atomistic electronic structure calculations are performed to study the coherent inter-dot couplings of the electronic states in a single InGaAs quantum dot molecule. The experimentally observed excitonic spectrum by Krenner et al (2005) Phys. Rev. Lett. 94 057402 is quantitatively reproduced, and the correct energy states are identified based on a previously validated atomistic tight binding model. The extended devices are represented explicitly in space with 15-million-atom structures. An excited state spectroscopy technique is applied where the externally applied electric field is swept to probe the ladder of the electronic energy levels (electron or hole) of one quantum dot through anti-crossings with the energy levels of the other quantum dot in a two-quantum-dot molecule. This technique can be used to estimate the spatial electron-hole spacing inside the quantum dot molecule as well as to reverse engineer quantum dot geometry parameters such as the quantum dot separation. Crystal-deformation-induced piezoelectric effects have been discussed in the literature as minor perturbations lifting degeneracies of the electron excited (P and D) states, thus affecting polarization alignment of wavefunction lobes for III-V heterostructures such as single InAs/GaAs quantum dots. In contrast, this work demonstrates the crucial importance of piezoelectricity to resolve the symmetries and energies of the excited states through matching the experimentally measured spectrum in an InGaAs quantum dot molecule under the influence of an electric field. Both linear and quadratic piezoelectric effects are studied for the first time for a quantum dot molecule and demonstrated to be indeed important. The net piezoelectric contribution is found to be critical in determining the correct energy spectrum, which is in contrast to recent studies reporting vanishing net piezoelectric contributions.
采用原子电子结构计算方法研究了单个 InGaAs 量子点分子中电子态的相干点间耦合。Krenner 等人（2005 年）实验观察到的激子能谱Phys. Rev. Lett. 94 057402 被定量重现，并且基于先前验证的原子紧束缚模型识别了正确的能级。扩展器件在空间中用 1500 万个原子结构明确表示。应用激发态光谱技术，外部施加的电场被扫过，通过与双量子点分子中另一个量子点的能级交叉，探测一个量子点的电子能级（电子或空穴）的能级梯。该技术可用于估计量子点分子内部的电子空穴间距，以及反向工程量子点几何参数，例如量子点分离。晶体变形诱导的压电效应已在文献中被讨论为轻微扰动消除电子激发（P 和 D）态的简并，从而影响 III-V 异质结构（如单个 InAs/GaAs 量子点）的波函数瓣的极化排列。相比之下，这项工作证明了压电性的重要性，通过在电场影响下匹配实验测量的 InGaAs 量子点分子中的光谱，解决了激发态的对称性和能量问题。首次研究了量子点分子中的线性和二次压电效应，并证明它们确实很重要。发现净压电贡献对于确定正确的能谱至关重要，这与最近报道的净压电贡献为零的研究结果形成对比。
