Quantum Monte Carlo Study on Excitonic Complexes in Quantum Structures

在本研究项目中，我们使用扩散蒙特卡罗方法成功地研究了各种量子结构中的激子复合物或激子、激子分子和带电激子的性质。该方法在有效质量近似下，在很小的统计误差范围内给出了精确的结合能，适用于任何复杂的约束势。我们得到了以下结果：1。GaAs/AlGaAs i型量子阱我们发现双激子结合能几乎是变分方法的两倍。正电荷激子的结合能小于双激子，负电荷激子的结合能小于负电荷激子。对于小于100 A的量子阱，异质界面的粗糙度导致激子复合物的侧向约束，从而导致结合能的强烈增强。在最近的实验中观察到这种增强，并且我们的理论结果很好地再现了实验结果。量子点已经被发现，对于相对较小的点，结合能可以是负的，或者可以强烈地增加。这是由于量子点中的电子和激子空穴之间的约束差而产生的静电势。GaAs/AlAs ii型超晶格由于电子和空穴之间的空间分离，ii型超晶格中的激子具有偶极矩。由于这些激子之间的偶极-偶极相互作用，它们可以沿着生长方向连续结合，形成激子聚合物。预计每个激子的结合能为3mev。量子线中激子复合物的性质介于量子阱和量子点之间。就像在量子点中一样，结合能可以被大大增强，但它们不能是负的。这是因为具有排斥性库仑相互作用的粒子之间的距离可以是无穷大。这意味着我们可以通过控制约束势来阻止某种激子复合物的形成。少

In this research project, we have successfully investigated properties of excitonic complexes or excitons, excitonic molecules, and charged excitons in various quantum structures, using the diffusion Monte Carlo method. This method gives us exact binding energies within a small statistical error under the effective mass approximation and is applicable to any complicated confinement potentials. We have obtained the following results :1. GaAs/AlGaAs type-I quantum wellsWe have found that the biexcitonic binding energies are almost twice of those by variational method. The binding energies for positively charged excitons are smaller than those of biexcitons, and those of negatively charged excitons are smaller than negatively charged ones. For quantum wells narrower than 100 A, the roughness of the heterointerfaces causes lateral confinement of excitonic complexes and resulting strong enhancement of binding energies. This enhancement is observed in recent experiments, and our theoretical … More results reproduce the experimental ones quite well.2. Quantum dotsIt has been found that the binding energies can be negative or can increase strongly for relatively small dots. This comes from the electrostatic potential in a quantum dot resulting from the difference of confinement between an electron and a hole of an exciton in the dot.3. GaAs/AlAs type-II superlatticesBecause of the spatial separation between electron and holes, an exciton in type-II superlattices has dipole moment. Because of the dipole-dipole interaction between these excitons they can bind successively along the growth direction and form an excitonic polymer. The binding energy per excitons of 3 meV is expected.4. Quantum wiresThe properties of excitonie complexes in quantum wires are between those in quantum wells and quantum dots. As in quantum dots, the binding energies can be strongly enhanced, but they cannot be negative. This is because the distance between particles with a repulsive Coulomb interaction between them can be infinity. This means that we can prevent a formation of some kind of excitonic complexes by controlling confinement potentials. Less