Grant-in-Aid for Scientific Research (C).
|Research Institution||Japan Advanced Institute of Science and Technology|
TSUCHIYA Takuma School of Materials Science, Japan Advanced Institute of Science Research Associate, 材料科学研究科, 助手 (40262597)
|Project Fiscal Year
1998 – 2000
Completed(Fiscal Year 2000)
|Budget Amount *help
¥3,400,000 (Direct Cost : ¥3,400,000)
Fiscal Year 2000 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1999 : ¥1,100,000 (Direct Cost : ¥1,100,000)
Fiscal Year 1998 : ¥1,800,000 (Direct Cost : ¥1,800,000)
|Keywords||excitonic molecules / charged excitons / binding energy / quantum structure / diffusion Monte Carlo / GaAs / CdTe / excitons / 励起子分子 / 荷電励起子 / 束縛エネルギー / 量子構造 / 拡散モンテカルロ法 / 励起子 / 量子細線 / タイプII超格子 / 励起子高分子 / 量子モンテカルロ法 / 量子ドット / 荷量励起子 / CuCl / 量子井戸 / 半導体超格子|
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 wells
We 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
results reproduce the experimental ones quite well.
2. Quantum dots
It 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 superlattices
Because 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 wires
The 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