Semiconductor Quantum Dot Arrays Research Articles

Electronic state and optical response of a semiconductor quantum dot lattice embedded in an organic host

We investigate a new hybrid exciton state which arises when a regular array of semiconductor quantum dots is placed in a molecular organic medium. The multipolar interaction of excitons in different dots form a type of Wannier–Mott exciton transfering among the dot array. Then a new eigenstate arises owing to strong dipole–dipole coupling of these Wannier excitons of the dots and the Frenkel excitons of the organic molecules. The new state has a large oscillator strength (Frenkel-like) and a large exciton Bohr radius (Wannier-like). Strong enhancement of linear and nonlinear optical responses occurs. Numerical estimates are made for ZnSe dots in a typical organic host.

Spontaneous ordering of nanostructures on crystal surfaces

A review is given of theoretical concepts and experimental results on spontaneous formation of periodically ordered nanometer-scale structures on crystal surfaces. Thermodynamic theory is reviewed for various classes of spontaneously ordered nanostructures, namely, for periodically faceted surfaces, for periodic surface structures of planar domains, and for ordered arrays of three-dimensional coherently strained islands. All these structures are described as equilibrium structures of elastic domains. Despite the fact that driving forces of the instability of a homogeneous phase are different in each case, the common driving force for the long-range ordering of the inhomogeneous phase is the elastic interaction. The theory of the formation of multisheet structures of islands is reviewed, which is governed by both equilibrium ordering and kinetic-controlled ordering. For the islands of the first sheet, an equilibrium structure is formed, and for the next sheets, the structure of the surface islands meets the equilibrium under the constraint of the fixed structures of the buried islands. The experimental situation for the fabrication technology of ordered arrays of semiconductor quantum dots is analyzed, including a discussion of both single-sheet and multiple-sheet ordered arrays.

Strain-driven self-organization of nanostructures on semiconductor surfaces

Theoretical concepts and experimental results on spontaneous formation of periodically ordered nanometer- scale structures on crystal surfaces are reviewed. Thermo- dynamic theory of the formation is considered for various classes of spontaneously ordered nanostructures, namely for periodically faceted surfaces, for periodic surface struc- tures of planar domains, and for ordered arrays of three- dimensional coherently strained islands. All these structures are described as equilibrium structures of elastic domains. Despite the fact that driving forces of the instability of a ho- mogeneous phase are different in each case, the common driving force for the long-range ordering of the inhomo- geneous phase is the elastic interaction. The theory of the formation of multiple-sheet structures of islands is reviewed, which is governed by both equilibrium ordering and kineti- cally controlled ordering. For the islands of the first sheets, an equilibrium structure is formed, and for the next sheets, the structure of the surface islands meets the equilibrium under the constraint of the fixed structures of the buried islands. The experimental situation for the fabrication technology of ordered arrays of semiconductor quantum dots is analyzed where both single-sheet and multiple-sheet ordered arrays are discussed.

Persistent current in an artificial quantum-dot molecule

Using an exact diagonalization technique within a generalized Mott-Hubbard Hamiltonian, we predict the existence of a ground state persistent current in coherent two-dimensional semiconductor quantum dot arrays pierced by an external magnetic flux. The calculated persistent current, which arises from the nontrivial dependence of the ground state energy on the external flux, exists in isolated arrays without any periodic boundary condition. The sensitivity of the calculated persistent current to interaction and disorder is shown to reflect the intricacies of various Anderson-Mott-Hubbard quantum phase transitions in two dimensional systems.

Nonlocal electrodynamics of arrays of quantum dots.

We analyze the linear and nonlinear optical response of an array of quantum dots (QD's). Our model treats the matter-field interaction self-consistently, and includes the nonlocality of the electromagnetic field throughout the system. This procedure allows us to address the dependence of radiative decay rates as well as of the nonlinear response on size, geometry, and the material. Applications are made to a one-dimensional periodic array of semiconductor quantum dots, where the intradot and interdot exciton motion is of Wannier and Frenkel type, respectively. We compare the optical nonlinearity enhancement of the array with that of a single QD.