Ordered arrays of quantum dots: Formation, electronic spectra, relaxation phenomena, lasing

Elastic relaxation on facet edges, renormalization of the surface energy of the facets, and interaction between islands via the strained substrate are the driving forces for self-organization of ordered arrays of uniform coherent three-dimensional islands on crystal surfaces. For a (100) surface of a cubic crystal, two-dimensional square lattice of pyramid-like islands (quantum dots) with the periodicity along the directions of the lowest stiffness [010] and [001] has the minimum energy among different one-dimensional and two-dimensional arrays. For the InAs/GaAs(100) system, an equilibrium array of dots of the lateral size similar to 120-140 Angstrom exists in a fixed range of growth parameters. The main luminescence peak at 1.1 eV, as well as peaks of excited states coincide bl energy with the peaks revealed in the calorimetric absorption spectra regardless of the amount of InAs deposited (2-5 ML). Raman spectra indicate significant strain in InAs dots. The ''phonon bottleneck'' effect is bypassed via multi-phonon exciton and carrier relaxation. Ultranarrow lines(< 0.15 meV) are observed in cathodoluminescence spectra up to high temperatures. Low threshold current density operation via zero-dimensional states and ultrahigh temperature stability of the threshold current (T-0 = 450 K) are realized for a quantum dot injection laser. Increase in the gain and significant reduction in the radiative lifetime are possible via the self-organization of vertically-coupled quantum dots (VECODs) arranged in a well ordered artificial three-dimensional tetragonal lattice.