Simulated self-assembly and optoelectronic properties of InAs/GaAs quantum dot arrays

Numerical simulations are used to compute the quantum confinement and optical absorption spectra of a quantum dot array that is fabricated by the spontaneous formation of islands during deposition of a strained epitaxial film. The epitaxial growth process is first modeled using a continuum finite element method, so the quantum dot array under consideration is itself the result of a computational model. Quantum confinement properties of the resulting island array are then computed by approximating the band structure of the solid using the Luttinger-Kohn k.p Hamiltonian, suitably extended to account for the effects of strain in the islands. The calculations predict the evolution of the spectrum of electron and hole states during self-assembly and coarsening of the island array including a two-dimensional to zero-dimensional electron gas transition at the onset of island self-assembly. For a fully formed array of quantum dots the spectral properties are dominated by inhomogeneous broadening, or the effects of a distribution in size and shape of dots in the array. In particular, there is found to be energy degeneracy between s-type states in smaller quantum dots and p-type or d-type states in larger quantum dots. Also, among the states in the computed electron and hole spectra are some states with strong wave function coupling between pairs of adjacent dots and other states that are delocalized throughout the entire wetting layer. The optical absorption spectrum for the quantum dot array, computed from the electron and hole spectra, compares well with experimental photoemission and absorption data. (C) 2002 American Institute of Physics.