Structural characterization of (In,Ga)As quantum dots in a GaAs matrix.

Morphology evolution of molecular-beam-epitaxy-grown InAs and ${\mathrm{In}}_{0.5}$${\mathrm{Ga}}_{0.5}$As layers as a function of deposition thickness, range from 1 to 10 ML, is studied by transmission-electron microscopy to characterize the formation and the self-organization of pseudomorphic quantum dots. For deposition (at 450--480 \ifmmode^\circ\else\textdegree\fi{}C) of 3--7 ML of InAs and 5--10 ML of ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As, respectively, well-developed and crystallographically perfect dots with typical base length of 12 nm and small size dispersion form, which exhibit short-range ordering on a primitive two-dimensional square lattice along 〈100〉. The luminescence from all samples with coherent dots exhibits high quantum efficiency. For 4-ML InAs dots, coincidence of luminescence and absorption is demonstrated. Arrangement of ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As dots in chains along [110] is the result of ordering during deposition at even lower temperatures (\ensuremath{\sim}320 \ifmmode^\circ\else\textdegree\fi{}C).