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Optical properties of an nanostructure spontaneously formed on GaAs (311)A-oriented substrates

was deposited by molecular beam epitaxy on GaAs (311)A-oriented substrates. This highly strained epilayer forms a three-dimensional surface below the critical thickness for strain relaxation. The surface observed by atomic force microscopy shows a corrugated nanostructure with a period of 35 nm along the (233) direction. The photoluminescence spectrum of a sample where the nanostructure was covered with a GaAs cap layer shows a strong peak at 1.28 eV up to room temperature. The dependence on temperature of the radiative recombination time constant indicates that excitons are confined in a zero-dimensional potential up to 100 K. The presence of the nanostructure under the GaAs cap layer was confirmed by cross sectional TEM.