Microscopic excitation spectroscopy for zero-dimensional quantized states of individual ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/${\mathrm{Al}}_{\mathit{y}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{y}}$As quantum dots

We investigate the optical transition of a small number of ${\mathrm{In}}_{0.4}$ ${\mathrm{Ga}}_{0.6}$As quantum dots fabricated by self-organized growth on a (311)B GaAs substrate by microscopic photoluminescence and excitation spectroscopy. The luminescence shows very sharp peaks. By tuning the detection at these peaks, discrete and narrow absorption lines are observed in the excitation spectrum, which are assigned to zero-dimensional (0D) quantized levels. Resonant excitation experiments clarify their discrete nature, which is a manifestation of zero dimensionality. This discreteness allows us to detect a single dot selectively, even when a number of dots are illuminated. Analysis of the homogeneous broadening of these 0D quantized levels indicates that there is no threshold behavior at LO-phonon energy. © 1996 The American Physical Society.