Optical studies of free-standing single InGaAs/GaAs quantum dots

Using electron beam lithography and wet chemical etching we have developed single InGaAs/GaAs quantum dots with diameters between 200 nm and 40 nm. The lithographic definition permits the dot shape as well as the dot size to be controlled. In addition to circular dots, which allow the transition between two- and zero-dimensional systems to be studied, we have fabricated rectangular dots which can be used to study the changeover from one- to zero-dimensional structures. Photoluminescence spectra of the dots show a lateral quantization-induced increase of the bandgap energy as well as emission of higher dot states. The experimental results for the lateral confinement energies can be described well by numerical calculations. The average number of electron-hole pairs in the dot can be derived from different features of the spectre. With decreasing dot diameter we observe a continuous reduction of the luminescence linewidths in our structures. This variation is consistent with a decrease of elastic scattering processes by well widths and compositional fluctuations for reduced dot size.