Excitons, biexcitons, and electron-hole plasma in a narrow 2.8-nm GaAs/AlxGa1-xAs quantum well

We report the use of imaging spectroscopy to study the transition from a bi exciton to a low-density electron-hole plasma inside single quantum dots in a 2.8-nm GaAs/Al0.3Ga0.7As quantum well. Using a 250-nm resolution solid i mmersion microscope to reduce the spatial components of inhomogeneous broad ening, we not only enable studies of single excitons and biexcitons confine d in quantum dots, but also probe electron-hole plasmas bound in the dots a t carrier densities about an order of magnitude lower than what was previou sly reported. The transition from exciton to plasma is found to be a direct result of random capture of excitons in dots, and the observed band-gap re normalization of the plasma agrees with existing theory.