HIGH DENSITY EXCITATION EFFECTS ON EXCITONS AND ELECTRON-HOLE PAIRS IN AlxGa1-xAs/AlAs QUANTUM WIRES

Abstract

High density excitation effects on excitons in Al x Ga 1-x As/AlAs (x=0.2~0.5) quantum wires (QWRs) have been investigated. In these samples, the difference between the type-I (x≤0.3) and type-II (x≥0.4) band structures was clearly observed in high density effects on the photoluminescence (PL) and its temporal response. In the type-I samples, the PL is characterized by a fast radiative decay process reflecting intra-wire transitions. The PL peak shows a small blueshift with increasing excitation density, and the shift becomes large to 20meV under the highest excitation limit. The large shift is ascribed to intrinsic high density excitation effects appearing beyond the weak localization of the excitons ito structural fluctuations. On the other hand, in the type-II PL, a huge blueshift appears, being much larger than the localization energies of the excitons. This shift is also considered to be due to another intrinsic high-density effects brought about by the long-lived type-II excitons.