Near-field optical imaging and spectroscopy of a coupled quantum wire-dot structure - art. no. 155316

A coupled GaAs/AlGaAs quantum wire (QWR)-dot sample grown by molecular beam epitaxy on a patterned (311)A GaAs substrate is studied by near-field spec troscopy at a temperature of 10 K with a spectral resolution of 100 mu eV. The two-dimensional potential energy profiles of the sample including local ized excitonic states caused by structural disorder are determined in photo luminescence measurements with a spatial resolution of 150 nm. One finds a potential barrier of 20 meV between the quantum wire and the embedding quan tum well (QW) on the mesa top of the structure. This is due to local thinni ng of the GaAs layer. In contrast, the wire-dot interface results free of e nergy barriers. The spatial variation of the GaAs layer thickness provides information on the growth mechanism determined by lateral diffusion of Ga a toms which is modeled by an analytical model. By performing spatially resol ved photoluminescence excitation measurements on this wire-dot structure, w e present a method for investigating carrier transport in low-dimensional s ystems: The dot area is used as an optical marker for excitonic diffusion v ia QW and QWR states. The two-dimensional (2D) and 1D diffusion coefficient s are extracted as a function of the temperature and discussed.