Photoluminescence from GaAs/AlGaAs quantum wires and quantum dots

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Abstract
Quantum wires and dots have been fabricated by local interdiffusion of undoped GaAs/AlGaAs quantum well structures. Thermal interdiffusion is induced by a focused laser beam. In periodic arrays of quantum wires the photoluminescence (PL) splitts into several predominant lines which are separated by up to about 8meV. These PL lines are attributed to the quantum number conserving optical transitions between 1-dimensional electron and hole levels. Sample inhomogeneities cause broadening of the lines. The transition peaks shift in energy scanning a PL probe with a size of only one micron across the structures. Inhomogeneous line broadening is eliminated by investigation of a single quantum dot. A series of dots with different size show a systematic behaviour of PL blueshift and PL peak splitting. The main peaks in PL and PL excitation (PLE) spectra coincide well in energy and they are separated by up to about 10meV. These peaks can be described by the allowed transitions between 0D single particle levels within the nearly parabolic potentials caused by interdiffusion. Detailed calculations of excitonic states within the structures result in similar optical spectra. The observation of intense luminescence from excited dot levels indicates a slowing down of the energy relaxation of carriers. This is in good agreement with calculated LA phonon emission rates of carriers in 0D systems. At low excitation density PL lines from a single quantum dot reveal widths of less than 0.5meV

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