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Optical and local current studies on InAs/GaAs quantum dots

By optimizing the growth technique of molecular beam epitaxy (MBE), we've prepared high quality InAs quantum dot samples, with high density (up to 1.2 x 1011 cm-2) and highly homogeneous size. Strong room temperature photoluminescence (PL) have been observed. The PL study reveals four confined-states QD transitions, which shows filling effect of the excited states. Dependence of these recombinations on excitation intensity and temperature has also been investigated. Conductive atomic force microscopy (C-AFM) has been used to probe the local current of InAs surface quantum dots (SQDs) on doped GaAs layer. It is found that current about picoampere can be drawn from individual QD while bias of a few hundred mV is applied between tip and the sample. Further I-V studies discover that surface quantum dots usually has a threshold bias near 200 mV for current transmission, whereas bias of 400 mV is needed when the conductive tip is located on wetting layer.