STRUCTURAL AND OPTICAL-PROPERTIES OF INAS-GAAS QUANTUM DOTS SUBJECTEDTO HIGH-TEMPERATURE ANNEALING

Annealing at higher temperature (700 degrees C) of structures with two -dimensional and three-dimensional arrays in InAs-GaAs quantum dots (Q Ds) results in an increase in the size and in a corresponding decrease in the indium composition of the QDs. The change in the In compositio n is monitored by the contrast pattern in the plan-view transmission e lectron microscopy (TEM) images viewed under the strong beam imaging c onditions. Increase in the size of the QDs is manifested by the plan-v iew TEM images taken under [001] zone axis illumination as well as by the cross-section TEM images, We show that the dots maintain their geo metrical shape upon annealing. Luminescence spectra demonstrate a shif t of the QD luminescence peak toward higher energies with an increase in the annealing time (10-60 min) in agreement with the decrease in in dium composition revealed in TEM studies. The corresponding decrease i n the QD localization energy results in an effective evaporation of ca rriers from QDs at room temperature, and the: intensity of the QD lumi nescence decreases, and the intensity of the wetting layer and the GaA s matrix luminescence increase with the increase in the annealing time . (C) 1996 American Institute of Physics.