STRUCTURAL AND OPTICAL-PROPERTIES OF SELF-ASSEMBLED INGAAS QUANTUM DOTS

A one step method for the production of quantum dots is presented. The method exploits the mismatch strain of molecular beam epitaxy (MBE) deposited InGaAs on GaAs to induce a transition from the two-dimensional growth mode to the three-dimensional (Stranski-Krastanow) growth mode. The cluster size is limited to quantum dimensions by precisely controlling the amount of InGaAs that is deposited in order to cause the growth mode transition. Very narrow lateral size distributions with standard deviations of 14% on the dot area have been obtained. Smooth MBE growth of GaAs over these clusters produces a layer of quantum dots, whose high quality and uniformity has been observed with transmission electron microscopy, atomic force microscopy, and photoluminescence (PL). The quantum dot PL intensity is enhanced compared to a reference quantum well. Resonances in photoluminescence excitation (PLE) spectra suggest that the density of states in these dots has minima close to zero between the quantum states, as expected for a zero-dimensional system These PLE peaks shift with the detecting energy, showing that by changing the detecting energy, we are sampling different sizes of dots. The temperature dependence of the PL indicates that the onset energy of thermal quenching of quantum dots is enhanced by a factor of 2, as compared to a quantum well, due to the additional confinement. In all samples, there is virtually no overlap between the PL emission and the first PLE peak of the quantum dots.