P. B. Joyce

Surface morphology evolution during the overgrowth of large InAs–GaAs quantum dots

The effects of GaAs overgrowth on the structural properties of large low-growth-rate InAs quantum dots (LGR-QDs) grown on GaAs(001) are examined using in situ scanning tunneling microscopy. Strongly anisotropic surface diffusion produces a characteristic valley-ridge structure above the LGR-QDs and the surface is not planarized even after a cap thickness >400 A. The evolution of surface morphology proceeds very differently to the case of smaller conventional growth rate QDs capped under the same conditions, due to the different initial strain states of the QDs.

Photoluminescence characterization of InAs/GaAs quantum dot bilayers

Abstract We have investigated the emission from InAs/GaAs quantum dots (QD) bilayer samples with different GaAs spacer thickness. For large spacers, one peak is observed, and the layers are independent. For small spacers, one peak is observed and the layers are then electronically coupled. For intermediate spacers (≈120 A), two emission peaks are observed and these can be made coincident by tuning the amount of InAs deposited in the second layer. We present a technique using two different excitation wavelengths, which enables us to attribute the emission to each layer, and to show that the shifts are not due to electronic coupling. Moreover, resonant excitation shows that the wetting layers are also different in each layer. These results indicate that the presence of the first QD layer strongly influences the growth of the second one, leading to very different properties.

Nucleation and growth of InAs quantum dots on GaAs[001]

The formation of dislocation-free quantum dots (QDs) in material systems such as InAs/GaAs has attracted great interest because of the novel optoelectronic properties of QDs and their potential uses for device applications. However, some fundamental aspects of QD formation such as the exact nature of the 2D-3D growth mode transition at the critical coverage (/spl theta//sub crit/) remain poorly understood. Our detailed scanning tunneling microscopy (STM) studies of InAs/GaAs[001] growth as a function of InAs coverage (/spl theta/) provide the first direct evidence for the existence of small 3D precursors in QD formation. Scaling analysis of QD size distributions shows that strain is only a significant factor in the initial stages of QD growth. These results are in disagreement with previous studies of InAs/GaAs[001] QD growth.