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Abstract:

We report a study of novel structures in which an InSb quantum dot (QD) layer in GaSb is coupled to a nearby narrow InAs quantum well (QW). Magnetic fields have been used to probe the photoluminescence (PL) of the dots and the wells separately and in the coupled structures. We have found that the introduction of the dot-well coupling leads to a dramatic suppression of the diamagnetic shift of the exciton when the magnetic field is oriented parallel to the well plane. The observed shift is 1-2 meV with an applied field of 17 T. In contrast, when the field is perpendicular to the layer plane, there is little difference in the response of the coupled structures compared to that of the quantum wells on their own, suggesting that the behaviour is dominated by the motion of the electrons in the wells.

Abstract:

We perform local anodic oxidation (LAO) on III-V semiconductor surfaces with the help of an atomic force microscope (AFM). Regular arrays of oxide dots are created by applying a voltage in the range 10-20 V to a conducting tip. We succeed in drawing dots with diameters of 30nm or less and heights of 4-6nm, allowing for lattice periods as small as 75nm. With an anodisation time of 100-250ms per dot, the creation of large patterns is possible provided the drift of the instrument is corrected for.

Abstract:

Thermodynamic arguments are presented for the formation of atomic order in heteroepitaxially grown semiconductor quantum dots. From thermodynamics several significant properties of these systems can be derived, such as an enhanced critical temperature of the disorder-order transition, the possible co-existence of differently ordered domains of varying size and orientation, the possible existence of structures that have not been observed before in semiconductors, the occurrence of atomic order over time, and the occurrence of short range order when the growth proceeds at low temperatures. Transmission electron microscopy results support these predictions. Finally, we speculate on the cause for the observed increase in life time of (In, Ga)As/GaAs quantum dot lasers [H-Y. Liu et al., Appl. Phys. Lett. 79, 2868 (2001)].