Robin Nicholas

Abstract:

We report a study of the vertical transport of short-period InAs GaSb supertattices in high parallel magnetic fields. At low magnetic field. the current-voltage characteristic exhibits a double negative differential conductance feature. We attribute the first peak to Esaki-Tsu miniband conduction and the repeat feature to LO-phonon-assisted miniband tunnelling, At high magnetic fields, in the quantum limit we observe a series of conductance peaks that satisfy the Stark-cyclotron-resonance condition. At the magnetophonon condition there is a significant enhancement of these peaks We explain these observations in terms of the strong k dependence of the miniband width. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract:

Low-temperature photoluminescence studies of InSb/GaSb quantum dots strongly coupled to narrow InAs quantum wells are presented. Inclusion of the quantum well has enabled the dot emission energy to be reduced from 0.72 to 0.48 eV. Four-band k.p calculations have been used to illustrate the proposed mechanism. In particular, the importance of the InAs well width and GaSb 'spacer' thickness is discussed in terms of the overall character of the coupled state and the relative intensity of the transition. (C) 2002 Elsevier Science B.V. All rights reserved.

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/GaS quantum dot lasers [H-Y. Liu et al., Appl. Phys. Lett. 79,2868 (2001)].