Robin Nicholas

Abstract:

We report measurements of photoluminescence (PL) from self-assembled InSb quantum dots (QD's) grown by metal-organic vapor-phase epitaxy in a matrix of GaSb as a function of excitation power, temperature, and magnetic field. PL is observed in the region 1.7-1.8 μm from InSb quantum dots. For low excitation power the PL is dominated by the lowest quantum dot transition energy. When the excitation power is increased the quantum dot transition increases in energy by ∼ 11 meV, and further transitions are observed from the wetting layer, bulk acceptor, and free excitons. Magneto-PL is used to calculate the in-plane dot confinement energies by fitting the data to the ground state of a Fock-Darwin set of energy levels. The in-plane confinement energy deduced increases from ∼6 to ∼18 meV as the excitation power is increased. This is similar to the increase in the quantum dot transition energy, and suggests that this is due to a progressive population of a distribution of strongly communicating dots with decreasing lateral sizes. Further support for this picture comes from the temperature dependence of the quantum dot transition energy, which is also found to increase by a relatively similar amount as the temperature is raised from 11 to 50 K, following a correction for the temperature dependence of the bulk energy band gaps.

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.