Intermediate band solar cells (IBSCs) fabricated to date from In(Ga)As/GaAs quantum dot arrays (QD-IBSC) exhibit a quantum efficiency (QE) that extends to below bandgap energies. However, the production of sub-bandgap photocurrent relies often on the thermal and/or tunneling escape of carriers from the QDs, which is incompatible with preservation of the output voltage. In this work, we test the effectiveness of introducing a thick GaAs spacer in addition to an InAlGaAs strain relief layer (SRL) over the QDs to reduce carrier escape. From an analysis of the QE at different temperatures, it is concluded that escape via tunneling can be completely blocked under short-circuit conditions, and that carriers confined in QDs with an InAlGaAs SRL exhibit a thermal escape activation energy over 100 meV larger than in the case of InAs QDs capped only with GaAs.

Stacked layers of self-assembled In(Ga)As quantum rings on GaAs grown by solid source molecular beam epitaxy are studied by ex situ atomic force microscopy (AFM), low temperature photoluminescence (PL) and cross-sectional transmission electron microscopy (XTEM). The influence of the strain field and InAs segregation on the surface morphology, optical properties and vertical ordering of three quantum ring layers is analyzed for GaAs spacers between layers from 1.5 to 14 nm. AFM and PL results show that samples with spacers $>6\mathrm{nm}$ have surface morphology and optical properties similar to single layers samples. XTEM results on samples with 3 and 6 nm GaAs spacers show that the rings are preserved after capping with GaAs, and evidence the existence of vertically ordered quantum rings.

ZnO microrods were grown by laser assisted flow deposition technique in order to study their luminescence behaviour in the near band edge spectral region. Transmission electron microscopy analysis put in evidence the high crystallinity degree and microrod’s compositional homogeneity. Photoluminescence revealed a dominant 3.31 eV emission. The correlation between this emission and the presence of surface states was investigated by performing plasma treatments with hydrogen and nitrogen. The significant modifications in photoluminescence spectra after the plasma treatments suggest a connexion between the 3.31 eV luminescence and the surface related electronic levels.

The size and emission wavelength of self-assembled $\mathrm{In}\mathrm{As}∕\mathrm{In}\mathrm{P}\left(001\right)$ quantum wires (QWrs) is affected by the $\mathrm{P}∕\mathrm{As}$ exchange process. In this work, we demonstrate by in situ stress measurements that $\mathrm{P}∕\mathrm{As}$ exchange at the $\mathrm{In}\mathrm{As}∕\mathrm{In}\mathrm{P}$ interface depends on the surface reconstruction of the InAs starting surface and its immediate evolution when the arsenic cell is closed. Accordingly, the amount of InP grown on InAs by $\mathrm{P}∕\mathrm{As}$ exchange increases with substrate temperature in a steplike way. These results allow us to engineer the size of the QWr for emission at 1.3 and $1.55\mu \mathrm{m}$ at room temperature by selecting the range of substrate temperatures in which the InP cap layer is grown.