We investigated experimentally and theoretically the valence-band structure of wurtzite InP nanowires. The wurtzite phase, which usually is not stable for III-V phosphide compounds, has been observed in InP nanowires. We present results on the electronic properties of these nanowires using the photoluminescence excitation technique. Spectra from an ensemble of nanowires show three clear absorption edges separated by 44 meV and 143 meV, respectively. The band edges are attributed to excitonic absorptions involving three distinct valence-bands labeled: A, B, and C. Theoretical results based on "ab initio" calculation gives corresponding valence-band energy separations of 50 meV and 200 meV, respectively, which are in good agreement with the experimental results.

We investigated the optical emission at 2 K from InP quantum dots (QDs) grown on GaAs with and without a GaAs capping layer. Uncapped QDs present relatively long emission decay times (4–14 ns). In contrast, dots covered with a GaAs layer present much shorter lifetimes (∼1 ns). We analyse those results considering the effects of surface states (non-radiative recombination channel) and intermixing at the interfaces (affecting the electron–hole wave-function overlap). The continuous-wave optical emission spectrum from uncapped dots does not reproduce straightforwardly the dot size distributions obtained by atomic force microscopy measurements, showing an enhancement of the emission from small dots. The result is attributed to the strong dependence of the electron–hole wave-function overlap with the dot size obtained by our calculations.

We performed a detailed investigation of the structural and optical properties of multi-layers of InP/GaAs quantum dots, which present a type II interface arrangement. Transmission electronic microscopy analysis has revealed relatively large dots that coalesce forming so-called quantum posts when the GaAs layer between the InP layers is thin. We observed that the structural properties and morphology affect the resulting radiative lifetime of the carriers in our systems. The carrier lifetimes are relatively long, as expected for type II systems, as compared to those observed for single layer InP/GaAs quantum dots. The interface intermixing effect has been pointed out as a limiting factor for obtaining an effective spatial separation of electrons and holes in the case of single layer InP/GaAs quantum-dot samples. In the present case this effect seems to be less critical due to the particular carrier wavefunction distribution along the structures.

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