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HL: Fachverband Halbleiterphysik

HL 45: Group-III-Nitrides: Optical Properties II

HL 45.12: Vortrag

Mittwoch, 24. März 2010, 17:30–17:45, H15

Broadening mechanism of excitonic transitions in GaN nanowire ensembles — •Carsten Pfüller, Oliver Brandt, Caroline Chèze, Lutz Geelhaar, and Henning Riechert — Paul-Drude-Institut für Festkörperelektronik, Berlin, Germany

Nanowires (NWs) offer the possibility to integrate III/V and II/IV semiconductors of high crystalline quality even on lattice mismatched substrates such as silicon.

We investigate the photoluminescence (PL) of GaN NWs grown by plasma-assisted molecular beam epitaxy on a Si(111) substrate. The energy of the donor-bound exciton emission at 3.472 eV confirms the NWs to be unstrained. Its linewidth is typically of the order of 3 meV, which is much broader than expected for a strain-free semiconductor.

PL spectra of single NWs dispersed onto a Si(111) vary widely from wire to wire and differ significantly from ensemble spectra. While the majority of dispersed NWs experiences strain from interaction with the substrate, a few NWs exhibit sharper excitonic lines than the ensemble. These lines comprise the donor-bound exciton and free exciton emission of strainfree GaN as well as a set of sharp transitions at 3.475-3.476 eV. The same transitions are observed for as-grown, low density NW ensembles. We attribute these high-energy lines to recombination of excitons bound to surface donors. The statistically distributed distances of these donors to the surface determines the spectral energy of the related exciton recombination and thus provide a natural explanation for the unusual broad luminescence of the unstrained NW ensemble.