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HL: Fachverband Halbleiterphysik

HL 17: Nitrides: Growth and Characterization

HL 17.8: Vortrag

Montag, 14. März 2011, 16:30–16:45, POT 51

Quantum-Confined Stark Effect Observed in (In,Ga)N/GaN Nanowire Heterostructures — •J. Lähnemann, C. Pfüller, O. Brandt, U. Jahn, E. Luna, T. Flissikowski, L. Schrottke, M. Knelangen, A. Trampert, and H. T. Grahn — Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5–7, 10117 Berlin

Light emitting diodes for the visible spectral region based on planar (In,Ga)N/GaN heterostructures suffer from a high dislocation density and lack of suitable substrates. An alternative is the integration of these heterostructures into nanowires (NWs) grown on Si by molecular beam epitaxy. Indications for the absence of the quantum-confined Stark effect (QCSE) have been reported in the literature, when the piezoelectric polarization is reduced due to an efficient strain relaxation in the NW geometry. In order to elucidate the origin of the observed luminescence centered at 2.4 eV, we combine transmission electron microscopy, cathodoluminescence and micro-photoluminescence (µ-PL) spectroscopy on single NWs. The µ-PL spectra contain a combination of two types of transitions: (i) several sharp lines from localization centers, which are not affected by the excitation power and (ii) a broader band that blueshifts with higher excitation powers. The former are probably related to composition fluctuations in the (In,Ga)N, while the latter is attributed to an inter-well transition between the two 11 nm thick (In,Ga)N insertions separated by an only 2 to 3 nm thick barrier layer. The blueshift under high excitation evidences a screening of the polarization field. Thus, the QCSE appears to be present in these NW heterostructures in contrast to previous reports.