Berlin 2008 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 47: GaN: preparation and characterization I
HL 47.8: Vortrag
Donnerstag, 28. Februar 2008, 16:00–16:15, EW 202
Recombination dynamics in coalesced a-plane GaN ELO structures investigated by high spatially and ps-time-resolved cathodoluminescence microscopy — •B. Bastek1, F. Bertram1, J. Christen1, T. Wernicke2, M. Weyers2, and M. Kneissl3 — 1Institute of Experimental Physics, Otto-von-Guericke-University Magdeburg — 2Ferdinand-Braun-Institut für Höchstfrequenztechnik, Berlin — 3Institute of Solid State Physics, Technical University Berlin
The characteristic epitaxial lateral overgrowth (ELO) domains of fully coalesced a-plane GaN layers were directly imaged by highly spatially and spectrally resolved cathodoluminescence microscopy (CL) at 5 K. The patterned layers were grown by MOVPE on r-plane sapphire substrate and stripe masks oriented in the [0110] direction. In the area of coherent growth (I) the broad basal plane stacking fault (BSF) emission centered at 3.41 eV dominates the spectra. Also in the region (II) of coalescence the BSF luminescence dominates, however, the intensity increases by one order of magnitude compared to area (I). In complete contrast, in the stripes associated with the laterally grown domains (III) in [0001] direction, exclusively an intense and sharp (D0,X) emission at 3.475 eV is observed. ps-time-resolved CL of the free excitons (FX) recorded from this domains (III) decays bi-exponentially. The initial lifetime of 180 ps is primarily given by the capture of FX by impurities to form bound excitons (BE). With rising temperature this capture time constant decreases as T−1/4 and reaches a minimum of 104 ps at T = 60 K. Above 60 K, i.e. when FX starts to dominate the BEs, the lifetime increases rapidly to a value of 240 ps for 300 K.