Optical characterization of a InGaN/GaN microcavity with epitaxial AlInN/GaN bottom DBR
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Optical characterization of a InGaN/GaN microcavity with epitaxial AlInN/GaN bottom DBR A. Franke, B. Bastek, S. Sterling, O. August, S. Petzold, P. Veit, J. Christen, P. Moser, M. Wieneke, C. Berger, J. Bläsing, A. Dadgar, and A. Krost Institute of Experimental Physics, Otto-von-Guericke-University Magdeburg, Universitätsplatz 2, 39106 Magdeburg, Germany ABSTRACT Resonant coupling of an optical mode confined within a microcavity and an emitter is the basic prerequisite for the observation of Bose-Einstein condensation phenomena and the development of novel optical devices based on cavity polaritons. We demonstrate highly spatially resolved 2” wafer characterization of the reflectivity and emission properties of a nitride based multi quantum well semi microcavity (i.e. structure without top Bragg reflector) to verify resonant regions. Photoluminescence and reflectivity spectra recorded at the same positions on the wafer exhibit a strong spatial dependence of the multi quantum well emission and the center wavelength of the stop band of the bottom Bragg reflector across the sample. Resonance, i.e., matching of the emission and the center wavelength of the stop band, is found in a region 8 mm off the center of the wafer. The thickness profile across the AlInN/GaN Bragg reflector and multi quantum well layers was obtained by x-ray mappings over the full wafer. A perfect correlation between the local optical properties and the x-ray thickness distribution is found. Additional transmission electron microscopy investigations indicate a complete crack free structure and smooth interfaces between the layers within the Bragg reflector making the structure appropriate for strong coupling applications. INTRODUCTION In last decade several methods for enhancing the outcoupling efficiency of nitride-based light emitting devices were demonstrated [1-4]. One effective way to reduce backside absorption and achieve directional emission is the use of a distributed Bragg reflector (DBR) on the substrate side [4]. Furthermore a new kind of photonic device based on bosonic emission of polaritons could be developed by surrounding the active layer by two highly reflective Bragg reflectors. Thereby the resonant coupling of one selected optical mode within the cavity and the excitons of an active layer leads to the generation of a new kind of quasiparticles named exciton polaritons [5]. Due to their bosonic nature the formation of a Bose condensate (BEC) and furthermore a laser like monochromatic, directional emission without population inversion and low threshold power resulting from the k = 0 state of the dispersion is possible (polariton laser) [6], [7]. BEC as well as polariton lasing was already demonstrated in bulk GaN and GaN quantum well based microcavities (MCs) [8], [9]. Nevertheless polaritonic emission in the visible spectral range by the use of InGaN as active material was not reported so far. Difficulties arise especially from the fabrication of high quality bottom DBRs due to a trade-off between obtaining high crystalline and s
