Berlin 2012 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 64: GaN: Preparation and Characterization III

HL 64.3: Talk

Wednesday, March 28, 2012, 17:00–17:15, EW 202

In-situ Measurements and X-ray Diffraction of AlInN/AlGaN Distributed Bragg Reflectors — •Christoph Berger, Jürgen Bläsing, Armin Dadgar, Alexander Franke, Thomas Hempel, Jürgen Christen, and Alois Krost — Otto-von-Guericke-Universität Magdeburg

We report on the MOVPE-growth of lattice-matched Al_0.85In_0.15N/
Al_0.2Ga_0.8N distributed Bragg reflectors (DBRs) with up to 45 layer pairs. These DBRs are suited as bottom mirrors in GaN-based microcavities for the realization of vertical cavity surface emitting lasers or even polariton lasers, which are working in the strong coupling regime. For the latter high Q-factors of the microcavities are prerequisite, thus the mirrors need to exhibit reflectivities above 99 %. To achieve such values, a high number of mirror pairs is required. Thus, the structures become vulnerable to relaxation processes or crack formation. Furthermore, the mirrors have to be laterally and vertically homogeneous with smooth interfaces. To evaluate the strain-state and the smoothness already during growth, the process was monitored by in-situ curvature and reflectance measurements. Subsequently, the Bragg reflectors were investigated by different methods of X-ray diffraction (XRD). This included high resolution XRD, asymmetrical reciprocal space mapping, as well as experiments under grazing incidence and in transmission geometry. From these various measurements, it could be ascertained that the crack-free structures are grown fully strained and possess a high structural and optical quality, enabling reflectivities of 99 % in the near UV region.