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Controlling the uniformity and morphology of graphene grown on the C-face of SiC is more difficult than on the Si-face. To improve graphene grown on the C-face, a continuous growth process was developed in a conventional tube furnace that included in situ surface preparation by annealing in H 2 followed by an Ar-mediated growth, which was done at a variety of different temperatures and pressures. Optimized H 2 etch conditions for the C-face were developed to improve the starting substrate morphology and reduce the effect of substrate defects on growth. The resulting graphene film, however, had non-uniform thickness due to intrinsic bulk defects within the SiC substrate and an interfacial oxide. Differences between substrate properties, such as polytype, are shown to have a significant effect on growth, with a 4H substrate displaying faster in-plane graphene growth than a 6H substrate. A primarily 2-domain graphene film with significant rotational disorder was found regardless of the starting substrate and growth conditions. Ultra-high vacuum desorption of the interfacial oxide caused the graphene to reorder into a single preferred rotational orientation, suggesting trace oxygen impurities in the growth chamber can play an important role in graphene growth on the C-face of SiC. [ABSTRACT FROM AUTHOR]

Abstract: A polariton-based light emitter is a extraordinary concept as an alternative to a light-emitting diode (LED) or laser diode. The physics of a polariton laser is fundamentally different from the spontaneous emission process of an LED or the inversion and stimulated emission process of a laser diode. The rapid decay and emission from this polariton–exciton state bypasses the normal irreversible spontaneous emission and associated non-radiative decay mechanisms. An AlGaN/AlN nucleation bilayer was employed on -plane sapphire to deposit non-polar GaN quantum wells embedded in an AlGaN-based cavity surrounded by top and bottom distributed Bragg reflectors (DBRs). The reflectance data show that the exciton and photon states can be tuned (by changing the angle of the sample) to the same energy. The characteristic strong coupling was observed in the reflectance data where the states of the exciton and photon do not overlap; rather they split into an upper polariton state and a lower polariton state. The photoluminescence (PL) showed a strong emission at a low stimulation level at a similar energy and angle. [Copyright &y& Elsevier]