Nonpolar (11-20) a-GaN/InGaN quantum well (QW) structures were grown by metalorganic chemical vapor deposition on r-plane (1-102) sapphire substrate using a two-stage growth procedure. Our studies demonstrate that, in contrast to polar QWs, these structures show the presence of deep electron traps with activation energy of 0.41 eV in admittance spectra and 1 eV electron traps in capacitance transient spectra. These traps are suspected to be nonradiative recombination centers, decreasing the nonpolar QW photoluminescence (PL) efficiency in our structures compared to polar structures. The PL efficiency of nonpolar QWs is shown to be greatly enhanced by coupling to localized surface plasmons formed by Ag nanoparticles.
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Polyakov et al. (2012) studied this question.
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