Plasmonic effects in metal/semiconductor composites have recently received a lot of attention. Many exciting applications of them are expected for light amplification and conversion. To reveal optical peculiarities of InN related to plasmonic resonances, a comparative study has been performed of the films grown by MBE (i) with obvious inclusions of metallic indium, (ii) without the massive inclusions, and (iii) with intentionally formed sheets of the metallic nano-particles. Additionally, thin In insertions (10-50 nm) in a GaN matrix have been fabricated to study interband absorption in metallic In, whose onset occurs near 0.7 eV. In the first type of InN-based structures, the spectra of thermally detected optical absorption (TDOA) measured at 0.35 K show pronounced peaks near 1 eV, ascribed to the Mie resonances. Emission intensity is strongly enhanced in the vicinity of the metallic inclusions. This phenomenon is discussed in terms of coupling of radiative states with the surface plasmons. In the state-of-art InN films grown outwardly without such inclusions, the TDOA spectra also exhibit a sharp peak, but near 0.7-0.75 eV. Theoretical estimation shows that this peak position may correspond to the surface plasmons in an InN composite with thin oblate metallic insertions. Generally, the optical properties of such films are similar to those of the layers with the intentionally introduced sheets of the In nano-particles. In both types of structures, PL excitation spectra have pronounced peaks in the same 0.7-0.75 eV range, as in the TDOA. The emission is strongly p-polarized with the degree of polarization as much as 40%. PL intensity is increased when exciting at higher angles to the surface normal. The emission in InN frequently consists of two peaks. The origin of the PL splitting is considered taking into account different states involved into recombination process and their coupling with plasmonic modes.

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1. InN/In nanocomposites: plasmonic effects and optical properties