Photoluminescence (PL) mapping was conducted to elucidate the detailed mechanism of PL enhancement based on energy transfer from excitons to surface plasmon polariton (SPP) observed in silver coated InGaN quantum wells (QWs)[1]. Moreover, recently we reported that the photo-absorption efficiency was also remarkably increased by using Al film [2]. In order to understand the enhancement mechanism, here we measured the microscopic PL mapping.
50-nm-thick of Ag films were deposited onto half part of blue emitting InGaN/GaN QWs with 3-nm-thick InGaN layers which have green emissions. PL spectra mappings were measured by using a fluorescence microscope with a mercury lump for excitation. The moving stage was electrically controlled by a stepping motor with 1 µm step.
Fig. 1(a) and (b) show the PL peak intensity and the peak wavelength mapping images obtained from metal un-coated part of InGaN QW, respectively. Both of PL peak intensity and peak wavelength values showed some spatial fluctuation in scanned area. The regions with higher PL intensity seem to have longer PL wavelength. This positive correlation between the PL intensities and peak wavelength should be due to the exciton localization effect in emission layer.Fig. 1(c) and (d) show the PL peak intensity and the peak wavelength mapping images obtained from silver coated part of InGaN QW, respectively. In this case the positive correlation was completely disappeared.
PL enhancement by SP on silver film was confirmed to be accompanied with energy transfer from excitons to SPP. If the energy transfer is faster than exciton localization process, the positive correlation can be cancelled. From above, we considered that the positive correlation disappearance suggest the energy transfer from excitons to SPP should be much faster than the exciton localization. Details will be discussed at the conference.
[1] K. Okamoto, I. Niki, A. Shvartser, and Y. Narukawa, Nat. Mater. 3, 601 (2004).
[2] K. Tateishi, M. Funato, Y. Kawakami, K. Okamoto, and K. Tamada, Appl. Phys. Lett. 106, 121112 (2015).
Photonic & plasmonic nanomaterials , Optical properties of nanostructures
