09:00 〜 09:30
▲ [13a-2C-1] [JSAP-OSA Joint Symposia 2015 Invited Talk] New Development of Plasmonics Towards High-Efficiency Light-Emitting Devices
キーワード：plasmonics,LED,InGaN
In 2004, we reported for the first time that the photoluminescence (PL) from InGaN/GaN quantum wells (QW) was highly enhanced by the surface plasmon (SP) resonance on Ag thin films based on the improvement of the internal quantum efficiency (IQE). By using this technique, high-efficiency light emission is predicted even by electrically pumping as well as photo pumping. I present here the recent progress of our approach toward development of the high-efficiency plasmonic LED devices.
We found huge Purcell enhancement factors (~500) of the radiative recombination rates of excitons by the SP resonance. This hyper enhanced spontaneous emission increases the IQEs almost 100% at the best matched wavelength. This suggests that super bright LEDs which have perfect efficiencies at any wavelength should be achievable by strict control of the SP frequency.
We also obtained the enhancement of the electroluminescence from the fabricated plasmonic LED device structure by employing the very thin p+GaN layer. The distance between the QW and the Ag interface of this structure was 23 nm. The enhancement ratio was 2-fold in this moment, but we believe that further enhancement should be available by optimization of the metal and device structures.
We succeeded to control the SP resonance within visible wavelength region by using the various metal nanostructures such as metal nano-grains and nano-sheets. Next important challenge is extension of the SP resonance into UV or IR wavelength regions for wider applications. To extend plasmonic tuning into deep UV regions, Al should be useful because the SP resonance frequency of Al is located at ~200nm. We succeeded the enhancements of deep UV (~250nm) light emissions from AlGaN/AlN-based QWs with Al coating. Moreover, we obtained unexpectedly large enhancement for green emissions from InGaN/GaN using Al film. This result would provide us the high-efficiency green LED which has been very difficult to develop despite its importance.
On the other hand, to extend plasmonics into IR wavelength region has been very difficult because the many kinds of metals have large dumping factors of the dielectric constants at the IR regions. We checked the optical properties of many metals and found that only a few metals have a potential to use for IR plasmonics. For example, we calculated the localized SP resonance spectra of Tantalum (Ta) nanoparticles by the FDTD method and obtained clear peaks at the near-IR regions.
The methods presented here to tune the SP resonance over the UV-IR range should bring new possibilities of applications to plasmonics. We believe that our approach of device applications based on broadband plasmonic resonance would lead to new class of several photonic and electronic technologies.
We found huge Purcell enhancement factors (~500) of the radiative recombination rates of excitons by the SP resonance. This hyper enhanced spontaneous emission increases the IQEs almost 100% at the best matched wavelength. This suggests that super bright LEDs which have perfect efficiencies at any wavelength should be achievable by strict control of the SP frequency.
We also obtained the enhancement of the electroluminescence from the fabricated plasmonic LED device structure by employing the very thin p+GaN layer. The distance between the QW and the Ag interface of this structure was 23 nm. The enhancement ratio was 2-fold in this moment, but we believe that further enhancement should be available by optimization of the metal and device structures.
We succeeded to control the SP resonance within visible wavelength region by using the various metal nanostructures such as metal nano-grains and nano-sheets. Next important challenge is extension of the SP resonance into UV or IR wavelength regions for wider applications. To extend plasmonic tuning into deep UV regions, Al should be useful because the SP resonance frequency of Al is located at ~200nm. We succeeded the enhancements of deep UV (~250nm) light emissions from AlGaN/AlN-based QWs with Al coating. Moreover, we obtained unexpectedly large enhancement for green emissions from InGaN/GaN using Al film. This result would provide us the high-efficiency green LED which has been very difficult to develop despite its importance.
On the other hand, to extend plasmonics into IR wavelength region has been very difficult because the many kinds of metals have large dumping factors of the dielectric constants at the IR regions. We checked the optical properties of many metals and found that only a few metals have a potential to use for IR plasmonics. For example, we calculated the localized SP resonance spectra of Tantalum (Ta) nanoparticles by the FDTD method and obtained clear peaks at the near-IR regions.
The methods presented here to tune the SP resonance over the UV-IR range should bring new possibilities of applications to plasmonics. We believe that our approach of device applications based on broadband plasmonic resonance would lead to new class of several photonic and electronic technologies.