Spatially resolved inhomogeneous depressions of the excitons Zeeman splitting in an integrated magnetic-multiple quantum wells system

We report on the generation of a nonuniform spatial distribution of the heavy and light-hole excitons in a multiple quantum wells system integrated with a localized inhomogeneous weak magnetic field. An inhomogeneous spatially resolved depression of the Zeeman splittings of the heavy-hole excitons and the light-hole excitons with respect to their translational wave vectors is observed. A localized inverted concentration of the two types of the excitons due to the inhomogeneity of the magnetic field is also measured. A simple method to integrate permanent magnetic materials with the multiple quantum wells system is used to create an accessible degree of control for magnetically manipulating the excitonic distribution

Quantum Efficiency Enhancement Depending on the Thickness of p-GaN Spacer Layer in Localized Surface Plasmon-Enhanced Near-Ultraviolet Light-Emitting Diodes by Using Colloidal Silver Nanoparticles

We demonstrated the dependence on thickness of p-GaN spacer layer in the localized surface plasmons (LSPs)-enhanced near-ultraviolet light-emitting diodes (NUV-LEDs) by pneumatic spray process using colloidal silver (Ag) nanoparticles (NPs). The LSPs-enhanced NUV-LEDs with 10- and 20-nm-thick p-GaN spacer layer showed enhanced internal quantum efficiency (IQE) and reduced effective exciton lifetime by introducing the colloidal Ag NPs. The IQE of LSPs-enhanced NUV-LEDs with 10- and 20-nm-thick p-GaN spacer layer was increased by 18.8% and 24.2%, respectively. These results indicate that the spontaneous emission rate is increased by LSPs-excitons resonant coupling. However, the NUV-LEDs with 40- and 100-nm-thick p-GaN spacer layer showed decreased IQE and extended exciton lifetime due to the evanescent wave property of LSPs field from colloidal Ag NPs. © The Author(s) 2019. Published by ECS..1

Microscopic Observation of Low Efficiency in Green Light-Emitting Diodes

The low efficiency of green light-emitting diodes (LEDs), a phenomenon known as the green gap, is a key obstacle hindering the application of LEDs as next-generation light sources to pioneer a plethora of new applications in the optical, medical, and communication sectors. Based on a microscopic photoluminescence analysis of green GaN-based multiple quantum wells, we find that In-enriched emission clusters on the submicrometer scale, previously thought to be efficient luminescent centers, do not emit light effectively. Such emission clusters can localize an excessively large amount of carriers, leading to the subsequent occurrence of vigorous nonradiative recombination processes. We also observe that the effective volume of the LED active region is significantly reduced, possibly because the generation of these In-enriched clusters via metastable phase separation significantly degrades the surrounding crystal quality. The microscopic analysis of luminescent clusters gives insight into the low efficiency of green LEDs, which may guide future directions for the development of LEDs

Note: Automatic laser-to-optical-fiber coupling system based on monitoring of Raman scattering signal

We developed an automatic laser-to-optical-fiber coupling (ALOC) system that is based on the difference in the Raman scattering signals of the core and cladding of the optical fiber. This system can be easily applied to all fields of fiber optics since it can perform automatic optical coupling within a few seconds regardless of the core size or the condition of the output end of the optical fiber. The coupling time for a commercial single-mode fiber for a wavelength of 632.8 nm (core diameter: 9 mu m, cladding diameter: 125 mu m) is similar to 1.5 s. The ALOC system was successfully applied to single-mode-fiber Raman endoscopy for the measurement of the Raman spectrum of carbon nanotubes

Time-Resolved Ultraviolet Near-Field Scanning Optical Microscope for Characterizing Photoluminescence Lifetime of Light-Emitting Devices

We developed a instrument consisting of an ultraviolet (UV) near-field scanning optical microscope (NSOM) combined with time-correlated single photon counting, which allows efficient observation of temporal dynamics of near-field photoluminescence (PL) down to the sub-wavelength scale. The developed time-resolved UV NSOM system showed a spatial resolution of 110 nm and a temporal resolution of 130 ps in the optical signal. The proposed microscope system was successfully demonstrated by characterizing the near-field PL lifetime of InGaN/GaN multiple quantum wells