Shuhei Ichikawa 교수

Abstract High-density micro light-emitting diode ( μ -LED) arrays are key to next-generation ultrahigh-resolution displays. As a novel candidate, we report monolithic vertically stacked full-color LEDs consisting of Eu-doped GaN and InGaN quantum wells (QWs). Initially growing Eu-doped GaN, which shows a narrow linewidth ultra-stable red emission, allows vertically stacked growth of subsequent InGaN-QW-based blue/green LEDs while maintaining a high crystal quality. Electroluminescence from full-

A longest carrier lifetime of 33.2 µs was achieved by eliminating the Z1/2 center via thermal oxidation at 1400 °C for 48 h and subsequent surface passivation with a nitrided oxide on a 220-µm-thick n-type 4H-SiC epilayer. By deep-level elimination, photoluminescence (PL) in the infrared region (wavelength: 700–950 nm) was remarkably enhanced at locations of threading dislocations. A threading screw dislocation exhibited much stronger infrared PL than a threading edge dislocation. The present re

Adjusting the growth conditions from those for c-plane growth realizes high-quality semipolar (11¯02) AlGaN/AlN quantum wells (QWs) with atomically smooth surfaces and abrupt interfaces on AlN substrates. Upon comparing the optical properties to those of c-plane QWs using time-integrated and time-resolved photoluminescence spectroscopy, the estimated internal electric field is much smaller in (11¯02) AlGaN/AlN QWs than in c-plane QWs. Thus, (11¯02) AlGaN/AlN QWs have narrower emission line width

In a bulk semiconductor, both threading dislocations (TDs) and point defects (PDs) can act as centers for nonradiative recombination of holes and electrons, but the dominant pathway is not obvious in Al-rich Al${}_{x}$Ga${}_{1\ensuremath{-}x}$N, an ultrawide-band-gap compound that is promising for very efficient emitters in the deep ultraviolet range. This study uses cathodoluminescence and temperature-dependent photoluminescence to clarify the pathway. TDs are clearly visible around 100 K, but

In this work, we fabricate a nitride-based photonic crystal (PhC) nanocavity with an embedded active layer for unexplored red regions using simplified selective wet etching of an ${\mathrm{Al}}_{0.82}{\mathrm{In}}_{0.18}\mathrm{N}$ sacrificial layer. Eu,O-codoped $\mathrm{Ga}\mathrm{N}$ ($\mathrm{Ga}\mathrm{N}$:$\mathrm{Eu}$,$\mathrm{O}$) is embedded in L7-type two-dimensional-PhC (2D-PhC) nanocavities with hexagonal holes. Room-temperature photoluminescence (PL) shows $\mathrm{Eu}$ emission cou

Near-infrared (NIR) light with a wavelength of 650–950 nm is used for various biomedical applications. Although NIR emitters are typically based on GaAs-related materials, they contain toxic elements, and the emission wavelength can easily shift during the device operation due to temperature changes and current injection levels. On the other hand, Tm3+, which is one of the rare-earth ions, can generate ultra-stable NIR luminescence with a wavelength of ∼800nm, based on 3H4–3H6 transitions in a 4

Plasma polymerized polydimethylsiloxane films irradiated under different partial pressures of oxygen with a 172nm vacuum ultraviolet light were investigated in order to clarify the roles of molecular oxygen and photons in photooxidation. The thickness, densities, surface roughness, elemental compositions, and molecular structures of the irradiated and unirradiated films were examined by using glazing incidence x-ray reflectivity, Rutherford backscattering, infrared, and x-ray absorption (XAS) sp

The trivalent terbium ion (Tb3+) emits ultra-stable visible light consisting of blue, green, yellow, and red. Tb-doped semiconductors are candidates for novel full-color light sources in next-generation displays. Particularly, Tb-doped AlxGa1−xN (AlxGa1−xN:Tb) has attracted much attention for device applications. We present the luminescence properties of AlxGa1−xN:Tb grown by the organometallic vapor phase epitaxy. At 15 K, emission related to the 5D4–7FJ (J = 3, 4, 5, 6) transitions is observed