Rie Togashi

Abstract The integration of red-green-blue (RGB) light sources is essential for the development of high-resolution micro-light-emitting diode (micro-LED) displays. In this study, we propose a color-tunable device based on self-assembled InGaN-based nanocolumn LEDs without a patterning process. The nanocolumn LEDs exhibited a color shift from red to orange-yellow, pale green, and further to blue as the driving voltage increased. Micro-electroluminescence measurements revealed that a small wavelength shift was observed within individual nanocolumn regions. Instead, emission spots sequentially turned on, transitioning from red to blue (660-435 nm), elucidating the mechanism of color tuning. Combined with pulse-width-modulation driving, these findings open the pathway for the realization of novel monolithic RGB-LED devices.

Herein, triangular‐lattice nanopillar templates are fabricated on sputter‐deposited AlN/Si (111) substrates. Nanotemplate selective‐area growth via radiofrequency‐plasma‐assisted molecular beam epitaxy is employed to grow GaN nanocolumns on the nanopillars. Well‐ordered uniform GaN nanocolumn arrays are obtained by inserting a migration‐enhanced‐epitaxy grown AlN/AlGaN buffer layer, thereby aligning the polarity of GaN to Ga‐polar. Subsequently, bulk InGaN active layers are grown on top of the GaN nanocolumns with increasing growth time (t_g = 10–20 min). In the initial stage of growth (t_g = 10 min), low‐In‐content InGaN grows on the edges of the six‐sided pyramidal top of the GaN nanocolumns. As the growth progresses, low‐In‐composition InGaN fills the sides between InGaN on the edges, while high‐In‐composition InGaN rapidly grows on the top of the c‐plane nanocolumns. High‐angle annular dark‐field scanning transmission electron microscopy reveals the formation of an InGaN core, covered with a low‐In‐composition InGaN shell, on the top of the nanocolumns. At t_g = 20 min, the photoluminescence spectrum exhibits a peak at 669 nm with a full width at half maximum value of 51.7 nm. Thus, the proposed method is suitable for growing red‐light‐emitting well‐ordered InGaN/GaN nanocolumn arrays on Si.

Abstract In this paper, we report achieving extremely high-density packing in high-voltage vertical gallium nitride (GaN) nanocolumn Schottky barrier diodes (NC-SBDs) through the adoption of a bottom-up process. The NC-SBDs were formed via epitaxial growth using Titanium-mask selective area growth (Ti-SAG) by rf-plasma-assisted MBE (rf-MBE), realizing a packing density equivalent to exceeding 10 million columns/mm². Our fabricated NC-SBDs with a period of 300 nm, a diameter of 250 nm, and a drift length of 1.3 μm demonstrated a breakdown voltage (BV) of 260 V with an on-resistance of 2.0 mΩcm², yielding an excellent figure of merit of 33.8 MW/cm² for nanocolumn-based high-voltage devices. We also discuss dielectric reduced surface field effect and impurities within the nanocolumns as potential factors contributing to the achievement of higher BV devices.