We demonstrate the monolithic integration of green and orange InGaN-based nanocolumn light-emitting diodes (LEDs). Four nanocolumn LED crystals (LEDs 1 to 4), which consisted of regularly arranged InGaN-based nanocolumns in a triangular lattice of 400 nm lattice constant, were grown on the same GaN template on a (0001) sapphire substrate, with designed nanocolumn diameters D of 150, 190, 230, and 270 nm for LEDs 1–4, respectively. LEDs 1 to 3 operated under DC current injection at room temperature, emitting at 544, 583, and 597 nm, respectively. This experiment paves the way for the monolithic integration of three-primary-color nanocolumn LEDs.

The valacyclovir and prednisolone therapy was more effective in treating Bell's palsy, excluding zoster sine herpete, than the conventional prednisolone therapy. To our knowledge, this is the first controlled study of an antiviral agent in the treatment of a sufficient number of Bell's palsy cases based on an etiologic background.

Two-dimensional (2D) light diffraction in a uniform array of GaN nanocolumns arranged in a rectangular lattice dramatically enhanced the light intensity at a specific wavelength, indicating the function of 2D distributed feedback (DFB). Here a GaN rectangular-lattice nanocolumn array, which integrated InGaN/GaN multiple quantum wells (MQWs) in the top region of the nanocolumns, was grown by rf-plasma-assisted molecular beam epitaxy (rf-MBE). At a specific wavelength of 471.1 nm, the first observation of stimulated emission from 2D-DFB in an InGaN-based nanocolumn array was obtained. The specific wavelength is calculated by the 2D finite-difference time domain (2D-FDTD) method on the assumption of a refractive index dispersion of GaN; a simple expression for specific wavelength, which is a function of the array period L and the hexagon side length S of each nanocolumn, is proposed, which is convenient for producing a simple design of a GaN nanocolumn array structure in a square lattice.

The monolithic integration of four-colour indium gallium nitride (InGaN)-based nanocolumn light-emitting diodes (LEDs) is demonstrated. In the integrated nanocolumn LED unit, blue-, sky-blue-, green-and yellow-emitting micro-LEDs (LEDs 1-4) with a 65 μm diameter circular indium tin oxide emission window were arrayed in a 2 × 2 square lattice with a lattice constant of 190 μm. LEDs 1-4 consisted of nanocolumn arrays arranged in a triangular lattice with a lattice constant of 300 nm and their nanocolumn diameters at the position of the InGaN/gallium nitride (GaN) multiple quantum wells (MQWs) were 119, 145, 188 and 231 nm, respectively. The increase in nanocolumn diameter from LED 1 to LED 4 resulted in increasing emission peak wavelengths, which were 465, 489, 510 and 570 nm for LEDs 1-4, respectively. On the same substrate, a red-emitting micro-LED was prepared, in which the nanocolumn diameter was increased to 260 nm by using a 350 nm-lattice-constant nanocolumn array. A combination of different lattice constants in an integrated LED unit is expected to contribute to the achievement of red-green-blueyellow (RGBY)-colour-integrated nanocolumn LEDs.Introduction: Light emitters based on a novel concept, in which microscale light-emitting diodes (LEDs) with various emission colours such as red, green, blue and yellow (RGBY) are monolithically integrated [1], will enable the application of LEDs to full-colour displays and solidstate lighting by providing high functionality and high colour rendering. Indium gallium nitride (InGaN)-based LEDs, which can emit light in the entire visible range from blue to red [2], are the most attractive candidate for developing such integrated micro-LEDs. However, using InGaNfilm-based LEDs, the luminous efficiency degrades markedly from green to red [2] and hybrid integration is a standard means of assembling LEDs with different emission colours. Meanwhile, gallium nitride (GaN) nanocolumns are one-dimensional columnar nanocrystals [3,4] having a low dislocation density and a strain relaxation effect [5][6][7]. Thus, they are expected to contribute to efficient RGBY emissions from InGaN. Furthermore, the emission colour of InGaN/GaN-based nanocolumn arrays can be controlled via the diameter and period of the nanocolumn arrays [8]. Recently, on the basis of this emissioncolour control scheme, monolithic integration of InGaN-based nanocolumn LEDs with green and orange emissions has been demonstrated [1]. In the work reported in this Letter, we have achieved monolithic integration of four-colour (blue, sky-blue, green and yellow) InGaN-based nanocolumn LEDs, in which micro-LEDs with a 65 μm diameter circular emission area were arrayed in a 2 × 2 square lattice with a lattice constant of 190 μm.

Stimulated emission with very low threshold excitation power density was observed for GaN nanocolumns grown on (0001) sapphire substrate by RF-plasma assisted molecular beam epitaxy. The photopump measurements were carried out under 355 nm Nd : YAG laser excitation with the surface emission configuration. The threshold excitation power density was 198 kW/cm 2 at room temperature. The peak wavelength shifted from 370.2 to 370.9 nm when increasing the excitation power from 130 to 440 kW/cm 2 . The peak intensity increased nonlinearly with excitation power. For the lower excitation condition using a 325 nm He -Cd laser, the spontaneous emission peak was observed at 363.2 nm and the intensity was 20~30 times stronger than for a 3.7 µm-thick MOCVD-grown GaN film with a dislocation density of 3~5 × 10 9 cm -2 . With this configuration the peak intensity was increased propotionally with excitation power. These results indicate that GaN nanocolumns have high potential to realize high performance optical devices.