https://purehost.bath.ac.uk/ws/files/9234686/JMS_2011.pdf

A review of reverse osmosis membrane materials for desalination—Development to date and future potential

Light-emitting diodes with emission wavelengths less than 400 nm have been developed using the AlInGaN material system. For devices operating at shorter wavelengths, alloy compositions with a greater aluminium content are required. The material properties of these materials lie on the border between conventional semiconductors and insulators, which adds a degree of complexity to the development of efficient light-emitting devices. A number of technical developments have enabled the fabrication of LEDs based on group three nitrides (III-nitrides) that emit in the UV part of the spectrum, providing useful tools for a wealth of applications in optoelectronic systems.

Ultraviolet light-emitting diodes based on group three nitrides

Over the past decade, advances in LEDs have enabled the potential for wide-scale replacement of traditional lighting with solid-state light sources. If LED performance targets are realized, solid-state lighting will provide significant energy savings, important environmental benefits, and dramatically new ways to utilize and control light. In this paper, we review LED performance targets that are needed to achieve these benefits and highlight some of the remaining technical challenges. We describe recent advances in LED materials and novel device concepts that show promise for realizing the full potential of LED-based white lighting.

LEDs for Solid-State Lighting: Performance Challenges and Recent Advances

In recent years, GaN nanorods are emerging as a very promising novel route toward devices for nano-optoelectronics and nano-photonics. In particular, core-shell light emitting devices are thought to be a breakthrough development in solid state lighting, nanorod based LEDs have many potential advantages as compared to their 2 D thin film counterparts. In this paper, we review the recent developments of GaN nanorod growth, characterization, and related device applications based on GaN nanorods. The initial work on GaN nanorod growth focused on catalyst-assisted and catalyst-free statistical growth. The growth condition and growth mechanisms were extensively investigated and discussed. Doping of GaN nanorods, especially p-doping, was found to significantly influence the morphology of GaN nanorods. The large surface of 3 D GaN nanorods induces new optical and electrical properties, which normally can be neglected in layered structures. Recently, more controlled selective area growth of GaN nanorods was realized using patterned substrates both by metalorganic chemical vapor deposition (MOCVD) and by molecular beam epitaxy (MBE). Advanced structures, for example, photonic crystals and DBRs are meanwhile integrated in GaN nanorod structures. Based on the work of growth and characterization of GaN nanorods, GaN nanoLEDs were reported by several groups with different growth and processing methods. Core/shell nanoLED structures were also demonstrated, which could be potentially useful for future high efficient LED structures. In this paper, we will discuss recent developments in GaN nanorod technology, focusing on the potential advantages, but also discussing problems and open questions, which may impose obstacles during the future development of a GaN nanorod based LED technology.

GaN based nanorods for solid state lighting

The invention provides a laser beam machining method characterized by comprising the steps of mounting a protective tape (25) on the surface (3) of a wafer (1a), radiating laser light (L) by using the back (21) of a wafer (1a) as a laser light incidence plane with an optical converging point (P) positioned in a substrate (15) to thereby form a melt processing region (13) for melt processing by multiphoton absorption, forming, by means of the melt processing region (13), a cutting start region (8) on the side within a predetermined distance from the laser light incidence plane along a predetermined cutting line (5) on the wafer (1a), mounting an expand tape (23) on the back (21) of the wafer (1a), and stretching the expand tape (23) to thereby separate a plurality of chip-like portions (24) from each other that are formed by the wafer (1a) being cut with the cutting start region (8) used as the starting point.

Laser beam machining method

Continuous-wave (CW) operation of nonpolar m-plane InGaN/GaN laser diodes (LDs) with the lasing wavelengths approximately 400 nm was demonstrated. The threshold current was 36 mA (4.0 kA/cm2) for the CW operation [28 mA (3.1 kA/cm2) for pulsed mode], being comparable to that of conventional c-plane violet LDs. Both the LDs with the stripes parallel to a- and c-axes showed TE mode operation, according to the polarization selection rules of the transitions in strained InGaN. The c-axis stripe LDs exhibited lower threshold current density, since the lowest energy transition is allowed. As is the case with the m-plane light emitting diodes fabricated on the free-standing m-plane GaN bulk crystals [Okamoto et al.: Jpn. J. Appl. Phys. 45 (2006) L1197], the LDs shown in this paper did not have distinct dislocations, stacking faults, or macroscopic cracks. Nonpolar m-plane GaN-based materials are coming into general use.

http://iopscience.iop.org/article/10.1143/JJAP.46.L187/pdf

Continuous-Wave Operation of m-Plane InGaN Multiple Quantum Well Laser Diodes

m-Plane (10-10) nonpolar InGaN-based light emitting diodes (LEDs) with no threading dislocations or stacking faults have been realized on m-plane GaN single crystals by conventional metal organic vapor phase epitaxy. The crystalline properties of the material, together with the structures of the LED devices, have been observed by scanning transmission electron microscopy. It is shown that dislocation-free nonpolar nitride layers with smooth surfaces can be obtained under growth conditions involving high V/III ratios, which are the optimized growth conditions for c-plane GaN. The peak wavelength of the electroluminescence emission obtained from the finished devices is 435 nm, which is in the blue region. The output power and the calculated external quantum efficiency are 1.79 mW and 3.1%, respectively, at a driving current of 20 mA.

https://iopscience.iop.org/article/10.1143/JJAP.45.L1197/pdf

Dislocation-Free m-Plane InGaN/GaN Light-Emitting Diodes on m-Plane GaN Single Crystals

Disclosed is a method of manufacturing a semiconductor laser A wafer having a substrate having a semiconductor layer including a light-emitting forming portion epitaxially grown on a surface of the substrate is broken into laser chips having a light-emitting surface at an end face thereof When breaking the wafer into the chips, the breaking at the light-emitting surface is carried out by first forming street grooves in the substrate and thereafter cleaving the light-emitting layer forming portion By doing so, there is no necessity of thinning the substrate to a required extent, facilitating handling during the manufacture process A roughened surface of the street groove is provided in the substrate underlying the light-emitting layer forming portion, which is convenient for irregular reflection of a return light beam often encountered in an optical disc pickup device

Method of manufacturing semiconductor laser

Quantum-confined Stark effects (QCSEs) in a polarization-free m-plane In0.15Ga0.85N∕GaN multiple quantum well (MQW) blue light-emitting diode fabricated on the low defect density (DD) freestanding GaN substrate were investigated. The electroluminescence (EL) peak at 2.74eV little shifted to the higher energy with the increase in current because of the absence of the polarization fields. The effective radiative lifetime increased and the nonradiative lifetime decreased with the increase in the junction field, and the results were quantitatively explained in terms of field-induced QCSE including tunneling escape of holes from the MQW. As a result of the use of the low DD substrate, the equivalent internal quantum efficiency, which was approximated as the spectrally integrated EL intensity at 300K divided by that at 150K, of 43% was achieved.

Quantum-confined Stark effects in the m-plane In0.15Ga0.85N∕GaN multiple quantum well blue light-emitting diode fabricated on low defect density freestanding GaN substrate

A light-emitting module includes a substrate, multiple light-emitting devices arranged thereon, and a package enclosing the multiple light-emitting devices. The package has multiple optical devices corresponding to the multiple light-emitting devices that converge and emit rays of light emitted from each of the light-emitting devices. When the outgoing rays of light emitted from the light-emitting device is extended toward the substrate, the package has virtual light-emitting regions spaced farther from the optical devices than the respective light-emitting devices, and the virtual light-emitting regions are located almost at the same position.

Jun Ichihara

Papers

Continuous-Wave Operation of m-Plane InGaN Multiple Quantum Well Laser Diodes

Dislocation-Free m-Plane InGaN/GaN Light-Emitting Diodes on m-Plane GaN Single Crystals

Method of manufacturing semiconductor laser

Quantum-confined Stark effects in the m-plane In0.15Ga0.85N∕GaN multiple quantum well blue light-emitting diode fabricated on low defect density freestanding GaN substrate

Light-emitting module and light-emitting unit