Light-Emitting Diodes. (Monographs in Electrical and Electronic Engineering.) By A. A. Bergh and P. J. Dean. Pp. viii+591. (Clarendon: Oxford; Oxford University: London, 1976.) £22.

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Light-emitting diodes

Industries such as the automotive, aerospace or military, as well as environmental and biological research have promoted the development of ultraviolet (UV) photodetectors capable of operating at high temperatures and in hostile environments. UV-enhanced Si photodiodes are hence giving way to a new generation of UV detectors fabricated from wide-bandgap semiconductors, such as SiC, diamond, III-nitrides, ZnS, ZnO, or ZnSe. This paper provides a general review of latest progresses in wide-bandgap semiconductor photodetectors.

https://iopscience.iop.org/article/10.1088/0268-1242/18/4/201/pdf

Wide-bandgap semiconductor ultraviolet photodetectors

Wide-band-gap GaN and Ga-rich InGaN alloys, with energy gaps covering the blue and near-ultraviolet parts of the electromagnetic spectrum, are one group of the dominant materials for solid state lighting and lasing technologies and consequently, have been studied very well. Much less effort has been devoted to InN and In-rich InGaN alloys. A major breakthrough in 2002, stemming from much improved quality of InN films grown using molecular beam epitaxy, resulted in the bandgap of InN being revised from 1.9 eV to a much narrower value of 0.64 eV. This finding triggered a worldwide research thrust into the area of narrow-band-gap group-III nitrides. The low value of the InN bandgap provides a basis for a consistent description of the electronic structure of InGaN and InAlN alloys with all compositions. It extends the fundamental bandgap of the group III-nitride alloy system over a wider spectral region, ranging from the near infrared at ∼1.9 μm (0.64 eV for InN) to the ultraviolet at ∼0.36 μm (3.4 eV for GaN...

When group-III nitrides go infrared: New properties and perspectives

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 the time-reversed counterpart to laser emission, incident coherent optical fields are perfectly absorbed within a resonator that contains a loss medium instead of a gain medium. The incident fields and frequency must coincide with those of the corresponding laser with gain. We demonstrated this effect for two counterpropagating incident fields in a silicon cavity, showing that absorption can be enhanced by two orders of magnitude, the maximum predicted by theory for our experimental setup. In addition, we showed that absorption can be reduced substantially by varying the relative phase of the incident fields. The device, termed a “coherent perfect absorber,” functions as an absorptive interferometer, with potential practical applications in integrated optics.

https://science.sciencemag.org/content/sci/331/6019/889.full.pdf

Time-reversed lasing and interferometric control of absorption.

GaN-nanocolumn-based InGaN/GaN multiple quantum disk (MQD) light-emitting diodes (LEDs) with a novel columnar structure were fabricated on n-type (111) Si substrates. The n-GaN and InGaN/GaN MQD active region had isolated columnar structures, while the diameters were gradually increased in the p-GaN region by controlling the growth conditions. Consequently, the nanocolumn LED had a continuous surface without chasms. This novel structure enables p-type electrodes to be fabricated by the conventional method on top of nanocolumn devices while keeping the superior optical properties of the isolated nanocolumn active region. The nanocolumn LED showed clear rectifying behavior with a typical turn-on voltage of 2.5–3.0 V at room temperature. Electroluminescence was observed through semitransparent electrodes with various emission colors from green (530 nm) to red (645 nm).

https://iopscience.iop.org/article/10.1143/JJAP.43.L1524/pdf

InGaN/GaN Multiple Quantum Disk Nanocolumn Light-Emitting Diodes Grown on (111) Si Substrate

Columnar GaN nanostructures (GaN nanocolumns) were grown on Al2O3(0001) by RF-radical source molecular beam epitaxy (RF-MBE) through a self-organization process. The nanocolumns were grown at high density, with the c-axis maintained perpendicular to the substrate surface. The dependence of column diameter and density on growth conditions was systematically investigated. The average diameter was minimized to 53 nm and the density of the GaN nanocolumns was 130×1012 columns per square meter.

https://iopscience.iop.org/article/10.1143/JJAP.36.L459/pdf

Growth of Self-Organized GaN Nanostructures on Al2O3(0001) by RF-Radical Source Molecular Beam Epitaxy

A novel technology for controlling the In composition of InGaN quantum wells on the same wafer was developed, which paved the way for the monolithic integration of three-primary-color nano-light-emitting diodes. In the experiment, InGaN/GaN multiple quantum well nanocolumn arrays with nanocolumn diameters from 137 to 270 nm were prepared on the same substrate with the Ti-mask selective area growth by rf-plasma-assisted molecular beam epitaxy. The emission color changed from blue to red (from 479 to 632 nm in wavelength) with increasing nanocolumn diameter. The emission color change mechanism was clearly explained by the beam shadow effect of the neighboring nanocolumns.

Emission color control from blue to red with nanocolumn diameter of InGaN/GaN nanocolumn arrays grown on same substrate

Improved Ti-mask selective-area growth (SAG) by rf-plasma-assisted molecular beam epitaxy demonstrating extremely uniform GaN nanocolumn arrays

The Ti-mask selective-area growth (SAG) of GaN on Ti-nanohole-patterned GaN templates by rf-plasma-assisted molecular-beam epitaxy was employed to demonstrate the fabrication of regularly arranged InGaN/GaN nanocolumns. The SAG of GaN nanocolumns strongly depended on the growth temperature (Tg); at Tg below 900 °C, no SAG occurred, but above 900 °C, SAG occurred. However, an excessive increase in Tg to above 900 °C at a nitrogen flow rate (QN2) of 3.5 sccm brought about increased inhomogeneity in the nanocolumn shape. Upon reducing QN2 from 3.5 to 1 sccm, uniform nanocolumn arrays were successfully grown around the critical temperature of 900 °C.

https://iopscience.iop.org/article/10.1143/APEX.1.124002/pdf

Katsumi Kishino

Papers

InGaN/GaN Multiple Quantum Disk Nanocolumn Light-Emitting Diodes Grown on (111) Si Substrate

Growth of Self-Organized GaN Nanostructures on Al2O3(0001) by RF-Radical Source Molecular Beam Epitaxy

Emission color control from blue to red with nanocolumn diameter of InGaN/GaN nanocolumn arrays grown on same substrate

Improved Ti-mask selective-area growth (SAG) by rf-plasma-assisted molecular beam epitaxy demonstrating extremely uniform GaN nanocolumn arrays

Ti-mask Selective-Area Growth of GaN by RF-Plasma-Assisted Molecular-Beam Epitaxy for Fabricating Regularly Arranged InGaN/GaN Nanocolumns