Status and future outlook of III-V compound semiconductor visible-spectrum light-emitting diodes (LEDs) are presented. Light extraction techniques are reviewed and extraction efficiencies are quantified in the 60%+ (AlGaInP) and ~80% (InGaN) regimes for state-of-the-art devices. The phosphor-based white LED concept is reviewed and recent performance discussed, showing that high-power white LEDs now approach the 100-lm/W regime. Devices employing multiple phosphors for "warm" white color temperatures (~3000-4000 K) and high color rendering (CRI>80), which provide properties critical for many illumination applications, are discussed. Recent developments in chip design, packaging, and high current performance lead to very high luminance devices (~50 Mcd/m2 white at 1 A forward current in 1times1 mm2 chip) that are suitable for application to automotive forward lighting. A prognosis for future LED performance levels is considered given further improvements in internal quantum efficiency, which to date lag achievements in light extraction efficiency for InGaN LEDs

/pdf/status-and-future-of-high-power-light-emitting-diodes-for-3dktlyhlq0.pdf

Status and Future of High-Power Light-Emitting Diodes for Solid-State Lighting

We have developed methods for creating microscale inorganic light-emitting diodes (LEDs) and for assembling and interconnecting them into unusual display and lighting systems. The LEDs use specialized epitaxial semiconductor layers that allow delineation and release of large collections of ultrathin devices. Diverse shapes are possible, with dimensions from micrometers to millimeters, in either flat or “wavy” configurations. Printing-based assembly methods can deposit these devices on substrates of glass, plastic, or rubber, in arbitrary spatial layouts and over areas that can be much larger than those of the growth wafer. The thin geometries of these LEDs enable them to be interconnected by conventional planar processing techniques. Displays, lighting elements, and related systems formed in this manner can offer interesting mechanical and optical properties.

/pdf/printed-assemblies-of-inorganic-light-emitting-diodes-for-308viptb5o.pdf

Printed assemblies of inorganic light-emitting diodes for deformable and semitransparent displays.

Described herein are printable structures and methods for making, assembling and arranging electronic devices. A number of the methods described herein are useful for assembling electronic devices where one or more device components are embedded in a polymer which is patterned during the embedding process with trenches for electrical interconnects between device components. Some methods described herein are useful for assembling electronic devices by printing methods, such as by dry transfer contact printing methods. Also described herein are GaN light emitting diodes and methods for making and arranging GaN light emitting diodes, for example for display or lighting systems.

Printed assemblies of ultrathin, microscale inorganic light emitting diodes for deformable and semitransparent displays

Solid-state lighting is a rapidly evolving, emerging technology whose efficiency of conversion of electricity to visible white light is likely to approach 50% within the next several years. This efficiency is significantly higher than that of traditional lighting technologies, giving solid-state lighting the potential to enable significant reduction in the rate of world energy consumption. Further, there is no fundamental physical reason why efficiencies well beyond 50% could not be achieved, which could enable even more significant reduction in world energy usage. In this article, we discuss in some detail: (a) the several approaches to inorganic solid-state lighting that could conceivably achieve “ultra-high,” 70% or greater, efficiency, and (b) the significant research questions and challenges that would need to be addressed if one or more of these approaches were to be realized.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/lpor.200710019

Research challenges to ultra-efficient inorganic solid-state lighting

Solid-state lighting has made tremendous progress this past decade, with the potential to make much more progress over the coming decade. In this article, the current status of solid-state lighting relative to its ultimate potential to be “smart” and ultra-efficient is reviewed. Smart, ultra-efficient solid-state lighting would enable both very high “effective” efficiencies and potentially large increases in human performance. To achieve ultra-efficiency, phosphors must give way to multi-color semiconductor electroluminescence: some of the technological challenges associated with such electroluminescence at the semiconductor level are reviewed. To achieve smartness, additional characteristics such as control of light flux and spectra in time and space will be important: some of the technological challenges associated with achieving these characteristics at the lamp level are also reviewed. It is important to emphasise that smart and ultra-efficient are not either/or, and few compromises need to be made between them. The ultimate route to ultra-efficiency brings with it the potential for smartness, the ultimate route to smartness brings with it the potential for ultra-efficiency, and the long-term ultimate route to both might well be color-mixed RYGB lasers.

Toward Smart and Ultra-Efficient Solid-State Lighting

The temperature dependence of threshold current and quantum efficiency for Ga/sub x/In/sub 1-x/P (x=0.4, 0.6; lambda =680, 633 nm) single 80-AA quantum-well lasers is compared and analyzed using a model for the electron leakage current. This model fits the experimental data well, correctly describing the rapid increase in threshold and drop in quantum efficiency as temperature increases. Also, it indicates that the drift (rather than diffusion) component of the electron leakage current, is dominant, because of the poor p-type conductivity in AlGaInP. >

Drift leakage current in AlGaInP quantum-well lasers

The properties of (AlGa)/sub 0.5/In/sub 0.5/P, strained Ga/sub x/In/sub 1-x/P/(AlGa)/sub 0.5/In/sub 0.5/P heterostructures, and single quantum well (QW) laser diodes with Al/sub 0.5/In/sub 0.5/P cladding layers, prepared by low pressure organometallic vapor phase epitaxy, are described. The influence of biaxial strain upon the relative positions of the valence band edges are examined by analyzing the polarized spontaneous emission. Laser diodes with wavelength 620 >

Strained Ga/sub x/In/sub 1-x/P/(AlGa)/sub 0.5/In/sub 0.5/P heterostructures and quantum-well laser diodes

Low threshold GaxIn1−xP/(AlyGa1−y)0.5In0.5P strained quantum well lasers

We report output powers exceeding 45 mW, under CW, room temperature operation from single mode AlGaInP visible lasers emitting at 636 run. Threshold currents as low as 30 mA and single mode output powers of 40 mW have been obtained.

Low threshold, high power, single mode 630 nm lasers

The properties of (AlGa), ,In0 5P, strained Ga,Inl-,P/(AlGa)o 51110 5P heterostructures, and single quantum well (QW) laser diodes with A10 51110 SP cladding layers, prepared by low pressure organometallic vapor phase epitaxy, are described. The influence of biaxial strain upon the relative positions of the valence band edges are examined by analyzing the polarized spontaneous emission. Laser diodes with wavelength 620 < A < 690 nm are also fabricated, using active regions of biaxially strained GahP or AIGaInP. At longer wavelengths, threshold current densities under 200 A/cm2 and efficiencies greater than 80% result from a biaxially-compressed GaInP QW active region. Short wavelength AlGaInP laser performance is hindered by the poor electron confinement afforded by AlGaInP heterostructures. Despite the electron leakage problem, good 630-nm band performance, and extension into the 620-nm band, is achieved with strained, single QW active regions.

http://ieeexplore.ieee.org/iel5/3/7019/00283808.pdf

D.F. Welch

Papers

Drift leakage current in AlGaInP quantum-well lasers

Strained Ga/sub x/In/sub 1-x/P/(AlGa)/sub 0.5/In/sub 0.5/P heterostructures and quantum-well laser diodes

Low threshold GaxIn1−xP/(AlyGa1−y)0.5In0.5P strained quantum well lasers

Low threshold, high power, single mode 630 nm lasers

Strained GaJn 1 -zP/(AIGa)o, 5P Heterostructures and Quantum-Well Laser Diodes