M. George Craford

Chapter 2 Overview of Device Issues in High-Brightness Light-Emitting Diodes

Publisher Summary The key components of the luminous performance are the internal quantum efficiency and the extraction efficiency. The definition of the luminous performance efficiency and approaches used to optimize it are discussed in the chapter. Performance at this level would establish light-emitting diodes (LEDs) as the most efficient light source available and could conceivably lead to penetration of the commercial lighting industry in the decades ahead. These issues are discussed in the chapter. The progress in LED performance has been driven primarily by improvements in materials growth technology that have yielded higher purity and lower defect density materials with resulting higher quantum efficiencies. However, a variety of other issues such as cost, reliability, and extraction efficiency are also key drivers that determine commercial success and in some cases largely determine which growth technology is used. These issues are discussed in the chapter.

An overview of early studies on persistent photoconductivity and other properties of deep levels in GaAsP: the effect of deep levels on light emitting devices

Laser studies carried out at the University of Illinois in 1966 showed that the shortest wavelength at which lasing could be achieved in GaAsP was dependent on then-type dopant. In particular sulfur doping was found to restrict lasing to longer wavelengths. It was suggested that this could be due to the effect of energy levels associated with the higher conduction band minima. This led in 1967 to an investigation of the effect of Te and S donor levels on the properties of GaAsP near the direct-indirect crossover. Samples throughout the composition range were studied using Hall effect measurements from 55 to 400° K and resistivity measurements under hydrostatic pressure between 0 and 7 kbar at 300, 195, and 77° K. The data on Te-doped samples fit the standard energy band models, but S doping was found to exhibit dramatic persistent photoconductivity and other compositional effects similar to the “DX-center” effects later observed in AlGaAs and other materials. This paper summarizes these results on GaAsP:S, and gives a brief overview of other early investigations in compound semiconductors where energy levels associated with higher lying minima were studied and where, in some cases, nonequilibrium effects were observed. A later study on GaAsP:S is also described which shows the effect of S-doping on LED performance. Finally, some of the implications that the existence of deep levels of this type have on light emitting device performance in other alloy systems is discussed.

Light-Emitting Diode Displays

The intent of this chapter is to give an overview of issues in LED technology that are important to an engineer considering the use of LEDs for display applications. An attempt has been made to make this chapter self-contained. Due to space limitations, however, many topics are only briefly discussed. Additional information on various portions of LED technology is available in a number of books and review articles1–9 and the reader is referred to these publications if he wishes to pursue the topic further.

50th Anniversary of the Light-Emitting Diode (LED): An Ultimate Lamp [Scanning the Issue]

The articles in this special issue focus on the history and development of light emitting diode (LED) technology and industry applications over the last fifty years.

Diodes, Light-emitting

A light-emitting diode (LED) is a semiconductor device that emits monochromatic ultraviolet, visible, or infrared electromagnetic radiation when an electric current is passed through it. The semiconductor material is a compound or alloy of elements from columns III and V of the periodic table. Light-emitting diodes are compact, mechanically rugged, energy efficient, are of low voltage, and have long operating lifetimes. For colored lighting applications, the efficiency of LEDs far exceeds that of filtered incandescent sources and they are becoming the dominant technology. LEDs are widely used as indicator lights, for backlighting small displays in electronic equipment, in exterior and interior lighting of automobiles, in large-area full-color displays, and for data communication. LEDs will be used for general white-light illumination purposes to the extent that the energy efficiency improves and higher-power, higher-flux devices become available. Keywords: light-emitting diode; compound semiconductor; solid-state lighting; energy gap; visible; LPE; MOVPE