Jerome Chandra Bhat

High Power LEDs – Technology Status and Market Applications

High power light emitting diodes (LEDs) continue to increase in output flux with the best III-nitride based devices today emitting over 150 lm of white, cyan, or green light. The key design features of such products will be covered with special emphasis on power packaging, flip-chip device design, and phosphor coating technology. The high-flux performance of these devices is enabling many new applications for LEDs. Two of the most interesting of these applications are LCD display backlighting and vehicle forward lighting. The advantages of LEDs over competing lighting technologies will be covered in detail.

High‐Power III‐Nitride Emitters for Solid‐State Lighting

High-power, large-area InGaN/GaN quantum-well heterostructure light-emitting diodes based on an inverted, or flip-chip, configuration are described. These devices are mounted in specially designed high-power (1-5 W) packages and exhibit high extraction efficiency and low operating voltage. In the blue wavelength regime, output powers greater than 250 mW (1 x 1 mm 2 device) and 1 W (2 x 2 mm 2 device) are delivered at standard operating current densities (50 A/cm 2 ), corresponding to wall-plug efficiencies of 22%-23%. Employing phosphors for the generation of white light, these same devices achieve luminous efficiencies greater than 30 lm/W.

High-flux and high-efficiency nitride-based light-emitting devices

There are numerous materials challenges involved in the production of high-efficiency III-nitride lasers and LEDs, some of which can be mitigated by epitaxy and device physics. The lack of a suitable lattice-matched substrate for epitaxy of AlInGaN films results in high dislocation densities and a large amount of residual strain in the deposited films. The role of the dislocations is not well-understood, although there is clear evidence that laser reliability is improved by reducing their density.

High-power AlInGaN light-emitting diodes

High-power light-emitting diodes (LEDs) in both the AlInGaP (red to amber) and the AlGaInN (blue-green) material systems are now commercially available. These high-power LEDs enable applications wherein high flux is necessary, opening up new markets that previously required a large number of conventional LEDs. Data are presented on high-power AlGaInN LEDs utilizing flip-chip device structures. The high-power flip-chip LED is contained in a package that provides high current and temperature operation, high reliability, and optimized radiation patterns. These LEDs produce record powers of 350 mW (1A dc, 300 K) with low (<4V) forward voltages. The performance of these LEDs is demonstrated in terms of output power, efficiency, and electrical characteristics.