High-power light-emitting diodes (LEDs) have begun to differentiate themselves from their more common cousins the indicator LED. Today these LEDs are designed to generate 10-100 lm per LED with efficiencies that surpass incandescent and halogen bulbs. After a summary of the motivation for the development of the high-power LED and a look at the future markets, we describe the current state of high-power LED technology and the challenges that lay ahead for development of a true "solid state lamp." We demonstrate record performance and reliability for high-power colored and white LEDs and show results from the worlds first 100-plus lumen white LED lamp, the solid state equivalent of Thomas Edison's 20-W incandescent lightbulb approximately one century later.

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 (approximate to1-5 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 (approximate to50 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-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 350mW (1A dc, 300K) with low (< 4V) forward voltages. The performance of these LEDs is demonstrated in terms of output power, efficiency, and electrical characteristics.

Data are presented on high-power AlGaInN flip-chip light-emitting diodes (FCLEDs). The FCLED is “flipped-over” or inverted compared to conventional AlGaInN light-emitting diodes (LEDs), and light is extracted through the transparent sapphire substrate. This avoids light absorption from the semitransparent metal contact in conventional epitaxial-up designs. The power FCLED has a large emitting area (∼0.70 mm2) and an optimized contacting scheme allowing high current (200–1000 mA, J∼30–143 A/cm2) operation with low forward voltages (∼2.8 V at 200 mA), and therefore higher power conversion (“wall-plug”) efficiencies. The improved extraction efficiency of the FCLED provides 1.6 times more light compared to top-emitting power LEDs and ten times more light than conventional small-area (∼0.07 mm2) LEDs. FCLEDs in the blue wavelength regime (∼435 nm peak) exhibit ∼21% external quantum efficiency and ∼20% wall-plug efficiency at 200 mA and with record light output powers of 400 mW at 1.0 A.

The performance of high-power AlInGaN light emitting diodes (LEDs) is characterized by light output-current-voltage (L-I-V) measurements for devices with peak emission wavelengths ranging from 428 to 545 nm. The highest external quantum efficiency (EQE) is measured for short wavelength LEDs (428 nm) at approximate to 29%. EQE decreases with increasing wavelength, reaching approximate to 13% at 527 nm. With low forward voltages ranging from approximate to3.3 to approximate to2.9 V at a drive current density of 50 A/cm(2), these LEDs exhibit power conversion efficiencies ranging from approximate to 26% (428 nm) to approximate to 10% (527 nm).

Variable-temperature Hall-effect measurements were employed to optimize doping for GaN layers utilized in blue, blue-green and green light emitting diodes (LEDs). N-type doping was accomplished by doping with Si, Ge, and O, and the electronic properties of these donors were studied. Si and Ge, which substitute for Ga, are shallow donors with almost identical activation energies for ionization (ca. 17 and ca. 19 meV, respectively, for a donor concentration of ca. 3×1017 cm−3). O substitutes for N and introduces a slightly deeper donor level into the bandgap of GaN having an activation energy of ca. 29 meV (for a donor concentration of ca. 1×1018 cm−3). Mg doping was employed to achieve p-type conductivity for GaN device layers. Mg substitutes for Ga introducing a relatively deep acceptor level. For the analysis of the variable-temperature Hall-effect data, it was found important to take the coulomb interaction between ionized acceptors into account, leading to lower activation energy with increasing degree of ionization (increasing temperature). The activation energy for ionization of Mg acceptors in GaN was thus estimated to be (208±6) meV for very low acceptor concentrations. Using optimized nitride layers, LEDs with typical external quantum efficiencies of ca. 10% in the blue and blue-green, and ca. 8% in the green wavelength range were achieved. Due to optimized doping, the forward voltages for these diodes were as low as 3.2 V at 20 mA drive current.

High-efficiency InGaN single and multiple quantum well (SQW and MQW) light emitting diodes (LEDs) emitting in the blue, cyan and green spectral ranges have been produced on sapphire substrates by low-pressure, organometallic vapor phase epitaxy (OMVPE). Initiation of growth on these mismatched substrates was achieved by using a novel InGaN/GaN nucleation layer. At 20 mA typical commercial devices have approximately 8-10% external quantum efficiency in cyan (similar to 500 nm) and 6-9% in green (similar to 520 nm). These diodes exhibited forward voltages of 3.1-3.3 V at 20 mA.

A new class of LEDs based on the AlGaInP material system first became commercially available in the early 1990's. These devices benefit from a direct bandgap from the red to the yellow-green portion of the spectrum. The high efficiencies possible in AlGaInP across this spectrum have enabled new applications for LEDs including automotive lighting, outdoor variable message signs, outdoor large screen video displays, and traffic signal lights. A review of high-brightness AlGaInP LED technology will be presented.

Semiconductor wafer bonding is employed to fabricate very high efficiency transparent-substrate (TS) AlGaInP light-emitting diodes (LEDs) with projected lifetimes in excess of 100 000 h under accelerated life test at an ambient temperature of 55 degrees C (70 A/cm(2)). Furthermore, we demonstrate wafer-bonded TS AlGaInP red LEDs with external quantum efficiencies of 23.7% at 635.6 nm (20 mA, DC, 250 degrees C).

The electrical, optical, and structural properties of light emitting diodes (LEDs) fabricated from the III–V nitride material system have been studied. LEDs with external quantum efficiencies as high as 4% were characterized by transmission electron microscopy and found to contain dislocation densities in excess of 2×1010 cm−2. A comparison to other III–V arsenide and phosphide LEDs shows that minority carries in GaN-based LEDs are remarkably insensitive to the presence of structural defects. Dislocations do not act as efficient nonradiative recombination sites in nitride materials. It is hypothesized that the benign character of dislocations arises from the ionic nature of bonding in the III–V nitrides.

Data are presented demonstrating the operation of transparent-substrate (TS) (AlxGa1−x)0.5In0.5P/GaP light-emitting diodes (LEDs) whose efficiency exceeds that afforded by all other current LED technologies in the green to red (560–630 nm) spectral regime. A maximum luminous efficiency of 41.5 lm/W (93.2 lm/A) is realized at λ∼604 nm (20 mA, direct current). The TS (AlxGa1−x)0.5In0.5P/GaP LEDs are fabricated by selectively removing the absorbing n-type GaAs substrate of a p-n (AlxGa1−x)0.5In0.5P double heterostructure LED and wafer bonding a ‘‘transparent’’ n-GaP substrate in its place. The resulting TS (AlxGa1−x)0.5In0.5P/GaP LED lamps exhibit a twofold improvement in light output compared to absorbing-substrate (AS) (AlxGa1−x)0.5In0.5P/GaAs lamps.