Troy A. Trottier

High-power phosphor-converted light-emitting diodes based on III-Nitrides

Phosphor conversion of light-emitting diode light for white light sources and some monochrome applications requires particular phosphor properties and has to take into account specific issues if aimed at high-power output. Limitations and solutions will be discussed, giving special considerations to drive and temperature dependencies. Efficiencies of 32 lm/W for white with good color rendering at 4600 K and 35 lm/W for green (535 nm) have been demonstrated.

Green phosphor-converted LED

Green phosphor-converted LEDs using a blue pump InGaN diodes have advantages over the direct green InGaN LED with regards to color stability with drive and/or temperature. Added manufacturing steps are outweighed by higher color yield, as a range of pump colors can be used without changing the final chromaticity. The conversion losses can be smaller than the decrease in wall-plug efficiency from blue towards green, which has been reported by many sources. A distinct disadvantage of the concept is due to only one color and phosphor proven - SrGa2S4:Eu2+ and 535 nm peak wavelength.

Photoluminescence and cathodoluminescence properties of green emitting SrGa2{S}4 : Eu2+ thin film

Photoluminescence and cathodoluminescence properties of SrGa2S4 : Eu2+ thin films prepared by reactive RF magnetron sputtering are investigated. Luminescence performances of the phosphor in the thin film form are compared to those of powder samples: the brightness efficiency of thin films is found to be about 30% of the efficiency of powder at low current density. A ratio higher than 40% is expected at higher current density. Thin film screens for FEDs will become a positive alternative to powder screens provided that film quality and light extraction could be improved by optimization of thickness and deposition parameters.

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.