Thermal Performance of III-Nitride Light Emitting Diodes and Developments in Laser Based White Lighting.

摘要

Light emitting diodes, LEDs, have two distinct reductions in their efficiency. Efficiency droop which is a decrease in efficiency with increasing current density, and thermal droop, a reduction in efficiency with increasing temperature. Although there has been extensive work on efficiency droop and research into both the mitigation and causes of efficiency droop, comparably little research has been done on thermal droop.;Since the early years of III-Nitride LEDs, have shown better performance than other materials systems used in visible light emitters when operated at increased temperatures. Due to the push for increased electrical efficiency thermal droop has been largely ignored or dealt with at a packaging level. Now LEDs are increasingly used in general illumination applications requiring high-current and high-flux operation resulting in elevated operating temperatures. In such high power applications LEDs can reach temperatures of over 100 °C where the performance can be significantly degraded. By altering the internal structure both below and within the active region the thermal droop of LEDs was reduced while preserving or enhancing electrical efficiency. Increased high temperature performance was observed on both blue c-plane and m-plane LEDs.;Electrical droop which adversely affects LEDs in general illumination applications is difficult to mitigate. As an alternative to high-current, high-luminous flux LEDs for general illumination, phosphor converted laser, pc-LD, based white lighting is demonstrated. pc-LD shows virtually droop free performance over a wide range of high current densities with high luminous flux levels. The ability to achieve efficiencies on par with pc-LEDs, with significantly reduced substrate use and extremely high current operation, suggests that pc-LD white lighting has potential for entry into select white lighting applications in the near future. First demonstrations of pc-LD white lighting with general illumination level fluxes are shown, achieving efficacies of 80 lm/W and luminous fluxes of greater than 1 kLm.