Abstract
Status and future outlook of III-V compound semiconductor
visible-spectrum light-emitting diodes (LEDs) are presented. Light extraction
techniques are reviewed and extraction efficiencies are quantified in the
60%+ (AlGaInP) and ~80% (InGaN) regimes for state-of-the-art
devices. The phosphor-based white LED concept is reviewed and recent performance
discussed, showing that high-power white LEDs now approach the 100-lm/W regime.
Devices employing multiple phosphors for “warm” white color temperatures
(~3000–4000
K) and high color rendering (CRI > 80), which provide properties critical for many illumination applications,
are discussed. Recent developments in chip design, packaging, and high current
performance lead to very high luminance devices (~50 Mcd/m<sup>2</sup> white at 1 A forward current
in 1 x 1 mm<sup>2</sup> chip) that are suitable for application to automotive forward lighting.
A prognosis for future LED performance levels is considered given further
improvements in internal quantum efficiency, which to date lag achievements
in light extraction efficiency for InGaN LEDs.
© 2007 IEEE
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