n-doped GaN layer (with a surplus of electrons) and a
p-doped GaN layer (with a surplus of holes). When a
forward voltage is applied between p-GaN and n-GaN,
the holes and electrons are driven into the active layer
where they meet (recombine) and transform into photons
(light). Prof Nakamura was instrumental in tuning these
technological breakthroughs into viable products for
various applications.
As material and fabrication technology matured in the last
two decades, high-brightness blue LEDs started to
revolutionize the illumination technology as a competitive
light source. In 2014, the highest LED luminous efficacy
has hit 303 lumens per watt (lm/W) in the laboratory, which
is more than 18 times of conventional incandescent bulbs
(16 lm/W) and 4 times of fluorescents (70 lm/W). With the
features of low power consumption, long lifetime (up to
100,000 hours), minimum maintenance, and non-toxicity
(no mercury contained), LEDs are used in a large number
of applications including traffic signals, display backlights,
automobile headlights, street lightings, and general indoor
lightings.
Established and led by Prof Kei May Lau, IAS Senior Fellow
in the Department of Electronic & Computer Engineering
at HKUST, the Photonics Technology Center (PTC) has
been carrying out research in GaN-based LEDs since 2001.
Researchers in PTC have invented a high-resolution LED
display technology, without any liquid crystal or organic
materials. The first 0.19 inch 1,700 pixels per inch (PPI)
passive-matrix GaN-based light-emitting diodes on silicon
(LEDoS) micro-display and the highest resolution (400 ×
240) active-matrix LEDoS micro-display were
demonstrated in 2014. LEDoS micro-display is more
advantageous in terms of brightness, power efficiency,
lifetime, thermal stability, and robustness in extreme
conditions. The main applications of LEDoS include
head-up display, head-mounted display and projector.
High power and high resolution (400 × 240) active-matrix
LEDoS micro-display as an alternative solution for projectors.
Feb 2015
Knowledge Corner
7
