The high power GaN-based blue light emitting
diode (LED) on an 80-μm-thick GaN template is proposed and even realized by
several technical methods like metal organic chemical vapor deposition (MOCVD),
hydride vapor-phase epitaxial (HVPE), and laser lift-off (LLO). Its advantages
are demonstrated from material quality and chip processing. It is investigated
by high resolution X-ray diffraction (XRD), high resolution transmission
electron microscope (HRTEM), Rutherford back-scattering (RBS),
photoluminescence, current-voltage and light output-current measurements. The
width of (0002) reflection in XRD rocking curve, which reaches 173'' for the
thick GaN template LED, is less than that for the conventional one, which
reaches 258''. The HRTEM images show that the multiple quantum wells (MQWs) in
80-μm-thick GaN template LED have a generally higher crystal quality. The light
output at 350 mA from the thick GaN template LED is doubled compared to
traditional LEDs and the forward bias is also substantially reduced. The high
performance of 80-μm-thick GaN template LED depends on the high crystal
quality. However, although the intensity of MQWs emission in PL spectra is
doubled, both the wavelength and the width of the emission from thick GaN
template LED are increased. This is due to the strain relaxation on the surface
of 80-μm-thick GaN template, which changes the strain in InGaN QWs and leads to
InGaN phase separation.
Source:IOPscience
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