High-brightness AlGaInP/mirror/barrier/Si
light-emitting diodes (LEDs) with vertical electrodes were fabricated using a
wafer bonding technique. The high-thermal-conductivity Si substrate provides a
better heat sink (compared with GaP or GaAs), which is a particularly important
characteristic for high-power, large-area emitter applications. It allows for
saturation of the small-area LED (300×300 µm2) after 150 mA injection and for
the large-area LED (1200×1200 µm2) to increase output power even at 300 mA
injection. The light output of the large-area vertical-conducting LED is mainly
affected by the top-side (i.e., n-AlGaInP cladding) electrode design, where an
interdigitated-finger electrode provides the better current spreading
performance and prevents the current crowding problem. The extent of junction
heating on LED samples (300×300–1200×1200 µm2) can also be evaluated from the
corresponding electroluminescence spectra and emission-peak-wavelength driven
by different injection current values. Finally, using a natural lithography
technique, the mirror-substrate (MS) LEDs with textured surfaces present a
brightness of 10 cd, which is about 4 cd brighter than that of the MS LED
without a textured surface. With a combination of the MS wafer bonding and
surface texturing techniques, thermal management in packaging becomes the key
factor in further enhancing the external quantum efficiency of large-area LEDs
under high flux operation.
Source:IOPscience
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