Characterization of large-area AlGaInP/mirror/Si light-emitting diodes fabricated by wafer bonding

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 150mA injection and for the large-area LED (1200 × 1200 μm²) to increase output power even at 300mA 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.