Vertical LEDs on Rigid and Flexible Substrates Using GaN-on-Si Epilayers and Au-Free Bonding

Vertical-injection light-emitting diodes (VLEDs) were fabricated and demonstrated on mechanically rigid and flexible substrates using GaN-on-Si epilayers and a cost-effective Au-free Cu/Sn bonding method. With a mirror layer between the VLEDs and the receptor Si(100) carrier, 500 μm × 500 μm VLEDs emit up to 134-mW optical power at a drive current of 300 mA. The peak wall-plug efficiency was 23% at 1-A/cm
²
current injection density. Due to excellent heat dissipation of the metal and Si carrier, the VLED junction temperature was measured to be only 47.5°C at a working current density of 350 mA/mm
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and increased by 0.27°C per 1-mA current increment. After release from the rigid substrate, the 40-μm-thick Cu/Sn/Cu bonding layer can also work as a handling substrate to paste LED thin films onto flexible substrates, including plastic and paper. The self-contained VLED structure exhibited the original I-V characteristics and high brightness on various substrates. The results attest to the feasibility of using GaN-on-Si epilayers and Cu/Sn/Cu bonding for a wide range of applications, including low-cost solid-state lighting and flexible illuminations.