Backside reflector using metallic mirror and ALD-TiO2/Al2O3 DBR for GaN-based LED

In this work, high reflectivity backside reflectors combining TiO₂/Al₂O₃ distributed Bragg reflector (DBR) by atomic layer deposition (ALD) with metallic mirror have been demonstrated for the first time. Multi-pair-DBRs/Al and multi-pair-DBRs/Ag stacks with excellent uniformity and thickness accuracy have exhibited high reflectance above 96%. Optimized thicknesses of Al₂O₃ (67 nm) and TiO₂ (49 nm) were figured out to achieve the highest reflectance. The reflectance of the fabricated backside reflectors were verified by both simulation and spectroscopic ellipsometry measurement, and the measured data coincide with the simulated data well. Since TiO₂/Al₂O₃ DBR has good adhesion with both sapphire substrate and Al mirror, we simplified the fabrication process and achieved more stabilized backside reflector. By combining ALD deposition with TiO₂/Al₂O₃ DBR, high reflectivity, less angle dependency, more stabilized and excellent film uniformity backside reflector is achieved to meet the requirements of high brightness light-emitting diodes (LEDs).