High Performance GaN-Based LEDs on Patterned Sapphire Substrate with Patterned Composite SiO2/Al2O3 Passivation Layers And TiO2/Al2O3 DBR Backside Reflector

GaN-based light-emitting diodes (LEDs) on patterned sapphire substrate (PSS) with patterned composite SiO2/Al2O3 passivation layers and TiO2/Al2O3 distributed Bragg reflector (DBR) backside reflector have been proposed and fabricated. Highly passivated Al2O3 layer deposited on indium tin oxide (ITO) layer with excellent uniformity and quality has been achieved with atomic layer deposition (ALD) technology. With a 60 mA current injection, an enhancement of 21.6%, 59.7%, and 63.4% in the light output power (LOP) at 460 nm wavelength was realized for the LED with the patterned composite SiO2/Al2O3 passivation layers, the LED with the patterned composite SiO2/Al2O3 passivation layers and Ag mirror + 3-pair TiO2/SiO2 DBR backside reflector, and the LED with the patterned composite SiO2/Al2O3 passivation layer and Ag mirror + 3-pair ALD-grown TiO2/Al2O3 DBR backside reflector as compared with the conventional LED only with a single SiO2 passivation layer, respectively.

Periodic triangle truncated pyramid arrays are successfully fabricated on the sapphire substrate by a low-cost and high-efficiency laser interference lithography (LIL) system. Through the combination of dry etching and wet etching techniques, the nano-scale patterned sapphire substrate (NPSS) with uniform size is prepared. The period of the patterns is 460 nm as designed to match the wavelength of blue light emitting diode (LED). By improving the stability of the LIL system and optimizing the process parameters, well-defined triangle truncated pyramid arrays can be achieved on the sapphire substrate with diameter of 50.8 mm. The deviation of the bottom width of the triangle truncated pyramid arrays is 6.8%, which is close to the industrial production level of 3%.


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