Cost-effective solid state lighting based on GaN-on-Si technology

Epitaxial integration of GaN on silicon is widely deemed as one of the most effective approaches for a significant cost reduction of solid state lighting, but was hindered by the crack problem due to the huge mismatch in the coefficient of thermal expansion (CTE) between GaN and Si. The stress compensation scheme with an AlN/AlGaN multilayer buffer has been experimentally verified with a great reproducibility in achieving high-quality crack-free GaN film on Si substrates, upon which InGaN/GaN multiple quantum wells and p-type layers are overgrown. The as-grown LED/Si wafers are processed into thin film vertical structure LEDs with the epitaxial Si substrate removed. We have commercialized GaN-on-Si LEDs with an average efficacy of 120-130 lm/W for 1mm² LED chips at 350 mA, which have passed the 6000-hour LM80 reliability test. The GaN-on-Si LEDs featured with single-side emission and a Lambertian distribution can apply wafer-level phosphor coating process and are suitable for directional lighting, streetlight and flash applications. Four 55 mil × 55 mil chips co-packaged in a 7070 ceramic package have been used to build an MR16 spot light.