Reliability improvement of pad-extended on chip light-emitting diodes using an ultra-thin passivation layer

The pad-extended on chip (PEC) light-emitting diodes (LEDs) were fabricated and characterized by using an ultra-thin silicon oxide (SiO 2 ) film as a passivation layer. The SiO 2 thin film was deposited on the GaN mesa edge using plasma-enhanced chemical vapor deposition (PECVD) by varying deposition temperature from 150 to 350 °C. Atomic force microscopy (AFM), a scanning electron microscope (SEM) and leakage current were employed to analyze the influence of deposition temperature on the structural properties of SiO 2 films. AFM measurements demonstrate that the SiO 2 surface roughness was larger at a lower deposition temperature than a higher temperature. Forward voltage ( V f ) characteristics of these PEC LEDs were detected and recorded for continuous ten thousand probe times. The curve of V f remained stable at temperatures of 150, 200 and 250 °C. A metal-insulator-metal structure using 250 °C-deposited SiO 2 as the dielectric indicates the leakage current density was close to 10 −8 A cm −2 with the minimum one lower than 10 −12 A cm −2 . The relative dielectric constant of the SiO 2 (20 nm) was 3.65. The ultra-thin SiO 2 film efficiently passivated the GaN mesa edge and prevented charge accumulation at the surface. Reliability has been improved for PEC LEDs using the ultra-thin SiO 2 film as a passivation layer.