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 (SiO2) film as a passivation layer. The SiO2 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 SiO2 films. AFM measurements demonstrate that the SiO2 surface roughness was larger at a lower deposition temperature than a higher temperature. Forward voltage (Vf) characteristics of these PEC LEDs were detected and recorded for continuous ten thousand probe times. The curve of Vf remained stable at temperatures of 150, 200 and 250 °C. A metal-insulator-metal structure using 250 °C-deposited SiO2 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 SiO2 (20 nm) was 3.65. The ultra-thin SiO2 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 SiO2 film as a passivation layer.