Improving performances of ultra-small size (1-20 m) InGaN red micro-LEDs by growing on freestanding GaN substrates

The ultra-small size InGaN red micro-LED has attracted a lot of research interest for AR micro-display applications. However, it still faces the challenge of maintaining the emission wavelength and efficiency that meet the needs of micro-display in small size and high current density. Here, we demonstrate 1-20 mu m InGaN red micro-LEDs based on freestanding GaN substrates, showing enhanced indium incorporation compared with those grown on traditional sapphire substrates. For the 1 mu m devices, an external quantum efficiency (on-wafer) of 0.86% and a wavelength of 613.6 nm are achieved at a current density of 50 A/cm(2). In addition, the emission uniformity of 1 mu m array grown on GaN substrates is significantly superior to that grown on sapphire substrates. These results indicate that freestanding GaN substrates are benefits for improving performance of red InGaN micro-LEDs.