Impact of Hydrothermally Grown ZnO Nanorods on External Quantum Efficiency of 32 × 32 Pixelated InGaN/GaN Micro-LED Array

We systematically examined the growth parameters of the hydrothermally grown ZnO nanorods and studied their effects on the external quantum efficiency of 32 × 32 pixelated InGaN/GaN microlight-emitting diodes (μ-LEDs). The growth temperature increased the growth rate of the hydrothermally grown ZnO nanorods in the c-axis direction but not in the a-axis direction. On the other hand, the concentration of reaction solution increased the growth rate in the c-axis direction as well as the lateral growth rate of ZnO nanorods. The pressure of autoclave reactor had little influence on ZnO growth. The external quantum efficiency and light output power of the 32 × 32 pixelated InGaN/GaN μ-LEDs with the hydrothermally grown ZnO nanorods on the sapphire substrate were enhanced by 16.4% and 16.0% at 83 A/cm
²
, respectively, compared to those of the μ-LEDs without the ZnO nanorods, which can be attributed to increased light extraction due to the ZnO nanorods.