Ultra-flat AlN grown with a pulsed H ₂ etching condition

A 1.5 μm AlN epilayer with a root-mean-square surface roughness of 0.25 nm was grown by metal-organic chemical vapor deposition at the single substrate temperature below 1200 °C. The ultra-flat surface is achieved with 30 min annealing performed in the initial growth, during which abrupt AlN hillocks are removed by pulsed H ₂ etching controlled via the on/off duration of NH ₃ supply. The pulsed etching technique effectively tailors the island-like morphology of the AlN buffer, facilitating the lateral crystal nucleation in subsequent growth. This study provides a simple, feasible and cost-effective manufacturing method for high-quality AlN.