Dynamic Wafer Curvature Engineering Toward Ultraflat and Highly Uniform 8‐Inch GaN Heteroepitaxy

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Large‐area GaN heteroepitaxy is essential for next‐generation electronic and optoelectronic systems, yet simultaneously achieving low wafer bow and high epitaxial uniformity remains challenging due to the dynamic evolution of thermo‐mechanical stress during growth and cooling. Here, we develop a dynamic wafer curvature engineering strategy based on a thermal‐cycling stress‐loading (TCSL) layer to regulate curvature evolution throughout epitaxy and suppress residual bow after cooling. The TCSL layer consists of a hydrogen‐rich SiO 2 film deposited on the backside of sapphire substrates, where hydrogen‐driven viscoelastic relaxation and dehydrogenation‐induced network densification generate asymmetric stress evolution. Applying this strategy to AlGaN/GaN HEMT epitaxy, we realize ultraflat and highly uniform 8‐inch wafers on 1‐mm‐thick sapphire substrates, achieving a bow of 7.4 µm, a warp of 17.2 µm, and relative standard deviations of 0.82%, 1.2%, and 1.8% for epitaxial thickness, Al composition, and sheet resistance, respectively. The AlGaN/GaN heterostructure preserves high crystalline and interfacial quality, enabling a high‐quality two‐dimensional electron gas with a sheet density of 7.0 × 10 12 cm −2 and an electron mobility of 2040 cm 2 /V·s. This work establishes a scalable approach for simultaneous control of wafer flatness and epitaxial uniformity in large‐area GaN heteroepitaxy, paving the way toward highly integrated GaN‐based electronic and optoelectronic technologies.