Mechanical decoupling epitaxy via compliant microdisks yields relaxed transferable AlGaN across broad compositions

Achieving high-quality, crack-free AlGaN layers across a wide aluminum composition range is critical for ultraviolet optoelectronics but remains challenging due to strain-induced defects from lattice and thermal mismatches. Here we present a mechanical decoupling epitaxy approach wherein compliant Al0.15Ga0.85N microdisks supported by GaN pillars accommodate strain during subsequent regrowth, enabling fully relaxed, crack-free AlxGa1-xN up to 82% Al and threading dislocation densities comparable to the initial GaN template (~2-5 × 10⁸ cm⁻²). Plastic relaxation via misfit dislocations is confined to the supporting GaN pillars, allowing elastic deformation of the microdisk and preserving the structural quality of the overlayer. The resulting AlGaN micropallets support UVB emission from multiple quantum wells and can be mechanically transferred onto arbitrary substrates without degradation. This strategy decouples strain relaxation from substrate constraints, offering a versatile pathway toward high-quality AlGaN templates and advancing efficient UV micro-optoelectronic device development.