LED Light Extraction via AlGaN-GaN Differential Etching

The patent applies local quality by creating a mixed-material surface structure where AlGaN and GaN regions coexist. The AlGaN material etches at a different rate than GaN, producing locally distinct feature types (peaks and valleys) with varying sharpness. This local material differentiation enables sharper, more distinct surface topology that enhances light extraction efficiency compared to uniform material roughening.

The patent employs composite materials by combining AlGaN and GaN layers in the light-emitting structure. This composite approach allows differential etching rates during the roughening process, creating a heterogeneous surface morphology with sharper features. The composite material strategy directly addresses the limitation of conventional single-material roughening by producing more effective light-scattering topography.

The patent applies preliminary action by incorporating the AlGaN epitaxial layer during the initial device fabrication process, before the roughening step. This pre-positioning of the differential-material layer ensures that subsequent roughening automatically produces the desired sharp feature topology without requiring additional post-processing steps. The complexity is built-in during standard epitaxial growth rather than added later.

The patent utilizes parameter changes by varying the material composition (Al content in AlGaN) to control etching behavior. By adjusting the epitaxial growth parameters to create a thin AlGaN layer with specific thickness and composition, the differential etching rate is optimized to produce sharp features. This parameter-based control achieves the desired morphology through material science rather than complex mechanical or chemical processing.