Strain-released epitaxy of GaN enabled by compliant single-crystalline metal foils

TL;DR

This paper demonstrates a novel strain-released epitaxy method for GaN on compliant single-crystalline copper foils, reducing defects and enabling efficient micro-LED arrays.

Contribution

It introduces a substrate-mediated strain-partitioning regime using compliant single-crystalline metal foils, a new approach in heteroepitaxial growth.

Findings

GaN grown on copper foils is nearly strain-free despite large mismatch.

Elastic deformation of copper screens mismatch-induced stress.

Dense GaN micro-LED arrays with improved electrical and thermal performance.

Abstract

Heteroepitaxy conventionally relies on rigid crystalline substrates, implicitly assuming that lattice and thermal mismatch must be accommodated within the epitaxial layer, leading to residual strain and defects that worsen with increasing substrate size. Here we demonstrate a substrate-mediated strain-partitioning regime in which lattice and thermal mismatch are preferentially partitioned into the substrate rather than stored in the epitaxial layer. We report the epitaxial growth of single-crystalline GaN on mechanically compliant yet crystallographically ordered single-crystalline copper foils. Atomic-resolution microscopy, geometric phase analysis and density functional theory reveal that mismatch-induced stress is primarily screened by elastic deformation of the Cu lattice, accompanied by localized interfacial slip confined to a few atomic layers, leaving the AlN and GaN epilayers nearly strain-free despite large nominal mismatch. Leveraging this strain-released epitaxial platform, we further demonstrate dense GaN micro-light-emitting diode arrays that benefit from efficient vertical electrical conduction and thermal dissipation enabled by the metallic substrate. By establishing compliant single-crystal metal foils as a new substrate class, this work identifies mechanical contrast as an underexplored governing parameter in heteroepitaxial design, with implications extending beyond GaN.