Mechanism of Self-Assembled Cubic InGaN/GaN Quantum Well Formation in Metal-Modulated Molecular Beam Epitaxy

Alternating metal-modulated molecular beam epitaxy enables the growth of both self-assembled c-InGaN/GaN quantum wells and fully alloyed c-InGaN layers. <i>In situ</i> reflection high-energy electron diffraction (RHEED) analysis coupled with <i>ex situ</i> structural characterization investigates the growth mechanism and prerequisites for the self-assembled c-InGaN quantum well formation. The data reveal that indium accumulates without incorporating into the underlying c-GaN layer during an indium deposition step. However, the accumulated indium forms c-InGaN during a subsequent GaN growth step consistent with vertical cation segregation. Furthermore, X-ray diffraction, time-of-flight secondary ion mass spectrometry depth profiles, and scanning transmission electron microscopy imaging show homogeneous and well-defined c-InGaN layers. The presented growth mechanism requires high substrate temperatures and gallium fluxes. Still, limit testing suggests that indium contents of up to 37% are feasible. This encourages the implementation of metal-modulated grown c-InGaN in red light-emitting devices. Furthermore, combining RHEED operando diagnostics and a precise understanding of the growth mechanism is vital for progressing toward automated growth of complex heterostructures.