Metal-Modulated Growth of Cubic, Red-Emitting InGaN Layers and Self-Assembled InGaN/GaN Quantum Wells by Molecular Beam Epitaxy

Cubic InGaN alloys are a promising candidate material for next-generation optoelectronic applications as they lack internal fields and promise to cover large parts of the electromagnetic spectrum from the deep UV toward the mid-infrared. This demands high-quality epitaxial growth of cubic InGaN/GaN quantum wells, especially for the red energy range. However, the growth of indium-bearing nitride quantum wells in the metastable cubic phase still poses many challenges. InGaN and GaN are typically grown at different temperatures and with different metal fluxes in molecular beam epitaxy, leading to either long waiting periods for temperature adjustment or growth under suboptimal conditions. Both degrade the crystal quality and optical properties. In this study, we apply a metal-modulated growth approach in molecular beam epitaxy that enables us to grow either self-assembled, phase pure, cubic InGaN/GaN multi quantum wells (MQWs) or homogeneous c-InGaN layers, only by adjusting the shutter duration times for Ga and In. We achieve smooth surfaces and sharp interfaces with a quantum well thickness tunable from 6 to 16 nm and a barrier thickness ranging from 4 to 10 nm. X-ray diffraction confirms >99% phase purity of our cubic layers, while time-of-flight secondary ion mass spectrometry, scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy provide detailed information on the quantum well composition and strain. Photoluminescence measurements at room temperature demonstrate the emission properties of the samples, with the emission wavelength ranging from 540 to 670 nm. Changing the barrier and QW thickness results in a shift of emission energy of up to 400 meV, which is explained by quantum confinement and strain. The high interface quality and excellent optical properties of the quantum wells without the need for multiple metal sources or long waiting times represent a significant advance in the development of next-generation optoelectronic devices.