Strain relaxation and size variation of epitaxial Ge nanostructures on 4H-SiC (0001)

Abstract

The epitaxial growth of germanium (Ge) on wide-bandgap semiconductors, such as 4H-silicon carbide (4H-SiC), offers a promising platform for integrating group IV materials with high-power electronic substrates. In this work, the morphological and structural aspects of Ge nanostructures on SiC grown using molecular beam epitaxy (MBE) under ultra-high vacuum conditions are reported with an emphasis on particle size variation and strain relaxation. Determination of structural aspects and compositional analysis has been carried out using scanning electron microscopy (SEM) and Cross-sectional transmission electron microscopy (XTEM). Here, XTEM reveals a coherent and atomically sharp Ge/SiC interface, indicating the epitaxial nature of Ge growth. The observed growth follows a Stranski–Krastanov (SK) mode, where an initial wetting layer (~ 0.53 nm) precedes the formation of three-dimensional islands. Strain analysis using high-resolution TEM demonstrates a gradient in lattice relaxation within Ge nanostructures, with strain decreasing from ~ 20.0% at the Ge/SiC interface to ~ 1.5% at ~ 14 nm above the interface. Furthermore, Raman spectroscopy reveals a Ge–Ge vibrational Mode near 300 cm⁻¹, confirming the presence of high-quality Ge nanostructures. Here, we see that as the Ge layer thickness increases, the full width at half maximum (FWHM) of Ge Raman peaks decreases, indicating improvement in the crystalline quality. These findings provide fundamental insights into the epitaxial growth of Ge on SiC, which may improve device integration and is relevant to the advancement in the understanding of conventional low-bandgap materials on wide-bandgap materials.