Hybrid Epitaxial Al/InGaAs system: Solid-state dewetting and Al facet formation
Hybrid superconductor--semiconductor platforms can host subgap electronic excitations such as Andreev bound states (ABSs); in topological regimes, a special zero-energy class, Majorana bound states (MBSs), can emerge. Here we report the growth of epitaxial Al films by molecular-beam epitaxy on $\mathrm{In_{0.75}Ga_{0.25}As}$ under near-room-temperature substrate conditions. Using a combination of AFM/SEM, cross-sectional TEM, and \emph{in situ} RHEED, we map how substrate temperature and Al deposition rate govern film morphology, continuity, and interface quality. We identify a growth window that yields continuous, superconducting Al films with an abrupt $\mathrm{Al}/\mathrm{In_{0.75}Ga_{0.25}As}$ interface and no detectable indium interdiffusion. We further investigate the thermal stability of these films under \emph{in situ} post-growth heating and \emph{ex situ} annealing following surface oxidation. For unoxidized Al, rapid surface diffusion triggers solid-state dewetting at approximately $165\,^\circ\mathrm{C}$, resulting in the formation of $\{111\}$-faceted Al islands. In contrast, the presence of a native oxide largely suppresses dewetting, with failure occurring only locally at surface defects. Annealing above the indium melting point ($156.6\,^\circ\mathrm{C}$) induces significant In surface migration in both cases, leading either to localized interfacial In inclusions beneath Al agglomerates or to uniform surface contamination at sites of localized layer breakdown. Together, these results define growth and annealing conditions for thermally robust epitaxial Al on III--V semiconductors and provide practical guidance for fabricating high-quality superconductor--semiconductor hybrid platforms for quantum devices.