Silicon carbide epitaxy for power electronics and quantum technology is moving beyond the conventional basal plane. Prismatic surfaces form the sidewalls of trench and superjunction devices, and they improve photon extraction from colour centres. Epitaxial layers grown on the four principal orientations of 4H-SiC — Si-face (0001), C-face (000-1), a-plane (11-20) and m-plane (1-100) — differ strongly in surface morphology, in nitrogen and aluminium incorporation, and in carbon-vacancy concentration, but the underlying mechanism is not established. This limits the control of doping and defect density in trench-filled device structures. Our analytical modelling of the surface crystallography predicts systematic differences between the polar and non-polar orientations, but it requires first-principles input to become quantitative. This project will use density functional theory to determine how substrate orientation controls growth and impurity incorporation in 4H-SiC. We will compute surface energies for the four orientations as a function of carbon chemical potential, adatom migration barriers governing surface diffusion, and formation energies of substitutional nitrogen and aluminium and of the carbon vacancy at and below the surface. The results will be compared directly with epitaxial layers grown on all four orientations under identical conditions, and are intended to provide a predictive basis for selecting growth orientation and conditions in SiC device fabrication.