A consequence of the high energy of the Si-face that it is highly unstable in pure and carbonenriched hydrogen ambient between 1400-1580 °C, which is similar to our experimental conditions. Under these conditions, the Si face tends to be subjected to heavy step-bunching, forming irregular macro steps and micro steps of variable height, as well as etch pits. In contrast, the C-face is reported to be etched smoothly at these conditions forming only micro steps with an average height of 2.5 nm , equivalent to 2.5 times the c-axis of a 4H-SiC unit cell and about twice the c-axis of a r-B4C unit cell (12.065-12.175 Å) . These aspects could explain the different results obtained between the two SiC faces, the etching of the Si-face results in a complex topography, facilitating polycrystalline growth, while the steps after etching the C-face are close to lattice-matched to both the c-and a-axes of the r-B4C unit cell.