In this work, we report on the effect of adding GeH 4 during 3C-SiC heteroepitaxial growth on low off-axis 4H-SiC substrate using chemical vapor deposition technique. When added together with SiH 4 and C 3 H 8, GeH 4 does not significantly modify the 3C layer quality which contains a high density of twin boundaries. But when it is introduced before the growth, ie during a surface pretreatment step at 1500 C, a remarkable change in the layer morphology is seen. Furthermore for optimal GeH 4 flux, twin boundaries are completely eliminated. Investigation of the results obtained when varying growth parameters (temperature, C/Si ratio, gas composition during the surface preparation) allowed proposing a mechanism leading to twin boundary elimination. It involves a transient homoepitaxial growth step followed by 3C nucleation when large terraces are formed by step faceting. Preliminary electrical characterizations …