It is well known that crystal growth and defect propagation occur along the local thermal gradient at a liquid - solid interface, It is shown here that this property can be used to greatly reduce the density of structural defects in zone crystallized silicon thin films on amorphous substrates, A solidification front perpendicular to the direction of zone motion has its in - plane component of the thermal gradient parallel to the direction of zone motion. In this case, the defects, once nucleated, propagate along this zone path and the defect density reaches a steady state value. By using striped polysilicon patterning and a solidification front tilted relative to the molten zone path, a defect-free region is shown to occur. It is also shown that defects, once nucleated, are swept laterally from the region of interest and are terminated at the stripe boundary Methods of forming a tilted interface are proposed and demonstrated for CO2 laser crystallization.