Epitaxial wafers showing marked IG effects can be manufactured from silicon single crystals doped or not doped with nitrogen without requiring any additional heat treatment process step while reducing the density of epitaxial layer defects. The latter supports a cam that is moveably engageable with the stem member, movement of the cam determining the part thereof that engages the stem member in order to cause the stem member and the indexing mount to pivot one relative to the other in adjustment of their relative translational positions. The first physical layer header may span a first length and represent a first modcode; the second physical layer header may span a second length and represent a second modcode.