We study coalescence defects and their possible origins for Ge growth within parallel SiO2 trenches created on (001) Si along [110] and [100] directions and (001) Ge substrates along [110]. Prior to coalescence, defects are not observed at the top of Ge, emerging from within trenches during lateral growth over the SiO2 template. However, for Ge on Si growth, coalescence of Ge growing from adjacent trenches leads to twin defects and threading dislocations that originate from the top center and top corners of the SiO2 walls, respectively. For Ge-on-Ge homoepitaxy, twins and threading dislocations are observed in Ge above the top center of the SiO2, but dislocations are not observed at the top corners of the SiO2 walls. The twin defects are preferentially aligned along the same direction as channels patterned along [110] (twin density of 1.5 x 10(7) cm(-2)), but not for channels patterned along [100] (twin density of 2.5 x 10(7) cm(-2)). Finite element modeling is used to calculate the thermal stresses occurring in Ge and reveals that maximum thermal stress occurs near the top corners of the SiO2 walls, where the threading dislocations (density of 7.2 x 10(7) cm(-2)) are experimentally observed in Ge grown on Si. (C) 2011 Elsevier B.V. All rights reserved.