The disclosed technology generally relates to complementary metal-oxide-silicon (CMOS) devices, and more particularly to a transistor device comprising a germanium channel layer, such as an n-channel metal-oxide-silicon (NMOS) transistor device. In one aspect, a method of forming a germanium channel layer for an NMOS transistor device comprises providing a trench having sidewalls defined by a dielectric material structure and abutting on a silicon substrate's surface, and growing a seed layer in the trench on the surface, where the seed layer has a front surface comprising facets having a (111) orientation. The method additionally includes growing a strain-relaxed buffer layer in the trench on the seed layer, where the strain-relaxed buffer layer comprises silicon germanium. The method further includes growing a channel layer comprising germanium (Ge) on the strain-relaxed buffer layer. In other aspects, devices, e.g., an NMOS transistor device and a CMOS device, includes features fabricated using the method.