Low-defectivity, compressively strained Ge on Si0.2Ge0.8 was fabricated in oxide trenches using the aspect ratio trapping technique. This was accomplished through the use of pre-epi bakes optimized to remove interfacial impurities which can lead to defective epi layers. Pre-epi bake over the optimum temperature caused the release of stored elastic strain energy in the Si0.2Ge0.8 regions leading to undesirable undulations of the layers. Using the optimum prebake at 810 degrees C, 42 nm thick, compressively strained Ge was grown. It had 1 and 0.45% elastic strain along and perpendicular to the trench direction, respectively, which is well-suited for strained Ge channels in future complementary-metal-oxide semiconductor devices.