Numerous applications require the growth of planar strained-layer heterostructures on relaxed Si1-xGex. After briefly reviewing these applications as well as the challenges in growing such heterostructures, we provide experimental examples illustrating the influence of lattice mismatch, growth temperature, and film composition on the morphology of thin strained layers in the Ge-Si alloy system. Procedures for growing strained Si and strained Ge single and double hetero structures via ultrahigh vacuum chemical vapor deposition are described in detail. We demonstrate planar growth of strained Ge layers with lattice mismatches as high as 2%, planar Si layers on any Si1-xGex lattice constant, and double heterostructures that are comprised of a strained Ge layer capped with strained Si. Notably, the techniques described here have already been applied to the fabrication of extremely high mobility p- and n-channel metal-oxide-semiconductor field-effect transistors and germanium-on-insulator substrates. (C) 2004 American Vacuum Society.