A direct growth approach using composite metamorphic buffers was employed for monolithic integration of InP-based high electron mobility transistors (HEMTs) and heterojunction bipolar transistors (HBTs) on Ge and Ge-on-insulator (GeOI)/Si substrates using molecular beam epitaxy. GaAs layers nucleated on these substrates and grown to a thickness of 0.5 mu m were optimized to minimize the nucleation and propagation of antiphase boundaries and threading dislocations, and exhibited an atomic force microscopy rms roughness of similar to 9 A and x-ray full width at half maximum of similar to 36 arc sec. A 1.1 mu m thick graded InAlAs buffer was used to transition from the GaAs to InP lattice parameters. The density of threading dislocations at the upper interface of this InAlAs buffer was similar to 10(7) cm(-2) based on cross-sectional transmission electron microscopy analyses. HEMT structures grown metamorphically on GeOI/Si substrates using these buffer layers demonstrated transport properties equivalent to base line structures grown on InP substrates, with room temperature mobility greater than 10 000 cm(2)/V s. Similarly, double heterojunction bipolar transistors (D-HBTs) grown metamorphically on GeOI/Si substrates and fabricated into large area devices exhibited dc parameters close to reference D-HBTs grown on InP substrates. (C) 2008 American Vacuum Society.