ABSTRACTDifferent III-V compound semiconductors have been doped with the rare earth (RE) elements Yb, Er, and Tm using atmospheric pressure metalorganic vapor phase epitaxy. Best results have been obtained using the novel metalorganic compounds tris-isopropyl-cyclopentadienyl-RE as precursors which have an acceptable vapor pressure and can be used as liquids at bubbler temperatures of 60°-90°C. Only Yb has been found to occupy a regular lattice site in InP, whereas the other RE show complex optical spectra because of their incorporation in form of different centers and clusters.