We have investigated the effects of Yb addition to melts used for the growth of InGaAs/InP heterostructures by liquid phase epitaxy. Our results indicate that impurities in the Yb play an important role in determining the changes in electrical properties observed in the epilayers after Yb treatment of the melt. We have examined samples using double-crystal x-ray diffractometry, photoluminescence, Hall/van der Pauw measurements, and secondary-ion mass spectroscopy. After Yb treatment, the residual carrier concentrations of the epilayers were reduced by more than one order of magnitude and the samples luminesced more strongly; while the lattice matching and crystal quality of the epilayers were not measurably affected by the Yb. There was a smaller-thanexpected ncrease in the 77K mobility and a marked increase in the compensation ratio of the epilayers grown after the addition of Yb to the melt. We believe the Yb is both acting as a scavenging agent in the melt, combining with impurities that otherwise would have been incorporated in the epilayers, and introducing deep level impurities of its own, which are incorporated into the grown layers.