Alloy composition shift and control during Cl-assisted metalorganic vapor phase epitaxial (MOVPE) growth was investigated. Tertiarybutylchloride (TBCl) was used as a chlorine gas source. In situ ellipsometry observation of the InGaAs growth clearly indicated that the introduction of TBCl affects the composition of the alloy as well as its growth rate. The reduction in growth rates of binary compounds follows the order InP > InAs > GaAs (1:0.64:0.13) at about 620 degreesC on the (001) surface. Applying the above result to compensate the compositional shift of InGaAs due to the TBCl introduction, we could successfully grow lattice-matched InGaAs/InP by Cl-assisted MOVPE with TBCl. X-ray diffraction and photoluminescence spectra showed that the addition of TBCl did not affect InGaAs crystallinity. (C) 2002 Elsevier Science B.V. All rights reserved.