Significant effort in compound semiconductor device growth centers on control of strain in the trtulti-component alloys. thus, the ability to measure layer strain during the growth process is highly desirable. We have developed an instrument to measure strain in situ during the MOCVD growth process on rotating disk reactors. Excellent qualitative and quantitative agreement was observed between in situ and ex situ determined strain values. Strain agreement within 100 ppm was commonly observed on AlGalnAs layers nearly lattice matched to InP substrates. We demonstrate the ability to intelligently adjust layer strain during growth and show the importance of layer strain control on AlGalnAs/InP distributed Bragg reflector surface morphology and optical reflectance performance. (C) 2003 Elsevier B.V. All rights reserved.