We report the latest results of a continuing study of low pressure‐metal–organic chemical vapor deposition (LP‐MOCVD) growth of InP and Ga0.47In0.53As–InP heterojunctions and superlattices, which describe the general growth of InP and GaInAs with specific application to quantum well heterostructure. A study of the sources and control of residual impurities in InP and Ga0.47In0.53As, the effects of source purity upon residual impurities, mobility, and 2 K PL intensity are detailed. Total impurity concentrations as low as 6×1014cm−3for InP and 3×1014cm−3for Ga0.47In0.53As have been obtained. Mobility as high as=μ (300)=5350, μ (77)=60 000 cm2V−1 s−1for InP, and μ (300)=12 000, μ (77)=60 000, μ (2)=100 000 cm2V−1 s−1for GaInAs layers have been measured.