The optical properties of tensile strained In1-xGaxAsyP1-y/InP single quantum wells grown by low-pressure metalorganic vapor phase epitaxy were investigated by the real-time integrated photoluminescence microscopy imaging technique at room temperature. The photoluminescence microscopy images revealed the presence of a large number of nonradiative centers (dark spots). The dark spot density was found to be strongly dependent on the tensile strain magnitude, barrier type material and cap layer thickness. High tensile strain values and thin InP cap layers resulted in an increased density of dark spots. Tensile strained structures employing lattice-matched quaternary barriers instead of InP barriers exhibited reduced defect density. Our results indicate that these defects are mainly localized close to or at the interface between the quaternary well and the upper barrier material. The reduction of the number of defects correlates quantitatively with increased radiative recombination efficiency in these structures. © 1999 American Institute of Physics.