Strain effects in highly lattice-mismatched InAs0.6P0.4/InP modulation-doped single quantum wells were investigated by the high-resolution transmission electron microscopy (HRTEM), the selected-area electron diffraction pattern (SADP), and the Raman scattering spectroscopy measurements. The HRTEM and the SADP measurements on the InAs0.6P0.4/InP single quantum wells showed that the InAs0.6P0.4 active layer was grown pseudomorphologically on the InP buffer layer in spite of highly lattice mismatch. The values of the horizontal and vertical strains and the horizontal stress of the InAs0.6P0.4 layer are - 1.9 x 10(-2). 2.1 X 10(-2). and - 16.26 X 10(-2) dyne cm(-2), respectively. A possible crystal structure for the InAs0.6P0.4/InP single quantum well is presented based in the HRTEM and the SADP results. These results can help improve understanding the microstructural properties of strained InAsxP1-x/InP modulation-doped single quantum wells.