Single- and multiple-quantum well (QW) nanophotonic devices, such as detectors and solar cells, are often fabricated by the concatenation of low-dimensional heterojunctions of different semiconductors. Quantum effects dominate the well structure, with dimensions of the order of several nanometers. At this width regime, even small variations in the fundamental material properties, such as band gap, dielectric constant, lattice constant, and effective mass of the materials, may give rise to errors in determining the fundamental design parameters. This, in turn, can significantly affect the device performance. In cadmium-sulfide/cadmium-telluride (CdS/CdTe) material system, the failure to include the mismatch of electronic effective masses can lead to <30% shift from the real position of the eigenstate energy levels, and <40% shift from the real position of quasi-Fermi levels E Fn and E Fp . In addition, depending on the width of the QW active layer, the absorption coefficient value can lead to <12% shift from its real value. These results prompt the need for accurate estimation of such errors in the precise analysis and design of CdS/CdTe heterojunction-based nanophotonic devices.