The subband dispersion relations have been computed as a function of the surface electron concentration in the accumulation layers ofn-Hg1−xCdxTephotoconductive detectors, while the mobility and concentration for all kinds of carriers in the subband are determined from Shubnikov-de Haas (SdH) oscillation measurements and quantitative mobility spectrum analysis (QMSA). The results show that the QMSA can provide accurate electric parameters for all kinds of carriers in the subband without considering the complex energy band in the semiconductors, while the SdH oscillation can only offer qualitative data because the analysis is based on parabolic energy band approximation. ©1997 American Institute of Physics.