[en] An attempt has been made to explain the gross features of low-energy X-ray spectra including background, peak tailing, peak shift and dispersion for Si(Li) and HPGe detectors, analytically. The principal contributing physical effects are established and the fundamental limits of detector performance indicated. Calculations have been made to estimate the spectral contribution of escaping primary and secondary electrons from and to the detecting medium and the results are compared with data taken from a large number of detectors using an ⁵⁵Fe source and an SEM as well as from individual detectors with a monochromatic 5.9 keV X-ray source