In this work we present the results of theoretical calculations and experimental studies carried out for Si/Si(1-X)AGe(X): Er/Si heterostructures that show promise as the material for realizing a laser with Si: Er active medium. Analysis of the mode composition and estimation of the degree of electromagnetic wave localization in Si/Si1-XGeX: Er/Si waveguide structures have been performed for a fairly wide range of values of the Si1-XGeX: Er layer thickness and Ge content. It is shown that a method of sublimation molecular-beam epitaxy in germane gas atmosphere enables growing effective light-emitting structures of Si/Si1-XGeX: Er/Si with the external quantum efficiency to 0.2%. The kinetics analysis of erbium photoluminescence, performed for the test structures, demonstrates the appearance of the population inversion of Er3+ ion states under optical pumping. The number of Er ions in the inversely populated state comes to about 80% from the total concentration of optically active Er ions at the excitation power density of 4 W/cm(2). (c) 2005 Elsevier B.V. All rights reserved.