PbTe/Pb1-xEuxTe superlattices of various PbTe well thicknesses were prepared on thick PbTe buffers grown on KCl(100) substrates. Optical transmission spectra of the superlattices were measured in the temperature range of 77 to 300 K. Clear step-like absorptions corresponding to electron transitions between valence and conduction subbands (n = 1, 2, 3 to n = 1, 2, 3) were observed even at 300 K up to a PbTe well thickness of 180 Å: The steps in the absorption coefficients became unclear with the increase in the superlattice period or PbTe well thickness as the result of a restriction by the mean free path of the electron. The abruptness of the steps increased rapidly with decreasing temperature, owing to the increase of the mean free path. Theoretical calculations using the envelop-function approximation were performed assuming that effective masses of the PbTe and Pb1-xEuxTe are proportional to the energy band gap. Experimental absorption edges and their temperature dependence agreed well with the theoretical values calculated assuming that the conduction band off-set is equal to that of the valence band. © 1988.
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