Quantitative interfacial profiles in CdTe/Mn(Mg)Te heterostructures

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Abstract
We have measured by high resolution transmission electron microscopy (HRTEM) the width of interfaces in two II–VI heterostructures: CdTe/MnTe and CdTe/MgTe, as a function of the growth mode. A critical review of the different parameters involved in the direct determination of the chemical profile by HRTEM enables us to precisely determine the sensitivity and accuracy of the methods on these particular materials. The measured interface width is of the order of 2.5–3 monolayers (ML) and is compatible with an exchange mechanism involving the monolayer being grown and the last deposited monolayer. Several growth procedures were compared: conventional molecular beam epitaxy and atomic layer epitaxy (ALE). In the case of saturated and oversaturated ALE the inverse MnTe/CdTe interface is no longer planar. A destabilization of the growth front occurs when one or more Mn monolayers per cycle are deposited, through the formation of MnTe islands. Thermal interdiffusion seems to be negligible in the case of Mn. The present HRTEM values for the interface widths extend the results obtained by magneto-optical measurements to higher concentration values and confirm the exchange mechanism. The higher value obtained by x-ray reflectivity (4.7 ML) is explained by the large difference of the average volume on which the measurement is performed.