Ellipsometry: a technique for real time monitoring and analysis of MBE-grown CdHgTe and CdTe/HgTe superlattices

Ellipsometry is a sensitive non-destructive analytical technique well suited to the MBE growth process. We report its use in real time to control CdHgTe alloy composition, to control growth of superlattice structures, and to provide a measure of growth-related defect phenomena. A Riber 32 R&D MBE machine has been custom modified by the manufacturer to facilitate the addition of a phase-modulated ellipsometer and we report here the results of measurements on CdHgTe and CdTe/HgTe superlattices grown on CdTe and Cd 0.96Zn 0.04Te (100) substrates. Growth rate data from ellipsometry are in good agreement with RHEED intensity oscillation data, double-crystal rocking curve determinations of superlattice periodicity, and IR transmission measurements of total thickness. The level of Hg incorporation in CdTe (100) superlattice layers is readily detected and its temperature dependence is established. Growth-front roughening during the growth of the CdTe layers limits the abrupt nature of the interface. These results are compared with model calculations and a compositional profile of these interface structures is proposed.