LOCAL AND GAP MODES OF SUBSTITUTIONAL 3D TRANSITION-METAL IONS IN ZINCBLENDE AND WURTZITE II-VI SEMICONDUCTORS

The localized vibrational modes of the 3d transition-metal ions (TMI's ) substituting for the cations in CdTe, ZnTe, and CdSe appear in infra red absorption with as many lines as there are isotopes of the impurit y and with intensities proportional to their natural abundances. The t riply degenerate local mode in a zinc-blende host splits into a single t and a doublet in a wurtzite host, the former appearing only when the electric vector (E) of the incident radiation is parallel to the opti c axis ((c) over cap) and the latter when <E perpendicular to(c)over c ap>. Replacement of Cd by a TMI in CdSe results in high-frequency loca l vibrational as well as gap modes lying in the gap between the acoust ic- and optic-phonon branches, the latter exhibiting an optical anistr opy similar to that of the former. Both the local and the gap modes ex hibit a unique nonmonotonic trend across the 3d transition-metal serie s, with a minimum at Mn.