Local vibrational modes of substitutionalMg2+,Ca2+<

Abstract

Localized vibrations of substitutional Mg +, Ca +, and S in CdTe, ZnTe, and CdSe are observed as sharp absorption lines in the infrared and display as many lines as there are isotopes of the impurity, their intensities being proportional to their natural abundances. The lowering of the site symmetry from T& in the zinc-blende CdTe and ZnTe to t 3 in the wurtzite CdSe causes the triply degenerate (I' s) mode in the former to split into a singlet (I'q) and a doublet (I' s) in the latter, the singlet and the doublet appearing only for the electric vector along the optic axis and normal to it, respectively. The features of the local mode are interpreted in terms of an anharmonic oscillator consistent with the site symmetry of the impurity. The evolution of the Mg + local mode from that in CdTe to that in ZnTe, as observed in a series of Mg doped Cdq Zn Te samples, provides insights into the variation of the local mode frequency or, equivalently, the Mg-Te force constant in the context of virtual crystal approximation. Their linewidths, however, can be correlated with the x(lx) disorder in the ternary. Ultrahigh resolution measurements of the Mg + local mode in ZnTe and CdSe reveal 6ne structures originating in the isotopic disorder of the nearest neighbor Te and Se, respectively.

Stoichiometry Driven Impurity Configurations in Compound Semiconductors

“…This difference could well be attributed to the additional dynamic switching associated with 1 and 2 . Neither 1 and 2 nor 0 exhibit, even under the highest resolution and at the lowest temperature, the ''host isotopic effect'' shown by Mg 2 in CdTe [2], presumably due to the significantly lighter oxygen relative to Cd.…”

“…In order to accomplish this, we grew CdTe with the addition of CdO but with excess Cd to provide O, on the one hand, and to suppress vacancies, on the other, and thus create conditions conducive to the formation of centers of oxygen with four Cd's surrounding it. From the knowledge of the LVM of S Te in CdTe [2], we estimated the spectral range in which to explore the occurrence of the LVM of O Te to be between 325 and 375 cm ÿ1 . As can be seen in Fig.…”

“…Spectroscopic signatures of point defects serve as insightful characterizations in basic studies and applications. In this context, localized vibrational modes (LVM) revealed in their infrared absorption spectra, for example, provide invaluable information into the nature of the defect as well as of the host [1,2].…”

Isotope splitting of the zero-phonon line of Fe2+ in cubic III–V semiconductors

“…Work on the effects of isotopic composition includes the discovery of the enhancement of the thermal conductivity of isotopically enriched Ge relative to that of natural Ge [3], the measurement of isotopic effects on the lattice parameter of Ge [4] and diamond [5] and the dependence of the frequency of the zone center F 2g (Γ 25 + ) optical mode on the inverse square-root of the mass observed in the Raman spectrum of monoisotopic Ge [6,7] and diamond [8]. More recently, the effects of the anharmonicity of the lattice vibrations and of the zero-point motion of the atoms have been observed and analyzed in natural and 13 C-enriched diamond [9,10]. Reviews of some aspects of these topics have been given by Ramdas [11] and Haller [12].…”

“…We mention, for example, the determination of the frequencies of the local vibrational modes (LVM) of light impurities substituting for either the group II or VI host atom in a II-VI semiconductor and their dependence on isotopic composition [13,14]. The LVM of transition metal ions of the iron group substituting for the cations at random sites in II-VI semiconductors having the zinc-blende structure have also been observed by Mayur et al [15] in infrared absorption with as many lines as there are isotopes of the impurity and with intensities proportional to their natural abundances.…”