Control of defect structure in compound semiconductors with stoichiometry: Oxygen inCdTe

Abstract

Two types of localized vibrational modes of oxygen substituting for Te in CdTe, i.e., O Te , are reported. In one, O Te is associated with a nearest neighbor ͑NN͒ vacancy as a ͑O Te -V Cd ͒ center and hence with C 3v symmetry, with its uniaxial axis along ͗111͘, whereas in the other, O Te is surrounded by all the four NN Cd's and thus possesses T d site symmetry. By an appropriate control of stoichiometry it is possible to reproducibly generate the formation of either ͑O Te -V Cd ͒ or O Te centers. These configurations are deduced from their ultrahigh resolution infrared signatures. For the ͑O Te -V Cd ͒ centers, consistent with their uniaxial symmetry, a pair of sharp local vibrational modes ͑LVM͒ are observed at 1 = 1096.78 cm −1 and 2 = 1108.35 cm −1 , the latter nearly twice as intense as the former. In the LVM spectrum of O Te centers with the full complement of NN Cd's, consistent with its T d symmetry, only one LVM signature appears at 0 = 349.79 cm −1 . With the increasing temperature, 1 and 2 approach each other and coalesce into a single triply degenerate line at 0 * for temperature T Ն T * ϳ 300 K; the uniaxial ͑C 3v ͒ symmetry of ͑O Te -V Cd ͒ transforms to T d symmetry at T * and above, acquired by the ͑O Te -V Cd ͒ centers due to the increasing rate of bond switching among the four possible O Te -V Cd ͗111͘ directions as T approaches T * . The ͑O Te -V Cd ͒ centers also display a fascinating pair of second harmonics including a coalescence at T * and beyond.

A tale of two vacancies

“…We next calculated the LVM of O Te using the supercell: Cd 4 Te 3 O. The resultant frequency of 331.86 cm −1 is smaller by ∼ 4% than the experimental value of 345 cm −1 reported by Chen et al [8] and is consistent with the theoretical value of 341 cm −1 obtained by Zhang et al…”

“…Our results suggest that the vibrational frequency of an O 2 molecule may be high enough to explain the high LVM frequencies observed experimentally by Chen et al [8]. Normally O 2 molecules are expected to dissociate in CdTe to form substitutional oxygen.…”

“…We will try to explain within our model the merging of the two LVM peaks into one at ∼ 300 K observed by Chen et al [8]. From their data they deduced an approximate activation energy of ∼ 42 meV for the tunneling process.…”

“…Since O is much lighter than both Cd and Te, O can be detected with great precision by measuring its local vibration modes (or LVM) via far-infrared absorption. Chen et al [8] reported such a study of O doped CdTe at low temperature (T) with very high spectral resolution. However, in addition to the expected LVM of O Te (at 349.8 cm −1 ), they also observed two very sharp absorption peaks which they attributed to LVMs associated with a complex of a O Te and a neighboring Cd vacancy (O Te -V Cd ).…”

Lyman spectra of holes bound to Cu, Ag, and Au acceptors in ZnTe and CdTe

“…Apart from the non-stoichiometric incorporation of cations or anions or both, resulting in vacancies and interstitials, there are major residual impurities that can dominate optical and electrical properties of these materials [6][7][8] . Their occurrence limits their applications in X-ray and γ-ray detectors and solar panels [9][10][11][12][13] .…”