Te Antisite Defects Research Articles

Assessment of intrinsic and doped defects in Bridgman grown Cd1-xZnxTe alloys

A comprehensive experimental and theoretical study is presented to empathize the dynamical properties of Bridgman grown Cd1-xZnxTe samples. Low temperature Raman scattering study has offered an excellent testimony to the lattice phonons of the perfect alloys with a strong evidence of Te anti-site defect (TeCd) modes. An average transfer matrix (ATM) Green’s function (GF) method is employed to examine the isotopic shifts of localized vibrational modes (LVMs) of isolated oxygen OTe defects in CdTe and the low frequency A1 and E phonon modes of TeCd. For the nearest-neighbor (NN) OTe – VCd pair, while the ATM-GF’s study revealed quite different values of LVMs from the existing infrared (IR) absorption data – the results, however, provided good justification to a simple perturbation relationship of 16OTe isotopic mode. An excellent agreement between theory and IR data of impurity modes has validated the formation of NN donor–acceptor pairs and next-nearest-neighbor complex centers involving intrinsic defects. The study is important not only for empathizing the growth process of technologically important Cd1-xZnxTe alloys but also identifying the role of carrier compensation mechanism by various donors and acceptors.

Concurrent defects of intrinsic tellurium and extrinsic silver in an n-type Bi2Te2.88Se0.15 thermoelectric material

We suggested a defect system consisting of Te- and Ag-related defects in n-type Bi2(Te,Se)3. We prepared the Te-rich Bi2Te2.88Se0.15 compound, which is expected to have Te antisite defects, via a conventional pulverization process. We devised a one-pot chemical process in which Ag nanoparticles were synthesized and instantly deposited onto the Bi2Te2.88Se0.15, followed by spark plasma sintering; thus, Ag atoms were inserted into the lattice structure of the Bi2Te2.88Se0.15 during the sintering process. Atomic layers of the Bi2Te2.88Se0.15 were resolved by transmission electron microscopy and dark-field scanning electron microscopy imaging with energy dispersive X-ray spectroscopy; the Ag atoms were thereby proven to occupy the interstitial sites in the Bi2Te2.88Se0.15 (i.e., Ag interstitial defects). The defect system composed of the Te antisites and Ag interstitials decoupled the electrical properties of the Bi2Te2.88Se0.15 from its thermal properties. We endeavored to adjust the defect system to maximize the decoupling effect, which resulted in the preeminent average figures of merit for operation below 150 °C (ZTave = 1.22 at 25–100 °C and 1.18 at 25–150 °C) among n-type Bi2(Te,Se)3 materials.

125Te NMR and Seebeck Effect in Bi2Te3 Synthesized from Stoichiometric and Te-Rich Melts

Bi2Te3 is a well-known thermoelectric material and, as a new form of quantum matter, a topological insulator. Variation of local chemical composition in Bi2Te3 results in formation of several types of atomic defects, including Bi and Te vacancies and Bi and Te antisite defects; these defects can strongly affect material functionality via generation of free electrons and/or holes. Nonuniform distribution of atomic defects produces electronic inhomogeneity, which can be detected by 125Te nuclear magnetic resonance (NMR). Here we report on 125Te NMR and Seebeck effect (heat to electrical energy conversion) for two single crystalline samples: (#1) grown from stoichiometric composition by Bridgman technique and (#2) grown out of Te-rich, high temperature flux. The Seebeck coefficients of these samples show p- and n-type conductivity, respectively, arising from different atomic defects. 125Te NMR spectra and spin–lattice relaxation measurements demonstrate that both Bi2Te3 samples are electronically inhomogeneo...

Tailoring of defect levels by deformations: Te-antisite in CdTe

The properties of the Te-antisite defect in the neutral state in CdTe were examined using ab initio calculations. The influence of three types of deformations (1D, 2D and 3D) on the defect energy levels and formation energies was investigated. It was found that the 2D deformation is the most effective for pushing the defect levels towards the band edges and opening up the bandgap of the semiconductor, and hence may improve the performance of CdTe as a detector material. We studied the defect levels and their occupancies including Jahn–Teller distortions. The Jahn–Teller distorted configuration places the defect level closer to the valence band and this defect level position coincides with the ‘unknown deep donor’ measured in some experiments. Partial densities of states and band structures have been analysed to understand the arrangement of the defect bonds.

Influence of the cooling scheme on the performance and presence of carrier traps for CdMnTe detectors

The detector performance and presence of Te secondary-phase defects distribution were investigated in CdMnTe (CMT) crystals prepared with different cooling rates. Detectors fabricated from fast-cooled CMT crystals exhibit a relatively poor detector performance, although IR transmission microscopy measurements show that the Te secondary-phase defects have a lower concentration and smaller size compared to slow-cooled crystals. Current deep-level transient spectroscopy (I-DLTS) measurements for both CMT detectors reveal the same trap levels, but there is a clear difference in the densities for the 0.26- and 0.42-eV traps for the two different cooling schemes. These two traps are probably attributed to Cd vacancies and Te anti-site defects, respectively. In addition, there is some likelihood that the traps are anti-correlated with respect to each other.

Hydrogen–Te antisite complex impurity (H–TeHg) in Hg0.75Cd0.25Te: First-principles study

Using first-principles method within the framework of the density functional theory, we study the formation energies and the binding energies of hydrogen–telluride antisite complex impurities (n H–TeHg, n=1,2) in Hg0.75Cd0.25Te. We find that telluride antisite impurity (TeHg) in Hg0.75Cd0.25Te is a double donor. When Te antisite and an interstitial hydrogen move close to each other, the interaction between them leads to the creation of a stable 1H–TeHg complex with a binding energy of 0.33eV. In this case, the donor effects induced by Te antisite are partially passivated. As the hydrogen concentration increases, the binding energy of the 2H–TeHg forming from combining H–TeHg with interstitial hydrogen is only 0.005eV. Namely, 2H–TeHg is unstable in Hg0.75Cd0.25Te and hydrogenation cannot fully neutralize Te antisite defects.

Electrical and thermal transport properties of electrically stressed Bi–Sb–Te nanocrystalline thin films

Nanoscale size effect is beneficial for enhancing thermoelectric figure-of-merit of Bi–Sb–Te compounds due to the decrease of thermal conductivity. Bi–Sb–Te nanocrystalline thin films prepared by sputtering at room temperature, in general, require a post-deposition treatment to improve their electrical transport properties by eliminating residual crystal defects. In this study we present an electric current stressing treatment to effectively eliminate crystal defects in sputtered Bi–Sb–Te films at low temperature. By maintaining a low thermal conductivity of 0.6–0.7 W/mK, the electrically stressed Bi–Sb–Te nanocrystalline films possess highly enhanced Hall mobility and moderately reduced carrier concentration as compared to the films thermally treated at the same temperature. Carrier concentration, mobility and Seebeck measurement results suggest that the change of electrical transport properties involves the elimination of Sb Te antisite defects as supported by the observation of some Sb-rich precipitates in the thermally/electrically treated Bi–Sb–Te films. Besides, crystal defects are also suggested to be preferentially removed in the (00 l)-oriented grains due to anisotropic diffusion and electrical transport properties in the electrically stressed Bi–Sb–Te films.

Modified compensation model of CdTe

The traditional compensation model to explain the high resistivity properties of CdTe is based on the presence of a deep acceptor level of the cadmium vacancy in the middle of the band gap. A new compensation model based on a deep intrinsic donor level is presented. The compensation model is used together with an appropriate segregation model to calculate axial distributions of resistivity which are compared with spatially resolved resistivity measurements. The Te-antisite defect is discussed as a possible origin cause of this intrinsic defect, which is also supported by theoretical calculations.

CdTe II: Defect chemistry

A statistical thermodynamic derivation of the equilibrium equations for two defect models for CdTe(s) at high temperatures is given. In the first the predominant defects are assumed to be doubly ionizable Cd vacancy acceptors and singly ionizable Te antisite donors in Te rich material and doubly ionizable Te vacancy donors in Cd rich material. A variant in which the Te antisite defect is neutral is readily extracted from the equations by setting the donor level far enough below the conduction band edge. In the second model the Te antisite defect is replaced by a neutral Te interstitial defect. The models are then applied to the high temperature data. It is concluded that the singly ionizable Te antisite model gives the best overall fit and various high temperature properties are calculated with two sets of the adjustable parameters.

Point Defects in Sn‐Doped Sb2Te3 Single Crystals

AbstractSingle crystals of Sb2Te3 doped with 0 to 1.0 at% Sn are prepared and the Hall coefficient, Seebeck coefficient, and plasma resonance frequency of the crystals are determined. The incorporation of one Sn atom into the Sb2Te3 crystal corresponds to an origin of ≈ 2.2 to 3.0 holes. Such an increase in the concentration of holes is explained in terms of a decrease in the bond polarization due to the incorporation of negatively‐charged Sn'Sb defects into the Sb sublattice which is favourable for the formation of antisite defects in Sb2Te3. The observed increase in the hole concentration corresponds to the sum of created Sn'Sb defects and newly formed Sb'Te antisite defects in Sn‐doped Sb2Te3.