TlGaTe2 Crystals Research Articles

Determination shape of the potential well of traps in TlGaTe2 crystals

The single crystals of TlGaTe2 were grown by the Bridgman method. The current–voltage characteristics were performed for obtained crystals and it was determined that the Poole–Frenkel effect occurs in the nonlinear region of the current in the directions parallel and perpendicular to the crystallographic axis. The calculated values of the concentration of ionized centers [Formula: see text], the mean free path [Formula: see text], the values of the Frenkel coefficient [Formula: see text] and the shape of the potential well in TlGaTe2 crystals are determined.

Ionic conductivity and dielectric relaxation in γ-irradiated TlGaTe2 crystals

The switching effect, field and temperature dependences of the permittivity and conductivity of TlGaTe2 crystals subjected to various γ-irradiation doses are studied. Under rather low electric fields, the phenomenon of threshold switching with an S-shaped current-voltage characteristic containing a portion with negative differential resistance is observed in the crystals. In the region of critical voltages, current and voltage oscillations and imposed modulation are observed. Possible mechanisms of switching, ionic conductivity, disorder, and electrical instability in TlGaTe2 crystals are discussed.

Effect of ionizing radiation on the dielectric characteristics of TlInS2 and TlGaS2 single crystals

The temperature dependences of the electrical conductivity and the permittivity of TlInSe2 and TlGaTe2 crystals unirradiated and irradiated with 4-MeV electrons at a doze of 1016 cm−2 have been investigated. It has been established that electron irradiation leads to a decrease in the electrical conductivity σ and the permittivity ɛ over the entire temperature range under study (90–320 K). It has been revealed that the TlInSe2 and TlGaTe2 single crystals undergo a sequence of phase transitions characteristic of crystals of this type, which manifest themselves as anomalies in the temperature dependences σ = f(T) and ɛ = f(T). Electron irradiation at a doze of 1016 cm−2 does not affect the phase transition temperatures of the crystals under investigation.

Temperature-dependent capacitance–voltage biasing of the highly tunable TlGaTe2 crystals

The temperature effects on the capacitance–voltage characteristics as well as the room temperature capacitance–frequency characteristics of TlGaTe2 crystals are investigated. A very wide range of linearly varying tunable capacitance from 6.0μF to 60pF was recorded. The capacitance–voltage characteristics, being recorded in the temperature range of 290–380K, revealed a linear increase in the build in voltage associated with exponential decrease in the density of non-compensated ionized carriers with increasing temperature. The high temperature (up to 380K) biasing ability, the linear tunability and the high dielectric constant values (∼103) make the TlGaTe2 crystals applicable in microelectronic components.

Superionic Conductivity and Specific Effects Induced by γ-Radiation in Nanofibrous TlGaTe2 Crystals

Temperature dependences of electrical conductivity (T), switching effect, THz spectra and permittivity e(T) of onedimensional (1D) TlGaTe2 single crystals are investigated. The superionic conductivity observed at temperatures above 305 K is related to diffusion of Tl+ ions via vacancies in the thallium sublattice between   2 2 3 Te Ga nanochains. A relaxation character of dielectric anomalies suggests the existence of electric charges weakly bound to the crystal lattice. Upon the transition to the superionic state, relaxors in the TlGaTe2 crystals are Tl+ dipoles ((   2 2 3 Te Ga ) nanochains) that arise due to melting of the thallium sublattice and hops of Tl+ ions from one localized state to another. The effect of a fieldinduced transition of the TlGaTe2 crystal to the superionic state is detected. The temperature dependences of σ(T) and currentvoltage characteristics subjected to various doses of γradiation in both geometries of the experiment, along nanochains parallel to the tetragonal axis of the crystal σ) and perpendicular to these nanochains, are studied. It is shown that the dependence σ(T) measured in the ohmic region of the current-voltage characteristic is the shape typical of the hopping mechanism. The current-voltage characteristics in the region of a more abrupt increase in the current are also studied and explained in the context of the Pool-Frenkel thermal-field effect. It is shown that anisotropy of electrical conductivity changes under the effect of irradiation, which brings about translational ordering of nanochains. Terahertz time-domain spectroscopy reveals absorption lines at approximately 0.2 THz that may be attributed to the libration oscillations of the nanofibers in the superionic phase.

Superionic conductivity in TlGaTe2 crystals

Temperature dependences of electrical conductivity σ(T) and permittivity ɛ(T) of one-dimensional (1D) TlGaTe2 single crystals are investigated. At temperatures higher than 305 K, superionic conductivity of the TlGaTe2 is observed and is related to diffusion of Tl+ ions via vacancies in the thallium sublattice between (Ga3+Te22−− nanochains. A relaxation character of dielectric anomalies is established, which suggests the existence of electric charges weakly bound to the crystal lattice. Upon the transition to the superionic state, relaxors in the TlGaTe2 crystals are Tl+ dipoles ((Ga3+Te22−)− chains) that arise due to melting of the thallium sublattice and hops of Tl+ ions from one localized state to another. The effect of a field-induced transition of the TlGaTe2 crystal to the superionic state is detected.

Giant dielectric relaxation in TlGaTe2 crystals

The conductivity and temperature-frequency dependences of the permittivity of TlGaTe2 crystals have been studied. Strong dielectric relaxation has been revealed. It has been shown that the mechanism of dielectric relaxation is associated with hopping of Tl ions over vacancies in the thallium sublattice due to the transition of the system to the superionic state.

Superionic Conductivity in One-Dimensional Nanofibrous TlGaTe2 Crystals

We study the temperature dependence of the electrical conductivity σ(T) of TlGaTe2 crystals under an electric field (E = 181 V/cm). A strong sharp increase (×1500) in σ(T) is observed at T = 242 K (along the c-axis) and T = 267 K (perpendicular to it). This increase is attributed to a transition towards a superionic conductivity behavior. Over the superionic transition threshold, disordering of the Tl+ sublattice in TlGaTe2 occurs, and nanoscale topological disordering arises owing to aperiodicity in placing Ga3+Te22- nanofibers. Terahertz time-domain spectroscopy reveals absorption lines at approximately 0.2 THz that may be attributed to the libration oscillations of the nanofibers.

Temperature dependence of dielectric function and optical transitions in TlInSe2 and TlGaTe2

The principal components of the dielectric function of TlInSe2 and TlGaTe2 crystals with quasi-one-dimensional chain structure have been studied over the photon energies 1.5–5.0eV in the temperature range 140–400K, with due regard to the reported phase transitions. For TlGaTe2, the absolute values of the dielectric function experience a sudden temperature-induced change at 290K in nearly all the accessed photon energy range. The energy and other parameters of the critical points for inter-band optical transitions related to the obtained dielectric function have then been retrieved for both TlInSe2 and TlGaTe2. An abrupt change in the energy of the critical point, positioned at 2.93eV at room temperature and formed by optical transitions induced by the light polarized along the chains, has then been disclosed for TlGaTe2 at 290K.

Specific features of conductivity of γ-irradiated TlGaTe2 crystals with nanochain structure

Temperature dependences of electrical conductivity σ(T) and current-voltage characteristics of one-dimensional TlGaTe2 single crystals subjected to various doses of γ-ray radiation in both geometries of the experiment-along nanochains parallel to the tetragonal axis of the crystal (σ|) and perpendicular to these nanochains (σ⊥)-are studied. It is shown that the dependence σ(T) measured in the ohmic region of the current-voltage characteristic is the shape typical of the hopping mechanism and can be described in terms of the Mott approximation. The values of the densities of localized states NF, the activation energy Ea, the hop lengths R, the difference between the energies of states ΔE in the vicinity of the Fermi level, and the concentrations of deep traps Nt are determined. The current-voltage characteristics in the region of a more abrupt increase in the current are also studied. It is shown that this region of current-voltage characteristics is described in the context of the Pool-Frenkel thermal-field effect. Concentrations of ionized centers Nf, the free-path lengths λ, the Frenkel coefficients β, and the shape of the potential well in initial and irradiated (with 250 Mrad) TlGaTe2 crystals are determined. It is shown that anisotropy of electrical conductivity changes under the effect of irradiation, which brings about translational ordering of nanochains.

Thermal Expansion and Isothermal Compressibility of TlGaTe2

TlGaTe2 crystals were characterized using x-ray diffraction, and their thermal expansion and isothermal compressibility were measured from 77 to 400 K. The results indicate that TlGaTe2 undergoes a second-order phase transition at 98.5 K.

Growth and Characterization of Single Crystals of the Ternary Compound TlGaTe2

AbstractThe electrical conductivity and the Hall effect for TlGaTe2 crystals have been measured over a wide temperature range. The crystal used for our study was grown by the Bridgman technique and possessed p‐type conductivity. The energy gap has been found to be 0.84 eV, whereas the ionization energy has the value 0.25 eV. The variation of the Hall mobility as well as the carrier concentration with temperature was investigated. The scattering mechanism of the carrier in the whole temperature range of investigation was checked.

Vibrational Spectra of TlGaTe2, TlInTe2, and TlInSe2 Layer Single Crystals

AbstractPolarized IR‐reflection and Raman scattering spectra are obtained for TlGaTe2, TlInTe2, and TlInSe2 crystals (space group D). The IR‐reflection spectra of all the crystals show the presence of two (E ‖ c) and three (E ⟂ c) modes, which is in full agreement with the prediction of a group‐theoretical analysis. All seven Raman active modes are detected in TlInSe2. In TlGaTe2 and in TlInTe2 only three of seven Raman active modes can be observed. Normal coordinates, effective force constants, and effective charges are determined for the infra‐red active lattice vibrations.