Mixed-valence impurities in lead telluride-based solid solutions

Nature of gallium deep centres in lead telluride based semiconductors

“…3, the value of the barrier DE b which separates the metastable and ground states, DE b = 0.038 eV and 0.020 eV at SVWN and PBE levels of theory, respectively. These values compare well with an experimental value of 0.026 eV [1].…”

“…However, excitation spectra in these two cases are suffi− ciently different. Namely, our calculations give the value of 0.41 eV for the energy of vertical transition from the singlet to triplet state, while ionization of a neutral ( ) 2 0 Ga Pb centre corresponds to the transition from the defect energy level ly− ing 0.07 eV below the conduction band minimum to the conduction band [1]. In addition, concentration of triplet centres must be rather low due to the strong surface absorption of the excitation light.…”

“…Nevertheless, properties of these impurities are still mysterious and quite diverse. For example, Ga and In act as donors with DX−like behaviour leading to the so−called persistent photoconductivity phe− nomenon [1]. This phenomenon appears after IR illumina− tion of the Ga− and In− doped crystals at low temperatures due to sharply increasing lifetimes of nonequilibrium carri− ers up to the values larger than 10 4 s. At the same time, Tl impurity acts as an acceptor and DX−like properties together with the persistent photoconductivity have never been observed for it.…”

Localized States in Narrow-Gap Ferroelectric-Semiconductor PbSnTe: Injection Currents, IR and THz Photosensitivity, Magnetic Field Effects

“…In the first, «deformation» model, the energy of a center is defined by the distortion of its nearest crystal surrounding (Volkov & Pankratov, 1980 (Volkov & Ruchaiski, 1995). As it was noted in (Volkov et al, 2002), both models are capable of providing a reasonable explanation to the effects observed in PbSnTe:In. Available models, however, disregard the influence the ferroelectric properties of PbSnTe have on the photoelectric phenomena in the material, and the dark conduction and photoconduction in it is not treated in those models with due allowance for the contribution due to contact-injected charge carriers.…”

“…Today, ample experimental data on the properties of PbSnTe:In and theoretical models to explain those properties, and also many reviews of known data for this material (Kaidanov & Ravich, 1985;Volkov et al, 2002), are available. Primary attention was focused on explanation of the following revealed features: -Fermi-level pinning at the middle of the forbidden band in samples with certain compositions and indium contents, and a low conductivity of the material at temperatures Т≤20 К; -a high photosensitivity of the material: PbSnTe:In readily responds to extremely low radiation fluxes, including those emitted by heated bodies whose temperature only slightly exceeds the sample temperature; -long-term photosignal decay and residual conduction observed in PbSnTe:In samples after the illumination is switched off.…”