I.I. Ivanchik

Performance and spectral response of Pb1−xSnxTe(In) far-infrared photodetectors

We have compared directly the performance of a Pb1−xSnxTe(In) photodetector with that of two other state-of-the-art far-infrared detectors: a Si(Sb) blocked impurity band (BIB) detector and a Ge(Ga) photoconductor in an integrating cavity. The Pb1−xSnxTe(In) photodetector has current responsivity SI several orders of magnitude higher than the Si(Sb) BIB at wavelength λ=14.5 μm. Persistent photoresponse with SI∼103 A/W at 40 mV bias and 1 s integration time at the wavelengths λ=90 and 116 μm has also been observed in the Pb1−xSnxTe(In) photodetector. This is larger by a factor of ∼100 than the responsivity of the Ge(Ga) photoconductor in the same conditions.

Far infrared high-performance lead telluride-based photodetectors for space-born applications

Abstract A new class of far-infrared photodetectors based on lead-tin tellurides doped with group III impurities is presented. The persistent photoconductivity effect appearing in these materials provides an internal signal integration resulting in a considerable increase in signal-to-noise ratio. The techniques of the photomemory quenching are discussed. In some quenching regimes the effect of giant quantum efficiency stimulation has been observed. The possibility of the generation of photoinduced spatially non-equilibrium states provides the physical evidence for the construction of an integrating “continuous” focal-plane array based on Pb 1− x Sn x Te(In).

Raman spectroscopy of impurity states in gallium-doped PbTe

We present Raman spectra and results of galvanomagnetic measurements of PbTe single crystals, doped with gallium, between 10 and 300 K. The effect of persistent photoconductivity depends on the gallium concentration. In all samples well-resolved peaks were observed at about 104 cm-1 (impurity-induced PbTe LO mode) and 166 cm-1 at all temperatures. Another mode appears at about 117 cm-1 at temperature below 250 K. One additional mode, at about 188 cm-1, is observed in PbTe + 0.4 at% Ga. These modes are discussed in terms of local vibrations of impurities corresponding to different Ga charge states.

Far-infrared study of impurity local modes in gallium-doped PbTe

Abstract We present far-infrared reflection spectra and results of galvanomagnetic measurements of PbTe single crystals doped with gallium between 10 and 300 K. The analysis of the far-infrared reflection spectra was made by a fitting procedure based on the model of coupled oscillators. Together with the strong plasmon–phonon coupling we obtain three local modes of gallium at about 122, 166 and 192 cm −1 . The position of these modes depends of impurity center charge, and their intensity depends of temperature and of gallium concentration. Persistent photoconductivity effect was registered in the sample with 0.4 at.% Ga by galvanomagnetic and far-infrared measurements.

Structure of DX-like centers in narrow-band IV–VI semiconductors doped with group-III elements

This paper presents a study of the structure of the IR reflectance spectra in the sub-gap region of lead telluride doped with indium and gallium and the Raman spectra in PbTe(In). In the Raman and reflectance spectra of PbTe(In), features are observed at a frequency of ω0⋍120 cm−1, whose amplitude sharply increases at temperatures T below the temperature where delayed photoconductivity appears, Tc⋍25 K. A similar feature at a frequency of ω0⋍155 cm−1 is also observed in PbTe(Ga), with the amplitude of the feature sharply increasing for T>Tc⋍80 K. An analysis of the resulting data makes it possible to conclude that, in contrast with classical DX centers in III–V semiconductors, the microscopic structure of the impurity centers in the two-electron (DX-like) ground state does not correspond to an impurity atom shifted from a lattice site, whereas the impurity atom is shifted from a lattice site for the metastable one-electron impurity state.

Model of DX-like impurity centers in PbTe(Ga)

A new model is proposed for DX-like impurity centers, which are responsible for the Fermi-level stabilization and long-term relaxation effects in IV-VI semiconductors doped with group III elements. The model is based on the idea of a variable valence of the impurity, whereas the nature of the long-term effects at low temperatures is associated with the formation of an effective barrier caused by a change of two units in the impurity valence upon photoexcitation. The model is applied to an analysis of the photoconductivity spectra in PbTe(Ga). The model can also be applied to the classical DX centers in III-V semiconductors.

Photoconductivity of lead telluride-based doped alloys in the submillimeter wavelength range

Persistent photoconductivity in a Pb0.75Sn0.25Te(In) alloy initiated by monochromatic submillimeter-range radiation at wavelengths of 176 and 241 µm was observed at helium temperatures. This photoconductivity is shown to be associated with optical excitation of metastable impurity states.

Selective photoconductivity induced in PbTe(Ga) by a local phonon mode

Selective photoconductivity at frequency ω=155 cm− was discovered in PbTe(Ga) narrow-gap semiconductors at liquid-nitrogen temperatures. The corresponding energy is much lower than all characteristic energies of the electronic spectrum of the semiconductor. The effect is attributed to optical excitation of a local vibrational mode of an impurity center leading to delocalization of the electrons.

Instability of DX-like impurity centers in PbTe : Ga at annealing

The kinetics of variation in the resistance of PbTe:Ga single crystals, with their Fermi level pinned within the band gap, during annealing at temperatures of up to 400°C was studied for the first time. It is shown that annealing the crystals for only several minutes at 200–250°C leads to the transformation of the material, which is semi-insulating at low temperatures, into a strongly degenerate semiconductor with a free electron concentration of about 10−18 cm−3. In other words, annealing results in the decomposition of DX-like impurity centers, which account for Fermi level pinning within the PbTe:Ga band gap. The corresponding activation energy is determined. It is found that high-temperature annealing at about 400°C promotes the tendency to a partial recovery of semi-insulating properties.

Magnetic-field-induced localization in Pb1-xSnxTe(In)

The authors report on the high-field (H<400 kOe) magnetoresistance of initially dielectric Pb0.75Sn0.25Te(In). The data taken at 1.4-4.2 K show an increase in magnetoresistance with time (localization) for a relatively low concentration of nonequilibrium electrons n. The characteristic time for localization tau depends exponentially on H and linearly on T. The possible origins of the effect are discussed.