Injection currents in narrow-gap (Pb1−x SnxTe):In insulators

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

“…Although the occurrence of a "metal-dielectric transition" in PbSnTe:In at temperatures 20 TK ≤ presents a widely recognized fact, manifested as Fermilevel pinning at the middle of the energy gap of PbSnTe:In and resulting in a low (almost intrinsic) concentration of charge carriers in the material, available literature tacitly assumes that in dielectric state no contact injection occurs in PbSnTe samples, and only equilibrium charge carriers define the charge transport in the material. Yet, it was firmly established in (Akimov et al, 2005) that at helium temperatures in electric fields stronger than about 100 V/cm PbSnTe:In samples become dominated by space-charge-limited injection currents in the presence of electron traps, with the temperature dependence of the current showing a good agreement with calculations performed by the theory of space-charge-limited currents on the assumption of temperature-dependent static dielectric permittivity of the material. It was found that the behavior of static dielectric permittivity as a function of temperature depends on the strength of an electric field superimposed onto the sample, this fact complicating the description of the current versus voltage and temperature (Klimov & Shumsky, 2003).…”

“…In our experiments, measurements were carried out under conditions with background radiation screening, so that the feedback was ensured by some other mechanism. Previously, we showed (Akimov et al, 2005) that electron transport in semi-insulating PbSnTe:In at helium temperatures cannot be treated without regard for monopolar injection of electrons out of contacts and space-charge-controlled limitation of the current with capture of electrons into localized centers in the forbidden band of PbSnTe. Such an approach has allowed us to explain the shape of current-voltage curves, the high photosensitivity of PbSnTe in the fundamental absorption band, and the emergence of photosignal during excitation of the material in submillimeter band; additionally, an analysis of current-voltage characteristics has allowed us to determine the energy spectrum of localized electron traps ).…”

“…The temperature dependence of both, Auger and radiative, lifetimes at various contact injection levels is shown in Figure 13 a. At helium temperatures, the chosen minimal total concentration of equilibrium and field-injected electrons refers to the case of almost empty traps, while the maximal total concentration of electrons, to almost completely filled traps (Akimov et al, 2005). Measurements showed that our PbSnTe:In films were dominated by radiative recombination.…”

“…In «dielectric state», discussed in Introduction, at low concentrations of charge carriers in the allowed bands transport of charge carriers should obey the theory of space-charge-limited currents (Akimov et al, 2005). With traps for charge carriers present in PbSnTe:In, the filling of such traps should have an influence both on the current-voltage characteristics and on the photoconduction relaxation.…”

Far infrared and submillimeter range photosensitive devices based on Pb 1-x Sn x Te<In> films: results and perspectives

“…For LTT<In> it is commonly assumed in the literature that the charge carrier's transport is only determined by the equilibrium electrons and holes, as for ordinary semiconductors. However, it was shown 12) that the current voltage characteristics (CVC) of the LTT<In> films can be described only in the context of the SCLC-theory and injection of electrons from the contacts. Additionaly, it was shown 6,19) that the low-frequency permittivity (ε) is strongly depends on the temperature, electrical field and illumination.…”