Energy Spectra of the Local States in the Forbidden Gap of Monoclinic TlInS _2x Se _2(1−x) Crystals

Abstract

Near IR properties of the mixed TlInS_2xSe_2(1−x) have been studied previously by the present authors. In this work the temperature and frequency dependence's of the conductivity and the current-voltage characteristics (in relatively weak electric field), have been investigated for monoclinic TlInS_2xSe_2(1−x) crystals, which are perspective materials for IR applications. From the temperature dependence's of conductivity in the direction perpendicular to c- axis the band gap E^g = 2.22 eV was determined for β--TlInS₂ crystals. The impurity centres were determined located at 0.43, 0.73 eV and 0.35, 0.48, 1.12 eV for the direction of current i//c and i ⊥ c, respectively. The concentration of the centres located at 0.48 and 1.12 eV were calculated to be N_A − N_D = 4.8 · 10⁹ cm⁻³ and 1.9 · 10¹¹ cm⁻³, respectively. It was found that in the solid solutions TlInS_2xSe_2(1−x) for 0.3 ≤ x ≤ 1, the conductivity follows the dependence σ (v) = σ₀·υ^s in the temperature range between 100 to 600 K. In the temperature range of 80-400 K charge bounce plays an important role in the conductivity mechanism. Occurrence of the deep and low-levels impurity centres and a “tail” of the density of energy states in TlInS_2xSe_2(1−x) crystals make them perspective for practical applications: switching and memory effects, N-type current-voltage characteristics, induced conductivity etc.