The optical properties of Sb₂Se₃Sb₂Te₃

Abstract

The optical properties of single crystal specimens of Sb,Te,-Sb,Se, solid solutions have been investigated in the photon energy range 0.04 eV to 6.5 eV. A wide range of solid solutions having hexagonal structure were found to exhibit properties closely corresponding to the isostructural compounds Bi,Te, and Bi,Se,. Small indirect band gaps approaching semimetallic values were obtained. The high free-carrier concentrations gave rise to plasma effects in the near infra-red. I n contrast Sb,Se, is orthorhombic with a direct band gap near 1 eV. The chemical bonding concepts applied to similar systems seem applicable with only slight modification.Die optischen Eigenschaften von Sb,Te,-Sb,Se,-Mischkristallen wurden im Bereich von 0,04 eV bis 6,5 eV untersucht. Die Festkorperlosungen haben innerhalb weiter Grenzen die gleiche hexagonale Struktur wie die isostrukturellen Verbindungen Bi,Te, und Bi,Se, und zeigen sehr verwandte optische Eigenschaften. Kleine indirekte Energieschwellen Lhnlich denen in Halbleitern wurden beobachtet. Die grol3e Konzentration von freien Ladungstragern verursachte Plasmaerscheinungen im nahen Ultrarot. Sb,Se, ist orthorhombisch mit einem direkten verbotenen Energieband von 1 eV. Die chemischen Bindungskonzepte konnen wahrscheinlich mit nur geringen Veranderungen auf ahnliche Systeme angewendet werden.

Refinement of the Sb2Te3 and Sb2Te2Se structures and their relationship to nonstoichiometric Sb2Te3−y Se y compounds

“…Single crystals of SbzTe3_ySey were grown from the melt by a modified Bridgman technique (Procarione & Wood, 1970;Wood, Van Pelt & Hyland, 1972). The preparation of sufficiently small crystals for transmission techniques was unsatisfactory because of the resulting crystal deformation.…”

“…Their observation of a linear lattice constant change for 0 <y < 2 and of a phase separation of Sb2S% for compositions with y > 2 suggests that the Se may be substituted only into the Te a position. Procarione & Wood (1970) suspected this also on account of their optical data while phase-diagram and electronic measurements point to the reverse substitution mechanism (Ullner, 1968).…”

The electronic structure of the antimony chalcogenide series: Prospects for optoelectronic applications

“…Sb 2 S 3 has a direct optical band gap with experimental studies reporting a range from 1.66-2.24 eV [14,32,33,34,35,36,37,38,39,40,41], which is found to increase with the film thickness and temperature [42,43]. The nature of the band gap for Sb 2 Se 3 is also unclear but an experimental range of 1.00-1.82 eV has been reported, where the lower energy transitions are considered to be indirect [44,45,46,47]. A PBE study by Vadapoo et al [48] calculated an indirect band gap of 0.88 eV for Sb 2 Se 3 ; however this is likely to be an underestimated value which is often the case when using a GGA functional like PBE.…”

Point Defects in Sb2Te3−xSexCrystals

“…Increasing selenium content in the crystal lattice gives rise to variations in the physical properties of the mixed crystals, namely those of the transport coefficients and the optical properties in the infrared region; the reflectivity and transmittance of the crystals with various values of x were studied in Refs. (3,4); the transport coefficients and reflectivity in the plasma resonance region were studied also in our earlier papers (5,6). It follows unambiguously from these studies that gradual substitution of selenium atoms for tellurium in the crystal lattice of Sb Te gives rise to an increase in the Hall constant, to a drop of the electrical conductivity, and to a shift of the reflectivity minimum in the IR region toward longer wavelengths, which means that the concentration of holes decreases with increasing x.…”