Structural, optical, transient photoconductivity studies and low temperature thermoelectric power measurements on reactively evaporated lead selenide thin films

Abstract

Thin film of PbSe has been prepared on ultrasonically cleaned glass substrate at a substrate temperature of 373 ± 5 K by reactive evaporation at a pressure of 10⁻⁵ mbar. The prepared PbSe film is characterized using X-ray diffraction, scanning electron microscopy, and UV–Vis–NIR spectrophotometer. The average particle size, number of crystallite per unit area and strain of a typical film are calculated and found as 38 nm, 3.098 × 10¹⁵ m⁻² and 2.253 × 10⁻³ respectively. The room temperature electrical resistivity of the film is of the order of 0.16 Ω cm. The material possesses a direct allowed optical band gap of 2.02 eV and the absorption coefficient is found to be in the range 10⁴–10⁵ cm⁻¹. The weak absorption below the absorption band edge is observed and tailing in the forbidden gap is found to follow Urbach tail rule. The width of the localized states in the band gap is estimated as 256 meV. The differential life time increases with increasing decay time and the decay curve of the photocurrent gives the localized energy states which act as trapping centre in the band gap of the material. The thermoelectric power measurements are done in the temperature range 10–293 K and the Fermi level is positioned at 0.039 eV above the valence band. The material possesses a Seebeck coefficient of about 137 μV K⁻¹ and power factor of 0.12 × 10⁻⁴ Wm⁻¹ K⁻² near room temperature. The prepared films are of p-type in nature with activation energy of 0.063 eV.