Effect of deposition pressure on structural, optical and electrical properties of zinc selenide thin films

ZnSe thin films have been prepared by inert gas condensation method at different gas pressures. The influence of deposition pressure, on structural, optical and electrical properties of polycrystalline ZnSe films have been investigated using X-ray diffraction (XRD), optical transmission and conductivity measurements. The X-ray diffraction study reveals the sphalerite cubic structure of the ZnSe films oriented along the (1 1 1) direction. The structural parameters such as particle size 6.65-22.24 nm], strain 4.01-46.6×10⁻³ lin⁻² m⁻⁴] and dislocation density 4.762-18.57×10¹⁵ lin m⁻²] have been evaluated. Optical transmittance measurements indicate the existence of direct allowed optical transition with a corresponding energy gap in the range 2.60-3.00 eV. The dark conductivity (σ_d) and photoconductivity (σ_ph) measurements, in the temperature range 253-358 K, indicate that the conduction in these materials is through an activated process having two activation energies. σ_d and σ_ph values decrease with the decrease in the crystallite size. The values of carrier life time have been calculated and are found to decrease with the reduction in the particle size. The conduction mechanism in present samples has been explained, and the density of surface states 9.84-21.4×10¹³ cm⁻²] and impurity concentration 4.66-31.80×10¹⁹ cm⁻³] have also been calculated.