Tailoring the structural, electrical, optical and wettability properties of ZnSe films by oblique angle thermal evaporation

ZnSe films were prepared using thermal evaporation by keeping the substrates at angles of 0°, 60° and 75° with the horizontal direction. The film prepared at 0° had zinc-blende cubic crystal structure with an average crystallite size of 27 nm while the other two films showed very weak crystalline peaks due to the presence of a small amount of nano-crystallites. The Raman spectra of all the thin film samples show peaks at 256 cm⁻¹ due to the longitudinal optical (LO) mode that is blue shifted as compared to the LO peak at 245 cm⁻¹ in the commercial ZnSe powder sample. Globular structures protruding from the surface were observed in the FESEM and AFM images and the size of the globules decreased with an increase in the deposition angle. The root mean square surface roughness is 21 nm, 48 nm and 33 nm for films deposited at 0°, 60° and 75° respectively. The optical band gap is in the range: 2.71 to 2.75 eV and all the films were highly transparent in the mid-infrared region. The electrical conductivity increases with an increase in the deposition angle and the values are 4.84 × 10⁻⁹ ohm⁻¹ cm⁻¹, 9.51 × 10⁻⁹ ohm⁻¹ cm⁻¹ and 2.12 × 10⁻⁷ ohm⁻¹ cm⁻¹ (at 308 K) for the films deposited at 0°, 60° and 75° respectively. The water contact angle measurements found that the films grown at oblique angles have higher hydrophobicity as compared to the normally deposited film. The study elaborates the influence of oblique angle deposition in the modification of the structural, surface roughness, electrical, optical and wettability properties of ZnSe thin films. (paper)