Structure formation and mechanisms of DC conduction in thermally evaporated nanocrystallite structure ZnIn2Se4 thin films

ZnIn2Se4 is of polycrystalline structure in as synthesized condition. It transforms to nanocrystallite structure of ZnIn2Se4 film upon thermal evaporation. Annealing temperatures influenced crystallite size, dislocation density and internal strain. The hot probe test showed that ZnIn2Se4 thin films are n-type semiconductor. The dark electrical resistivity versus reciprocal temperature for planar structure of Au/ZnIn2Se4/Au showed existence of two operating conduction mechanisms depending on temperature. At temperatures >365 K, intrinsic conduction operates with activation energy of 0.837 eV. At temperatures <365 K, extrinsic conduction takes place with activation energy of 0.18 eV. The operating conduction mechanism in extrinsic region is variable range hopping. The parameters such as density of states at Fermi level, hopping distance and average hopping energy have been determined and it was found that they depend on film thickness. The dark current–voltage characteristics of Au/n-ZnIn2Se4/p-Si/Al diode at different temperatures ranging from 293–353 K have been investigated. Results showed rectification behavior. At forward bias potential <0.2 V, thermionic emission of electrons from ZnIn2Se4 film over a potential barrier of 0.28 V takes place. At forward bias potential >0.2 V, single trap space charge limited current is operating. The trap concentration and trap energy level have been determined as 3.12×1019 cm−3 and 0.24 eV, respectively.