Blue emission and twin structure of p-type copper iodide thin films

Abstract

Copper iodide is an attractive p-type transparent material suitable for optoelectronic applications. This work reports on the synthesis of copper iodide (CuI) by iodination of sputtered Cu films previously deposited on glass and silicon substrates. The crystalline phase and surface morphology were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The prepared CuI films crystallize in the zinc blende structure (γ-phase) at different amounts of iodine and exhibit preferential orientation along the <111> direction. Moreover, detailed investigation of the microstructure via high-resolution transmission electron microscopy (HR-TEM) revealed the presence and details of alternating twin crystallographic domains between adjacent grains. The electrical properties of the CuI films were characterized by Hall effect measurements and revealed a p-type carrier behavior for all films. The electrical behavior was discussed and attributed to the change in intrinsic point defects. In addition, the electronic bandgap and luminescence properties were investigated using optical transmission and photoluminescence (PL). The CuI films showed a wide band gap (about 3.05 eV) with an average transmittance of about (66 %) in the visible region. Moreover, the PL showed a blue emission ranging from 400 to 440 nm originating from the excitonic recombination and radiative point defects.