O. MADKHALI: Structural, optical and electrical properties of copper and silver-copper iodide thin films

Abstract:
In this thesis, we study the formation of copper iodide (CuI) and silver copper iodide (Ag,Cu)I thin films from a two-step procedure: deposition of a metallic film by magnetron sputtering and iodination in iodine vapor. Numerous techniques have been used to determine the films properties such as: X-ray diffraction, transmission electron microscopy, Hall effect, UV-visible spectroscopy... For CuI films, we obtained transparent p-type semiconductors films crystallizing in the γ-phase with wide bandgap (Eg ≈ 3.05 eV). Copper iodide films grow with a strong preferred orientation along the [111] direction. SEM analysis of thin film morphology demonstrates that iodination conditions can affect crystal size. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) have revealed crystallographic twin domains in CuI crystals, revealing their geometry and orientation. The films are highly conductive, optically transparent and exhibit high value of figure of merit.
The properties of (Ag,Cu)I thin films have been studied using the same methods as a function of the silver content. (Ag,Cu)I films can be either p-type or n-type, depending on Ag concentration. Nevertheless, no structural change has been evidenced by XRD. The optical band gap can be monitor by the progressive addition of silver. The same is true for the electrical activation energy. In addition, the PL results showed a tendency of the PL spectral features of CuI to be changed to those of AgI with the increase of the silver content. A correlation between the optical and electrical results was established and evidenced the origin of the electrical behaviour. It is proposed that presence of Ag in (Ag,Cu)I thin films promotes the formation of the I-vacancies, which act as donor type defect, and eventually, with increasing the Ag content, crossover the carriers from p-type to n-type occurs.

Keywords:
Copper iodide, Silver copper iodide, Semiconductor, Sputtering, Optoelectronic applications.

Composition of the jury:
> Reporters:
- Antoine BARNABÉ, Professor, CIRIMAT, Toulouse
- Sandrine PERRUCHAS, Researcher - HDR, IMN, Nantes
> Examiners:
- Sidi OULD SAAD HAMADY, Professor, LMOPS, Metz
- Aline ROUGIER, Senior researcher, ICMCB, Bordeaux
> Thesis' direction:
- Jean-François PIERSON, Director of thesis, Professor, IJL, Nancy
- Maud JULLIEN, Co-director of thesis, Research engineer, IJL, Nancy