Impedance spectroscopy study of Al/p-Cu2ZnSnS4 thin films Schottky diode grown by a two-stage method
Résumé
This work highlights some physical properties of Al/p-Cu2ZnSnS4 Schottky diode grown by a
two-step method. Initially, Cu2ZnSnS4 (CZTS) ingots were successfully prepared by direct
melting of the constituent elements from high purity stoichiometric compositions. The CZTS
thin films were prepared by a single-source thermal vacuum evaporation method (10-5 Torr) on
molybdenum substrate heated to 100 °C. Subsequently, the deposited CZTS sample was
annealed in a Sulphur atmosphere at 400 °C for 30 min.
Structural and morphological analysis was performed by X-ray diffraction, Raman scattering
and scanning electron microscopy. Diffuse reflectance spectra were performed in order to
evaluate the optical properties of the powder. Electrical investigations of the CZTS powder and
the Al/p-Cu2ZnSnS4 junction were conducted by current-voltage (I-V) measurements and AC
impedance spectroscopy over a wide temperature range up to 653 K in the frequency range 5
Hz-13 MHz. The experimental X-ray diffraction data indicated that the CZTS powder exhibits
a kesterite structure. For bulk material, the band gap energy is about 1.39 eV, the complex
impedance plots display a semicircle with an equivalent circuit consisting of a parallel RC
circuit connected to a series resistor. For the CZTS thin film, X-ray diffraction revealed the
presence of the kesterite phase with some additional peaks such as Mo and MoS2 and the film
thickness was about 450 nm. The as-deposited CZTS films showed p-type conductivity
according to the hot probe method. Based on the I-V characteristics, the aluminum layer formed
a Schottky contact with the p-CZTS absorber layer. Characteristic parameters such as saturation current, ideality factor and series resistance were calculated from the experimental I-V data.
These parameters showed significant electrical properties such as low series resistance and an
ideality factor between 1 and 2. The complex impedance plots shows a semicircle with
equivalent circuit functions as a typical parallel RC. We also noted a decrease in total parallel
resistance Rp and capacitance Cp with temperature. Finally, the Arrhenius diagram provided a
very low activation energy of about 2.03 meV.