Growth and characterization of Cu2ZnGeSe4 thin films by selenization of multiple stacks (Cu/Se/ZnSe/Se/Ge/Se) in high vacuum

• CZGSe thin films are prepared by selenization of multiple stacks using novel precursors (Cu/Se/ZnSe/Se/Ge/Se) x 4.
• Effect of selenization temperature on the composition, structure, morphology, optical and electrical properties of CZGSe thin films was studied.
• SIMS depth profile confirms the nominal distribution of constituent elements in CZGSe films.
• XRD and Raman analysis confirmed the existence of minor ZnSe phase along with CZGSe phase.
• The films selenized at 450 °C showing perfectly packed rice shaped cylindrical grains.

Multiple stacks of precursors (Cu/Se/ZnSe/Se/Ge/Se) are deposited by electron beam evaporation followed by selenization in high vacuum at substrate temperatures ranging from 350 °C – 500 °C for 30 min to achieve device quality Cu2ZnGeSe4 films. The effect of selenization temperature on the structural, morphological, compositional, optical and electrical properties of Cu2ZnGeSe4 films are studied and discussed systematically. The crystal structure of Cu2ZnGeSe4 thin films selenized at 450 °C is found to be tetragonal stannite with lattice parameters a = 5.592(1) Å and c = 11.057(5) Å. The energy dispersive spectroscopic studies revealed the presence of Cu-poor and Zn-rich Cu2ZnGeSe4 films. The secondary ion mass spectroscopic (SIMS) analysis has been carried out to know the distribution of constituent elements across the thickness and found to be fairly uniform. The micrographs of Cu2ZnGeSe4 films selenized at 450 °C showing perfectly packed rice shaped cylindrical grains. Raman spectra revealed the existence of a minor ZnSe binary phase along with Cu2ZnGeSe4 phase. The optical energy band gap of Cu2ZnGeSe4 films was found to be 1.6 eV and these films have p-type conductivity with electrical resistivity of 2.13 × 10−3 Ωcm.