Effect of Pre‐annealing Treatment on Growth and Properties of (Cu_0.5Ag_0.5)₂ZnSnSe₄ Thin Films

Abstract

In this work, the preparation of “Ag” alloying Cu2ZnSnSe4 films using a two‐step process, comprising vacuum evaporated ([Sn/ZnSe/Ag/Sn/ZnSe/Cu] × 2) precursor layer deposition on glass substrates followed by low‐temperature pre‐annealing treatment (PAT) in Se ambiance (200–400 °C) for 30 min and high‐temperature annealing at 500 °C for 1 min, is reported. The low‐temperature PAT provides adequate Se diffusion into precursor layers and plays a pivotal influence on the growth and properties of (Cu,Ag)2ZnSnSe4 films. The Zn/Sn and Se/metals ratios are found to be varied in the range 0.77–1.32 and 1.07–0.86 with PAT (200–400 °C) followed by annealing at 500 °C for 1 min. The precursor layers are pre‐annealed at 300 °C for 30 min, followed by annealing at 500 °C for 1 min, found to be nearly stoichiometric with uniform distribution of constituents. The valence states of the constituents are confirmed by X‐Ray photoelectron spectroscopy. Both X‐Ray diffraction and Raman studies confirm the formation of single‐phase (Cu,Ag)2ZnSnSe4 along (112) orientation with a strong Raman mode at 194 cm−1. Large and well‐defined grains with a mean size of 0.7 μm are seen in the field‐emission scanning electron microscope images. The (Cu,Ag)2ZnSnSe4 films exhibit a direct bandgap of 1.12 eV and p‐type conductivity with high mobility, 5.23 cm2 V−1 s−1.