Study of Growth Mechanism and Properties of Zinc Indium Sulfide Thin Films Deposited by Atomic Layer Chemical Vapor Deposition over the Entire Range of Composition

In this study, zinc indium sulfide (ZIS) thin films of different compositions ranging from pure In2S3 to pure ZnS were synthesized by atomic layer chemical vapor deposition (ALCVD). In situ growth mechanism studies were carried out using the quartz crystal microbalance technique. They evidence preferential surface exchange reactions between indium and zinc ions during ALCVD pulses, which control the overall composition. Optical characterizations indicate a bandgap varying from 2.0 eV with indirect transition for In2S3 to 3.6 eV with direct transition for ZnS. As deposited films present good crystallinity toward the two binary compounds which decreases at intermediate compositions. An amorphous phase appears in the material for the In/(In + Zn) ratio in the range 11–73 at % attributed to the conflict between the crystallographic structures of ZnS and In2S3. Under thermal annealing treatments, grown films undergo crystallization processes. In particular, the thermal annealing of a sample with In/(In + Zn) ∼ 73 at % leads to the formation of the crystalline phase ZnIn2S4 with the presence of the crystallized In2S3 phase.