Impact of annealing on the growth dynamics of indium sulphide buffer layers

Abstract

Thin films of Indium sulphide are deposited on corning glass substrate by thermal evaporation at room temperature (300 K). The as-deposited films were annealed from 373 to 723 K under vacuum ∼1 × 10−3 mbar. An amorphous phase is obtained from 300 to 473 K; the polycrystalline β-In2S3 emerges at 523 K, and In2O3 is grown at 723 K. The intermediary phases of β-In2S3 and In2O3 are perceived from 573 to 673 K. A clear distinction between the morphology of β-In2S3 and In2O3 was observed in the micrographs of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The β-In2S3 dominated films provide absorption coefficient (α) from 18 to 25 × 104 cm−1, while α values of In2O3 layers lie within 1–5 × 104 cm−1. The bandgap (Eg) of β-In2S3 thin films is low (2.34 eV), and that of In2O3 is high (3.47 eV); however, the intermediary phases of β-In2S3 and In2O3 exhibit bandgap tunning from 2.30 to 3.14 eV. Moreover, the β-In2S3 shows the highest carrier concentration (Nd; 3.25 × 1018 cm−3), In2O3 provides the highest mobility (μ; 228 Cm2/V.s), and intermediary phases exhibit the lowest resistivity (ρ; 1.27 × 103 Ω/cm) within the existing forms. The thin films β-In2S3 phase grown at 523 and 573 K meet its stoichiometric ratio. In comparison, the In2O3 phase emerges under high oxygen and sulphur deficit conditions. The films are suitable for photo-conduction devices and in the buffer/window layer of PV solar cell design.

Keywords

• Thin films
• β-In2S3
• In2O3
• Thermal annealing
• Crystallites
• Bandgap