PHOTOTHERMAL DEFLECTION ANALYSIS OF β-In2S3 THIN FILMS: THE EFFECT OF S/In MOLAR RATIOS

Abstract

$\beta$-In₂S₃ thin films ($\mathrm{\text{S/In}}=1$, 2 and 4) were prepared using the pneumatic spray pyrolysis (PSP) route to analyze the effect of the S/In ratio on the physical properties. These properties were conducted using the photothermal deflection spectroscopy (PDS) method. The PDS signal amplitudes as a function of wavelength show multiple reflections which appear for all prepared In₂S₃ films. Such multiple reflections indicate homogeneity and high crystalline quality of the films. The deduced values of the optical band gap vary in the range 2.55–2.65$$eV. The highest thermal diffusivity is obtained for $\mathrm{\text{S/In}}=2$. The product ($\mu \cdot \tau$) is found in order of 10${}^{-8}$$$cm${}^{-1}$/V. The estimated carrier diffusion lengths are 0.06, 0.11 and 0.09$$$\mu$m for films corresponding to $\mathrm{\text{S/In}}=1$, 2 and 4, respectively. Defect absorption in $\beta$-In₂S₃ films is also investigated by PDS. Five absorption peaks are observed. These absorption peaks contain defect information in the band gap. Hence, this work evidences that $\beta$-In₂S₃ is a multi-functional material that can be used in optoelectronic, photovoltaic and visible-irradiation photocatalyst applications.