Influence of III–V substrates on the texture, structural, and optical properties of CdS thin films deposited by chemical bath deposition

We have studied the influence of texture distribution and crystalline structure of the CdS thin films on their optical properties. CdS samples were grown by chemical epitaxy on III–V substrates. Ga-V materials (c-GaAs and h-GaN) were selected due to the newly renovated interest in CdS/III–V heterostructures and their importance in the development of current optical devices, such as light emitter diodes and solar cells. Texture analysis was realized in pole diagrams obtained in a High-Resolution X-ray diffractometer. Measurements were carried out at 2θ = 26.6° and 2θ = 43.9° because these 2θ angles correspond to diffraction signal for cubic and hexagonal CdS phases, respectively. Pole diagrams show fourfold symmetry in the CdS layers deposited on GaAs (100) substrates and sixfold symmetry in CdS layers deposited on GaN (0002) substrates, which indicates that epitaxial CdS films with both crystal structures is possible by a low-cost technique (Chemical Bath Deposition). The structural study was completed with a surface analysis of the CdS samples by atomic force microscopy; the images obtained showed a greater surface roughness in the CdS layers grown on GaN substrates, this result agrees with the texture distribution observed in pole diagrams. Optical properties of radiative and non-radiative recombination were studied by Raman and photoluminescence (PL) spectroscopies. According to PL results, cubic CdS films have better efficiency in the recombination of radiative bands. In addition, we determined that the CdS–A₁LO phonon for the cubic monocrystalline phase is located at 302.35 cm⁻¹, which is 0.84 cm⁻¹ smaller than hexagonal structure.