Structural and optical properties of Si-doped Al0.08In0.08Ga0.84N thin films grown on different substrates for optoelectronic devices

• Quaternary n-Al0.08In0.08Ga0.84N thin films were grown epitaxially on sapphire and p-Si substrates.
• High structural qualities without defects, small FWHM, low dislocation density, small RMS and smooth morphologies.
• The compressive strain of both samples was obtained.
• A red shift of the quaternary n-Al0.08In0.08Ga0.84N thin film grown on the p-Si substrate of band gap energy.

The objective of the current study is to characterize the optoelectronic properties of quaternary n-Al0.08In0.08Ga0.84N thin films grown via molecular beam epitaxy (MBE) on sapphire (Al2O3) and silicon (Si) substrates for different optoelectronic applications. Due to mismatch problems between the epilayer and substrates, the AlN buffer layer was inserted at low temperature to reduce the lattice mismatch to approximately 4% for the samples, to produce high-quality epitaxy films. Defect-free films with high structural, optical and electrical qualities were obtained. Their small full width at half maximum, low compressive strain, relatively large grain size and low dislocation density which produced smooth surfaces without any separation phases or cracks were characterized using X-ray diffraction analysis. Scanning electron microscopy, energy-dispersive X-ray microscopy and atomic force microscopy images confirmed these characterizations. Furthermore, high optical quality, as well as high absorption and absorption coefficients were observed using photoluminescence and UV-VIS spectroscopy; however, a red shift was observed in the PL peak of the near band edge of 3.158 eV of the sample on Si substrate compared with 3.37 eV for the sample on sapphire substrate which is attributed to the compressive strain and occurrence of the quantum confined Stark effect.