Photoelectrochemical Properties of InGaN Thin Film Grown By Plasma Assisted Molecular Beam Epitaxy

In this work, high quality epitaxial In_xGa_(1-x)N films were synthesized on Si (111) substrate using plasma assisted molecular beam epitaxy (PAMBE) and applied for photoelectrochemical (PEC) application. The study demonstrated that a proper tuning of composition via controlling the In/Ga ratio the PEC performance of InGaN can be optimized. X-ray diffraction study confirmed the controllable formation of c-axis In_xGa_(1-x)N with different compositions. Photoluminescence results indicated the variation of band gap energy within 2.4~2.8 eV depending on In/Ga ratio. Transmission electron microscopic study confirmed the epitaxial growth of InGaN films, without observable evidence of phase separation at ~0.88% lattice mismatch between InGaN and Si substrate. From the PEC study, performed in hydrochloric acid solution (1M), an optimum efficiency of 1.31% was achieved with 15.5% In content in the InGaN. Detailed electrochemical and optical studies were carried out to address the factors that might influence the PEC performance, such as the crystallinity, carrier concentration, band gap energy, energy level position, and protons diffusion length. We believe that this study could lead to a better insight into the issue of InGaN for PEC application.

Keywords: plasma assisted molecular beam epitaxy, InGaN, water splitting, carrier concentration