Abstract
Among the photochemical reaction materials, TiO2 is a superior photocatalyst for water splitting to generate hydrogen because it has a suitable gap and is less toxic, easy to obtain, and resistant to either photoanodic or photocathodic corrosion. Unfortunately, high electron-hole recombination rate, low quantum efficiency, and low response to visible light limit its efficiency for hydrogen production. In this study, GaAs array was chosen as the main absorber for visible light to enhance the photoinduced water splitting. Intrinsic GaAs array was firstly fabricated by molecular beam epitaxy (MBE) using Au as the catalyst on Si (111) substrate. The pressures of As and Ga gases were 2.5x10-6 torr and 1x10-7 torr, respectively. The diameter and length of GaAs wires were respectively about 50 nm and several micrometers when the substrate temperature was set at 550 oC, as shown in Fig 1. After growth of GaAs array, TiO2 was coated on the surface of GaAs array by atomic layer deposition (ALD) with the precursors of TiCl4 and H2O for the sources of Ti and O2, respectively. The growth rate of TiO2 at 100 oC was about 0.5 Å/cycle. As shown in Fig 2, it has a thickness of 20 nm with 400 cycles of ALD. The core-shell GaAs/TiO2 nanowire arrays were tested for the water splitting reaction.