Growth by Molecular Beam Epitaxy of GaNAs Alloys with High As Content for Potential Photoanode Applications in Hydrogen Production

We have studied the low-temperature growth of GaNAs layers on sapphire substrates by plasma-assisted molecular beam epitaxy. We have succeeded in achieving GaN 1-x As x alloys over a large composition range by growing the films at temperature much below the normal GaN growth temperatures with increasing the As 2 flux as well as Ga:N flux ratio. We found that the alloys with high As content x>0.1 are amorphous. Optical absorption measurements reveal a continuous gradual decrease of band gap from ˜3.4 eV to ˜1.4 eV with increasing As content. The energy gap reaches its minimum of ˜1.4 eV at the x˜0.6-0.7. For amorphous GaAsN alloys with x 1-x As x alloys have short-range ordering that resembles random crystalline GaN 1-x As x alloys. Such amorphous GaN 1-x As x alloys with tunable electronic structure may be useful as photoanodes in photo-electrochemical cells for hydrogen production.