The effect of atomic hydrogen irradiation during molecular beam epitaxy (MBE) on the electrical properties of GaInNAs thin films and the characteristics of homojunction GaInNAs solar cells are presented. We found that an optimum amount of atomic H flux irradiated during MBE growth of GaInNAs material is effective for suppressing or passivating the defects that act to mainly trap the electrons. Furthermore, an enhanced layer-by-layer growth improves the uniformity of GaInNAs layers thereby reducing the segregation and clustering of N atoms. A p-i-n Ga(0.984)In(0.016)N(x)As(1-x) solar cell fabricated by atomic H-assisted MBE shows a short-circuit current density of 22.2 mA/cm(2). (C) 2009 Elsevier B.V. All rights reserved.