Growth by molecular beam epitaxy of amorphous and crystalline GaNAs alloys with band gaps from 3.4 to 0.8 eV for solar energy conversion devices

Using low temperature MBE, we have shown that it is possible to grow amorphous GaN1-xAsx layers with a variable As content (0 < x < 0.8) on both crystalline (sapphire and silicon) and amorphous (glass and Pyrex glass) substrates. Despite the fact that the samples with high As content are amorphous, we observe a gradual continuous decrease of bandgap from similar to 3.4 to similar to 0.8 eV with increase in As content. To the best of our knowledge this is the first demonstration of homogeneous amorphous GaN-based alloys over a wide composition range. The large band gap range of the amorphous phase of GaNAs covers much of the solar spectrum. The amorphous nature of the GaNAs alloys is particularly advantageous since low cost substrates such as glass and Pyrex glass can be used for solar cell fabrication.