GaNAs alloys over the whole composition range grown on crystalline and amorphous substrates

Using low temperature molecular beam epitaxy (LT-MBE) technique we have overcome the miscibility gap of GaAs and GaN alloys and successfully synthesized GaN_1-xAs_x alloys in the whole composition range on crystalline (sapphire and silicon) and amorphous (Pyrex glass) substrates. On the N-rich side we found an increased incorporation of As with decreasing growth temperature. At high enough As content the films lose their crystallinity and become amorphous. On sapphire substrate, the alloys are amorphous in the composition range of 0.17<x<0.75. For the films grown on glass substrates, the composition range for amorphous alloys extends to x∼0.1. However, films grown on silicon shows small fraction of As-rich and N-rich GaNAs nanocrystals for films with As content up to 36%. These amorphous GaNAs films have smooth morphology, homogeneous composition and sharp, well defined optical absorption edges. The bandgap energy of the GaN_1-xAs_x alloys covers a broad energy range from ~3.4 eV in GaN to~0.8 eV at x~0.85. This provides an almost perfect fit to the solar spectrum offering the opportunity to design high efficiency multijunction solar cells using a single ternary alloy system. The amorphous nature of this alloy over a wide alloy range can also be advantageous since they can be deposited on low-cost glass substrate. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.