Nitrogen-hydrogen complex in GaAsxN1-x revealed by x-ray absorption spectroscopy

GaAsN alloys belong to a class of semiconductors with fascinating physical properties. Indeed, a small amount of nitrogen incorporation in GaAs leads to a counterintuitive and large band-gap reduction, and to an unexpected sudden increase in the effective mass of electrons. Even more surprisingly, both electronic and structural changes can be reversed fully and in a tunable manner by hydrogen incorporation. In this paper, we combine x-ray absorption spectroscopy at the nitrogen edge with ab initio simulations to investigate the atomic geometry of N-H complexes in hydrogenated GaAsN. In this way, we provide experimental evidence that dihydrogen-nitrogen complexes with C2v symmetry are the most abundant species in hydrogenated GaAsN. This finding contradicts previous predictions of "in-line" N-H2* complexes as the predominant species, and accounts for recent infrared absorption experiments.