Hydrogen-nitrogen tailors semiconductor optoelectronics: The case of dilute nitride III-V alloys

Hydrogen is an omnipresent impurity in semiconductors; often associated with other impurities and native defects; strongly affecting their electronic properties by passivating deep and shallow levels, or activating isoelectronic centers, and can be intentionally or unintentionally incorporated. On the other hand, nitrogen has profound effects on the electronic structure of conventional III-V compounds: just a few percent of N can drastically lower the band gap of GaAs making it suitable for long-wavelength optical devices; isovalent doping of GaP by N leads to a quasidirect band gap with enhanced optical functionality. The large difference in electronegativity between N and other group V elements is expected to couple with the high chemical activity of H, raising crucial questions about the behavior of H in dilute nitride alloys that theories of hydrogen in conventional semiconductors or in common-anion nitrides are unable to answer. Here we show that N can qualitatively alter the electronic behavior of hydrogen: In GaAsN, an H atom bonds to N and can act as a donor in its own right, whereas in GaAs and GaN, H is amphoteric; Nitrogen also stabilizes the H-2* complex, that is otherwise unstable against the formation of interstitial H-2 molecules; reversing the effect of N on the band gap of GaAS; allowing us to interpret several recent experiments.