Hydrogen in group III nitrides, studied by muon spin resonance

Abstract

This paper reviews recent work on the properties of hydrogen defect centres in two group III nitrides, AlN and GaN,and relevant studies by µSR spectroscopy, i.e. muon spin rotation,relaxation and resonance. We highlight, especially, results obtained by a form of nuclear quadrupole resonance. Implanted positive muons are used to mimic and model the behaviourof interstitial protons. The resultant defect centres exhibit bothmetastability and bistability. In AlN, they remain as positive ions butpartition themselves between a highly mobile species and one that is trappedand immobilized to temperatures as high as 800 K in cage-like sites adjacent to nitrogen. The barrier to escape from the cage is 0.86 eV.In n-type GaN, the cage-site positive ions are stable only up to 200 K;above this temperature they capture electrons to convert to negatively chargedcentres, analogues of hydride ions, relocating to sites antibonding to gallium.These latter escape from the cage sites around 600 K with an activation energyof 1.5 eV to join more mobile negative ions diffusing via channel sites withan activation energy of 0.65 eV. Data on the neutral paramagnetic centre suggest thathydrogen can act as a shallow-donor in at least one other member of this family of materials, namely InN.