We report the growth of GdN thin films and a study of their structure and magnetic and conducting properties. It is demonstrated that they are semiconducting at ambient temperature with nitrogen vacancies the dominant dopant. The films are ferromagnetic below 68 K, and a significant narrowing of the band gap is signaled by more than a doubling of its conductivity. The conductivity in the low-temperature ferromagnetic state remains typical of a doped semiconductor, supporting the view that this material is semiconducting in its ground state and that no metal-insulator transition occurs at the Curie temperature.

We investigate the electronic band structure of two of the rare-earth nitrides, DyN and SmN. Resistivity measurements imply that both materials have a semiconducting ground state, and both show resistivity anomalies coinciding with the magnetic transition, despite the different magnetic states in DyN and SmN. X-ray absorption and emission measurements are in excellent agreement with densities of states obtained from LSDA+U calculations, although for SmN the calculations predict a zero band gap.

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We report the preparation of amorphous GaN by ion-assisted deposition and studies of the Raman and optical response of the resulting films. The films are transparent across the visible and show an edge whose energy and structure are in close agreement with crystalline material, suggesting a low density of gap states and homopolar bonds. The Raman spectrum is similar to a broadened vibrational density of modes calculated for wurtzite GaN, with a Raman cross section which varies among the vibrational bands.

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The structure of disordered GaN:O films grown by ion-assisted deposition is investigated using x-ray absorption near-edge spectroscopy and Raman spectroscopy. It is found that between 4 and 21% of the nitrogen in the films is in the form of molecular N 2 that interacts only weakly with the surrounding matrix. The anion to cation ratio in the GaN:O host remains close to unity, and there is a close correlation between the N 2 fraction, the level of oxygen impurities, and the absence of crystalline order in the GaN:O matrix.