F. Budde

Stabilization of amorphous GaN by oxygen

We have investigated experimentally the structure of disordered GaN films. The results suggest that it is not possible to stabilize an amorphous network in stoichiometric films, and the GaN instead consists of random-stacked nanocrystals of some 3-nm diameter. However, incorporation of 15% or more oxygen stabilizes an amorphous phase, which we attribute to the presence of nontetrahedral bonds centered on oxygen. The ionic favorability of heteropolar bonds and its strikingly simple constraint to even-membered rings are the likely causes of the instability of stoichiometric a-GaN.

Filled and empty states of disordered GaN studied by x-ray absorption and emission

X-ray absorption and emission spectroscopies are used to study the effects of short-ranged ordering on the electronic states of disordered GaN. Nanocrystalline samples with crystallites as small as 3nm exhibit an electronic structure resembling a broadened version of that in crystalline GaN. The electronic structure is even more heavily broadened in amorphous GaN films containing oxygen impurities or excess gallium. The oxygen containing films show an additional peak in the density of states just above the conduction band edge, and a downward shift of the valence band edge. The signature of molecular nitrogen trapped within the films is evident in both the absorption and emission spectra.

Electronic properties of (Ga,Mn)N thin films with high Mn content

The authors gratefully acknowledge financial support from the New Zealand Foundation for Research Science and Technology through its New Economy Research Fund and through a postdoctoral fellowship of one of the authors B.J.R.. The work of the MacDiarmid Institute is supported by a New Zealand Centre of Research Excellence award. Another author S.G. wishes to thank Education New Zealand for financial support of the XANES measurements.

Nanostructured amorphous group III nitrides: potential for refractive index engineering

Amorphous and nanocrystalline group III nitrides can be formed with relative ease in comparison with fully single crystalline material, and they show at least some properties in common with the crystalline form. Here we report experiments with the preparation of these materials, focussing especially on the potential to form patterned films with structures whose dimensions are comparable to visible wavelengths. There are clear opportunities to form both self-assembled and controlled patterns.