Are AlN and GaN substrates useful for the growth of non-polar nitride films for UV emission? The oscillator strength perspective

The authors present results of a perturbation theory study of the effect of strain on the oscillator strengths of interband transitions in wurtzite group-III-nitride films suitable for ultraviolet light emission applications. Ternary alloy films are investigated, which can be pseudomorphically grown on GaN and AlN substrates with nonpolar M-plane (1 (1) over bar 00) and A-plane (11 (2) over bar0) orientations. Valence band mixing, induced by the anisotropic in-plane strain that arises in these films, can have a dramatic influence on the optical polarization properties of the transitions. An increased efficiency of light emission in the 0.21 mu m to 0.25 mu m spectral range is best achieved using AlN substrates, on which both Al1-xGaxN and Al1-xInxN films experience compressive strain. On GaN substrates, Al1-xGaxN films experience tensile strain and will exhibit poor light emission efficiency. However Al1-xInxN films on GaN substrates can emit light efficiently in the 0.3 mu m to 0.36 mu m spectral range. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim