AlxGa1-xN/GaN band offsets determined by deep-level emission

We present studies of the compositional dependence of the optical propertie s of AlxGa1-xN(0 <x <0.22) alloys by modulation spectroscopy and photolumin escence. The yellow luminescence, which is well known in GaN and is general ly assigned to shallow donor-deep acceptor pair recombination has also been observed in AlxGa1-xN. As aluminum concentration increases, the color of t he band changes from yellow (2.2 eV) to blue (2.6 eV). The shift was less t han that of the band gap. Together with previously published studies, it im plies that the deep acceptor level is pinned to a common reference level to both materials, thus the deep level responsible for the yellow emission is used as a common reference level to determine the band alignment in AlxGa1 -xN/GaN heterojunctions. Combining with the near-band-edge modulation spect ra, the estimated ratio of conduction-to-valence band discontinuity is 65:3 5. Our results are close to the values obtained from PL measurements on Al0 .14Ga0.86N/GaN quantum wells and those calculated by linear muffin-tin orbi tal method and linearized augmented plane wave method. (C) 2001 American In stitute of Physics.