SPECTRAL-ANALYSIS OF ABOVE-EDGE, BELOW-EDGE, AND NEAR-BAND-EDGE PHENOMENA IN GAN THIN-FILMS

We report spectroscopic ellipsometry (SE) and low-temperature reflecta nce data on epitaxial GaN thin film samples covering the widest range of tensile and compressive stress (-3.8-3.5 kbar) thus far. SE allows us to assess the preparation of smooth and abrupt GaN surfaces by chem ical treatments in real time, and, coupled with the reflectance data, the E dn/dE contribution to dispersion, which is important for laser a ction. The reflectance data explicitly show the nonlinear behavior of the B-A and C-A splittings versus the energy of the A exciton. Linesha pe ambiguities that hindered previous interpretations have been resolv ed with reciprocal space analysis, allowing us to obtain band paramete rs such as Delta(SO) = 17.0 +/- 1 meV and Delta(CF) = 9.8 +/- 1 meV wi th increased confidence. (C) 1997 Elsevier Science S.A.