Large exciton g-factors in anisotropically strained A-plane GaN film measured using magneto-optical Kerr effect spectroscopy

Abstract

Exciton Landé g-factors in wurtzite GaN epitaxial films with (0001) C-plane and (112¯0) A-plane orientations have been measured in magnetic fields B up to 1.8 T, using polar magneto-optical Kerr effect (MOKE) spectroscopy. A procedure is developed for extracting the Zeeman splitting and thereby the g-factor, from Kerr ellipticity and rotation spectra of A-plane films, which have in-plane polarization anisotropy. In the C-plane film the measured g-factors for the A, B, and C exciton transitions were gA=0.09±0.02, gB=0.74±0.05, and gC=3.9±0.2, respectively, with B∥c-axis and comparable to earlier reports. The MOKE spectra of the A-plane film have one dominant exciton feature each for analyzer axis ⊥ and ∥ to the c-axis of GaN, and they arise at different energies. The measured g-factors for these were much larger, with values g⊥c=4.7±1 and g||c=7.1±1.2 with B⊥c-axis. Comparison with a k·p perturbation theory based calculation, which included the influence of strain, indicates that the features in the A-plane film are associated with exciton transitions involving bands that are strongly mixed by the anisotropic in-plane strain.