Microphotoluminescence spectra of hillocks in Al0.11Ga0.89N films

The spatial variation of the optical properties of hillocks in Al0.11Ga0.89N films has been studied by using microphotoluminescence (μ-PL) microscopy. The μ-PL spectrum revealed a strong emission (IH) at 351nm from the hillock, besides the near-band-edge emission (Inbe) at 341nm. Moreover, the IH intensity increases significantly and its full width at half maximum decreases from ∼76to∼53meV by probing across the hillock center. These indicated that the hillock structure is a strong emission center. The temperature-dependent μ-PL measurements showed that the IH also has the S-shape behavior with a transition temperature of ∼120K which is lower than that of Inbe. The redshift of IH is also smaller than Inbe. Both indicated that the Al composition in hillocks is lower than the surrounding area.