Optical properties of GaN quantum dots

We report on an investigation of the optical properties of GaN quantum dots (QDs) grown by means of metalorganic vapor phase epitaxy. The growth regim e for GaN on AlxGa1-xN was observed to change from two- to three-dimensiona l, forming GaN QDs, when Si was deposited on the AlxGa1-xN surface prior to the GaN growth. These QDs showed a redshift of the photo luminescence (PL) energy from the increased Coulomb energy induced by a compression of the e xciton Bohr radius. Furthermore, a diminishing temperature-dependent shift of the PL energy with decreasing QD size caused by a reduction of the longi tudinal-optical phonon coupling was found. We also show that the size of th e QDs is a critical parameter for the optical nonlinearities. For large dot s, the dominant nonlinearity in the PL is the bandgap renormalization but w hen the size of the dots was reduced below the critical size of 10 nm thick and 30 nm diameter, the state-filling effect became dominant. (C) 2000 Ame rican Institute of Physics. [S0021-8979(00)04708-3].