LUMINESCENCE AND ABSORPTION OF GAN FILMS UNDER HIGH-EXCITATION

The samples studied are thin GaN epilayers grown by metalorganic vapor phase epitaxy (MOVPE). At liquid helium temperature, the linear lumin escence, transmission and reflection spectra of the films has been rec orded, as well as the nonlinear emission spectra under high UV excitat ion, By using the variable strip length method, we have measured the g ain coefficient as a function of the excitation intensity and the temp erature. Pump and probe experiments have been performed in the femtose cond regime, showing crossed two-photon absorption without long lastin g response. This allows to envisage the use of GaN for the characteriz ation femtosecond pulses in the blue spectral range. (C) 1997 Elsevier Science S.A.