Infrared reflection in the Reststrahlen region of GaN MBE grown epitaxial layers on Si substrates

Infrared reflectivity in the region of the Reststrahlen band has been inves tigated for molecular beam epitaxy (MBE) grown GaN epitaxial layers on Si s ubstrates with and without an AlN buffer layer. Deformation of the Reststra hlen band due to free carriers has been observed depending on whether the G aN layer was grown on an AIN buffer layer or directly on the Si substrate. A Lorentz oscillator for the phonon contribution and a Drude-Lorentz model for free carrier contribution to the complex dielectric function has been a ssumed in order to calculate and fit the reflectivity to the measured spect ra. Free carrier concentration and mobility has been evaluated from fitting parameters. The layers grown on AIN buffer layer have lower carrier concen tration and a by one order of magnitude higher carrier mobility than the la yer grown without AlN buffer layer. (C) 1999 Elsevier Science S.A. All righ ts reserved.