Raman measurements on GaN thin films for PV - Purposes

Raman scattering (RS) is a very important experimental tool to characterize the optical modes and another elementary excitations of materials. Among other issues it can determine for example the degree of crystalline quality and point defects like local modes. Therefore GaN - thin films and related compounds for photovoltaic purposes and as processed by several systems have been measured by this technique. The films were grown by Molecular Beam Epitaxy (MBE), Close Spaced Vapor Transport (CSVT) and Laser Ablation (LA) with the use of optimal growth parameters and substrates. Gallium nitride crystallizes in the wurtzite structure with 4 atoms in the unit cell and presents 7 allowed Raman modes of A₁, E₁, and E₂ symmetries. In this work we present and discussed our Raman experiments where particularly the detection of the E₂ and A₁ modes are illustrated in these nitride semiconductor compounds.