ABSTRACT
The thickness of ultra-thin AlN layers, which are used as intermediate layers between heteroepitaxial GaN/Sapphire, has been determined by the Fresnel contrast method (FCM) in high resolution transmission electron microscopy (HRTEM) images. The thickness measured by FCM has been adjusted from simulated HRTEM images, which have been generated controlling the number of atoms in the AlN intermediate layer. The critical thickness of the AlN-IL has been calculated using theoretical calculations based on thermodynamic equilibrium. Several series of samples had been grown varying the number of AlN-ILs and the distance of separation among AlN-ILs. The methodology is based in the FCM, which has been used satisfactorily for the determination of thickness and roughness of intermediate layers in other materials. The thickness of AIN-IL is defined starting from the last monolayer of the first GaN phase to the last monolayer of the AlN phase.
