Excitation mechanisms and structure-related Er3+ emission in amorphous and nanocrystalline GaN films

We report on Er3+ luminescence at room temperature in the visible and infrared regions in amorphous GaN:Er films prepared by DC magnetron co-sputtering. The intensity of the Er3+ luminescence at 1535 nm corresponding to the 4I13/2→4I15/2 transition increased after annealing at 750°C. During annealing GaN crystallites form in the amorphous matrix. The crystallite diameters are between 4 and 7 nm as analyzed by high-resolution transmission electron microscopy (HRTEM). A shallow exponential absorption edge extends three orders of magnitude in absorption coefficient over the spectral range from 0.5 to 3.5 eV. On this exponential absorption are superimposed the resonant absorption bands of Er3+ ions.