The effect of growth temperature on the luminescence and structural properties of gan : tm films grown by gas-source mbe

During molecular beam epitaxy of GaN:Tm films, substrate temperature strongly influences the rare earth incorporation, surface morphology and luminescence spectrum. The Tm incorporation into films grown between 730 and 830 °C was estimated by wavelength-dispersive X-ray (WDX) spectroscopy. Comparative WDX, atomic force microscopy (AFM) and cathodoluminescence (CL) mappings reveal that at an optimal growth temperature between 775 and 780 °C, a high Tm content (2.2 at%) and a smooth surface morphology can be obtained, leading to an intense sharp Tm3+ emission. For lower substrate temperatures, Ga droplets and large (8-15 μm) circular pits mar the sample surface; for higher temperatures, the sharp CL lines disappear due to low Tm content (0.8 at%).