Yellow luminescence and hydrocarbon contamination in MOVPE-grown GaN

Photoluminescence (PL) and cathodoluminescence (CL) measurements were performed on GaN films grown by metal organic vapor phase epitaxy (MOVPE) in order to study the origin of the yellow luminescence (YL) in this material. The development of the YL was followed as a function of deposition temperature between 650 and 1100 °C, in relation with the microstructure and the contamination in carbon, oxygen, and hydrogen determined by thermal effusion measurements. The YL was found to emanate from the grain boundaries, where high concentrations of hydrocarbons are present. This contamination could be removed upon thermal annealing up to 400 °C, whereas the YL remained constant. Thermal treatments up to 1000 °C increased the YL by a factor of 1.5. Since GaN decomposes above (850 ± 20) °C by evaporation of nitrogen molecules, the participation of nitrogen vacancies in the YL mechanism is suggested.