Room-temperature photoluminescence of Mg-doped GaN thin films grown by plasma-assisted MOCVD

The growth of Mg-doped GaN thin films by metalorganic chemical vapor deposition (MOCVD) using NH3 and Cp2Mg as a source of nitrogen and Mg, respectively, usually produces Mg-H complexes, which hinder the activation of Mg as shallow acceptor centers. Therefore, post-growth treatments are commonly required to activate these acceptor centers. The presence of Mg dopants in GaN films induces various defect-related emissions whose characteristics depend on the growth method. For this study, we prepared Mg-doped GaN thin films by plasma-assisted MOCVD. A nitrogen-plasma, instead of NH3, served as a nitrogen source to minimize the formation of Mg-H complexes, thereby eliminating the requirement for post-growth treatment. The emission characteristics were obtained by measuring the photoluminescence of the as-grown room-temperature films. Yellow, green, blue, and ultraviolet emission bands are produced by Mg-doped samples with different Mg concentrations produced by Cp2Mg flow rates of 2%, 5%, and 10% of the total flow rate. Low-Mg concentration leads to nitrogen and gallium vacancies, which results in yellow photoluminescence. At higher Mg concentration, the yellow photoluminescence is suppressed and the blue photoluminescence is enhanced because of the incorporation of vacancies by Mg atoms. The analysis of the photoluminescence spectra leads to the proposed band diagrams for Mg-doped GaN with varying Mg concentration.