Modulated precursor flow epitaxial growth of ternary AlGaN by metalorganic chemical vapor deposition

We report the growth of ternary AlGaN layers on AlN/sapphire substrates by modulated precursor flow epitaxial growth (MPEG) using metalorganic and hydride precursors. The ratio of group III input mole fraction was adjusted to control the group III composition of AlGaN layers. Atomically flat surface was observed at MPEG Al0.98Ga0.02N. In order to increase Ga mole fraction in AlGaN layers, the molar flow rate of gallium precursor increases up to 700%. The surface morphology of MPEG AlGaN layer became rough with large root-mean square (RMS) roughness values, while the Al composition in MPEG AlGaN just slightly decreased and still showed higher than 90%. It is suggested that gallium incorporation is limited by very low sticking coefficient of gallium atoms in MPEG growth condition used in this study and excess gallium input degrades the quality of AlGaN material.