Al concentration control of epitaxial AlGaN alloys and interface control of GaN/AlGaN quantum well structures

Al x Ga 1−x N alloys were grown by metalorganic chemical vapor deposition on c-plane sapphire substrates under various growth conditions. Both the Al concentration and the growth rate of AlGaN are strongly affected by gas-phase parasitic reaction between ammonia and group-III sources. As the ammonia flow rate increases with fixed flow rate of group-III sources, both the Al concentration in the solid and the growth rate of AlGaN are decreased. It was also found that the Al concentration in the solid saturated as increasing the Al gas composition increased by increasing the flow rate of the Al source precursor. In addition, the influence of growth interruption when group-III sources are temporarily shut off on the optical quality of GaN/AlGaN single quantum well (QW) structures was studied to realize high-quality QWs. Photoluminescence measurements revealed that the emission peak is blueshifted as the interruption time increases and the emission intensity is maximized at a several-second short interruption time, indicating the GaN QW layer is evaporated during interruption at a high growth temperature.