Unravelling the unwanted Ga incorporation effect on InGaN epilayers grown in CCS MOVPE reactors

Abstract

We show that gallium pollution in an AIXTRON Close Coupled Showerhead (CCS) Metal-Organic Vapor Phase Epitaxy (MOVPE) reactor can strongly affect the growth process stability of InGaN layers. By comparing growth with and without gallium pollution from the showerhead, we find a decrease in the indium incorporation and an increase in layer thickness of up to three times when the pollution is present. This phenomenon varies with the quantity of gallium on the showerhead, with increased gallium due to thicker GaN growth causing a stronger effect. Higher TMIn flows also give a more pronounced effect. These data support our previous hypothesis of TMIn reacting with metallic gallium present on the showerhead surface to release TMGa, which is then incorporated as Ga into the grown layers. This study of the effect of gallium contamination on InGaN layers in CCS MOVPE reactors leads us to suggest that the growth in CCS reactors should be performed free from gallium pollution to give more stable and comprehensible results.