Through-layer XPS investigations of the Si3N4/AlGaN interface

Investigations of chemical species at the dielectric/III‐N interface remain an important question in order to understand the chemical origin of the surface states, which are present at the heterostructure surface. In this work, we demonstrate a sample preparation technique to analyze the existing interface species by X‐ray photoelectron spectroscopy (XPS) through thin uniform silicon nitride (Si3N4) layers 1.4 ± 0.2 nm. We show that it is crucial that the layers are as thin as possible but as thick as necessary to avoid oxygen diffusion through the passivation. Due to the sufficient information depth provided by such layers, the photoelectrons are detected. This is an advantage over sputtering as no intermixing of atoms or cleavage of bonds occurs. We show that the deposited Si3N4 hinders oxygen diffusion through the layer to the AlGaN surface. Selective SiO2 over Si3N4 etching and XPS depth profiles indicate that ∼1 nm of the thin Si3N4 layer has formed a surface oxide. Angle‐resolved XPS measurements confirm the accumulation of oxygen at the top and bottom Si3N4 interfaces. No indication is found that interfacial oxygen is bound to any other than the group‐13 metal. In agreement with the HSAB concept, the interfacial oxygen is bound to Al rather than Ga. Scheme of the nondestructive XPS interface analysis of the dielectric/AlGaN interface.