Contactless electroreflectance evidence for reduction in the surface potential barrier in AlGaN/GaN heterostructures passivated by SiN layer

Abstract

Contactless electroreflectance (CER) has been applied to study the AlGaN potential-barrier height in AlGaN/GaN heterostructures without and with a SiN passivation layer. In the case of an unpassivated structure, an AlGaN band-edge signal with a strong Franz–Keldysh oscillation (FKO) was observed. On the basis of the FKO period, the surface potential barrier has been determined to be ∼1.1 eV. For the SiN passivated structure, a broad CER signal without FKO appears at the AlGaN edge. This observation is associated with a decrease in the height of the surface potential barrier, i.e., a shift in the Fermi level position at the AlGaN surface toward the conduction band.