Surface potential analysis of AlN/GaN heterostructures by electrochemical capacitance-voltage measurements

AlN/n⁺-GaN heterostructure samples with AlN barrier layer thickness between 1 nm and 4 nm have been analyzed by electrochemical capacitance-voltage measurements with a semiconductor-electrolyte contact to estimate the surface potential of this heterostructure. The combination of using a semiconductor-electrolyte interface for characterization and using an n⁺-doped GaN buffer layer enabled the extraction of the surface potential from the full range of date between the two flatband conditions, flatband in the AlN barrier and flatband in the GaN buffer. Such analysis is otherwise difficult to obtain due to the tunneling restriction. In the present case of an AlN/GaN heterostructure, the analysis leads to a surface potential of ∼1.9 eV, independent of the AlN barrier layer thickness.