Investigation of defect levels in Mg-doped GaN Schottky structures by thermal admittance spectroscopy

Schottky structures based on Mg-doped GaN layers grown by metalorganic chemical vapor deposition (MOCVD) on sapphire substrate are studied by thermal admittance spectroscopy from 90 K to room temperature. Evidence of two impurity levels results from the analysis of the observed peaks in the conductance curves, whose positions and strengths are temperature dependent. The experimental results are analyzed within a detailed theoretical study of the steady-state and small-signal electrical characteristics of the structure. Numerical simulations are based on the solution of the basic semiconductor equations for the structure consisting of two Schottky diodes connected back-to-back by a conduction channel formed by the GaN layer.