Determination of the Self-Compensation Ratio of Carbon in AlGaN for HEMTs

Epitaxial AlGaN/GaN/AlGaN-on-Si high-electron mobility structures with and without carbon doping have been studied. By considering the donor density required to suppress a 2D hole gas in the undoped structure, we demonstrate that the 2 × 10¹⁹ cm^-3 substitutional carbon incorporated during metal-organic chemical vapor deposition must be a source of donors as well as acceptors, with a donor to acceptor ratio of at least 0.4. This compensation ratio was determined based on the comparison of substrate bias experiments with TCAD simulations. This value, which was previously unknown, is a key parameter in GaN power switching high-electron-mobility transistors, since it determines the resistivity of the layer used to suppress leakage and increase breakdown voltage.