Theoretical investigation of the charges weight between interface and the oxygen traps in barrier layer on the 2DEG density of $$\hbox {Al}_{2}\hbox {O}_{3}$$ Al 2 O 3 /AlGaN/GaN HEMTs

Abstract

Unintentional impurities like oxygen introduced into the undoped AlGaN barrier may present an important traps source for these devices besides $$\hbox {Al}_{2}\hbox {O}_{3}$$ /AlGaN interface traps. Here, we present a theoretical study of the charges weight between oxygen traps in barrier layer and $$\hbox {Al}_{2}\hbox {O}_{3}$$ /AlGaN interface traps on the 2DEG density for different gate bias. In order to conduct this study, a semi-analytical 1D charge model has been developed and used based on the nonlinear Poisson and Schrodinger coupled equations. The model is based on a new analytical expression of the electric field distribution under the gate including the ionized oxygen profile into the AlGaN barrier. A secondary ion mass spectrometry and deep-level transient spectroscopy measurements on a fabricated device were performed. A mean density of oxygen up to $$2\times 10^{18}\,\hbox {cm}^{-3}$$ was measured into the AlGaN barrier, associated with an activation energy of 0.44 eV and a cross section of 1.4 $$\times 10^{-14 }\,\hbox {cm}^{2}$$ . Using these values as the model inputs, the theoretical results showed that even with changing the balance between the interface states density and the barrier traps density, there is no an absolute traps domination either from the barrier or the interface traps and their impact weight on the 2DEG density changes with the gate bias.