Temperature dependent substrate trapping in AlGaN/GaN power devices and the impact on dynamic ron

Temperature dependent substrate ramp measurements on AlGaN/GaN power high-electron-mobility transistors (HEMTs) are used to extract information on charge redistribution in the buffer structure as a function of substrate bias. The measurements are compared to a theoretical model, representing the ideal capacitive buffer stack. It is found that at room temperature some negative charge is stored in the buffer. However, at higher temperatures, positive charge storage occurs as a result of band-to-band tunneling through the GaN channel layer, suppressing bulk trap induced dynamic on-resistance.