A quantitative approach for trap analysis between AlGaN and GaN in high electron mobility transistors.

The characteristics of traps between the AlGaN barrier and the GaN channel layer in a high-electron-mobility-transistors (HEMTs) were investigated. The interface traps at the AlGaN/GaN interface as well as the border traps were experimentally analyzed because the AlGaN barrier layer functions as a dielectric owing to its high dielectric constant. The interface trap density D and border trap density N were extracted from a long-channel field-effect transistor (FET), conventionally known as a FATFET structure, via frequency-dependent capacitance-voltage (C-V) and conductance-voltage (G-V) measurements. The minimum D value extracted by the conventional conductance method was 2.5 × 10 cm·eV, which agreed well with the actual transistor subthreshold swing of around 142 mV·dec. The border trap density N was also extracted from the frequency-dependent C-V characteristics using the distributed circuit model, and the extracted value was 1.5 × 10 cm·eV. Low-frequency (1/f) noise measurement provided a clearer picture of the trapping-detrapping phenomena in the AlGaN layer. The value of the border trap density extracted using the carrier-number-fluctuation (CNF) model was 1.3 × 10 cm·eV, which is of a similar level to the extracted value from the distributed circuit model.