A quantitative approach for trap analysis between Al(0.25)Ga(0.75)N and GaN in high electron mobility transistors

The characteristics of traps between the Al(0.25)Ga(0.75)N barrier and the GaN channel layer in a high-electron-mobility-transistors (HEMTs) were investigated. The interface traps at the Al(0.25)Ga(0.75)N/GaN interface as well as the border traps were experimentally analyzed because the Al(0.25)Ga(0.75)N barrier layer functions as a dielectric owing to its high dielectric constant. The interface trap density D(it) and border trap density N(bt) 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(it) value extracted by the conventional conductance method was 2.5 × 10(12) cm(−2)·eV(−1), which agreed well with the actual transistor subthreshold swing of around 142 mV·dec(−1). The border trap density N(bt) was also extracted from the frequency-dependent C–V characteristics using the distributed circuit model, and the extracted value was 1.5 × 10(19) cm(−3)·eV(−1). Low-frequency (1/f) noise measurement provided a clearer picture of the trapping–detrapping phenomena in the Al(0.25)Ga(0.75)N layer. The value of the border trap density extracted using the carrier-number-fluctuation (CNF) model was 1.3 × 10(19) cm(−3)·eV(−1), which is of a similar level to the extracted value from the distributed circuit model.