AlxGa1−xN/GaN heterostructure field-effect transistors (HFETs) with different Al mole fractions were grown on sapphire substrates. With a 5-nm-thick undoped AlxGa1−xN spacer layer and a 14-nm-thick Si-doped AlxGa1−xN layer, it was found that we achieved the largest product value of sheet carrier concentration and electron mobility from the sample with an Al mole fraction of 0.32. Due to the insertion of an Mg-doped GaN layer, it was found that all samples exhibit good pinch-off characteristics. With a 1-μm-gate length, the measured saturation IDS were 207, 270, 430, and 355 mA/mm while the maximum gm were 84, 129, 165, and 137 mS/mm for samples with an Al composition of 0.22, 0.26, 0.32 and 0.36, respectively.
Journal of Crystal Growth / Volume 275, Issues 3–4, Pages398–403