Undoped AlInGaNGaN heterostructure field-effect transistors (HFETs) have been demonstrated on sapphire substrate. The maximum drain current of 758 mAmm and extrinsic transconductance of 123 mSmm were obtained from the device with 2 μm gate length and 15 μm gate width. Such performance was comparable to that of a conventional modulation-doped (MOD) AlGaNGaN HFET fabricated at same the condition. In spite of the high-density two-dimentional electron gas formed at the heterointerface, the AlInGaNGaN HFET structure showed relatively low Hall mobility (689 cm2 V s at 300 K), which was due to the high concentration background doping in the undoped AlInGaN barrier region. Encouragingly, both the gate leakage current and drain current collapse showed lower values than that of the MOD-AlGaNGaN HFET, which implied the potential application of quaternary AlInGaN to high-power and high-frequency devices.
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