Novel quaternary AlInGaN/GaN heterostructure field effect transistors on sapphire substrate

Undoped quaternary AlxIn0.02Ga0.98-xN/GaN heterostructure field effect transistors (HFET) with different Al mole fractions were fabricated on sapphire substrate. An enhancement in two-dimensional electron gas density with increasing the Al mole fractions was observed. The properties of HFETs revealed that, with the Al incorporation, both maximum transconductance (gmmax) and drain current (Idmax) increased up to 138 mS/mm and 1230 mA/mm, respectively, for the device with 2 µm gate length. In addition, the threshold voltage strongly depended on Al mole fraction, by which normally-off HFET was demonstrated on a low Al-contained sample. No breakdown was observed for all the AlxIn0.02Ga0.98-xN/GaN HFETs when the gate–drain reverse bias was applied up to 100 V. The results indicate that quaternary AlInGaN is a promising candidate for high power and high frequency device applications.