Fabrication and characterization of GaN-based nanostructure field effect transistors

Two different types of GaN-based nanostructure FETs, such as FinFETs and gate-all-around (GAA) nanowire FETs, have been investigated along with discussing their important performances for a possible new application. The GaN-based FinFETs have better electrostatic control compared to conventional planar-type GaN-based HEMTs, which offers great performance improvement such as very low off-state leakage current, high breakdown voltage, high linearity with broad transconductance. Recent investigation demonstrated that an appropriately designed AlGaN/GaN-FinFETs could exhibit low saturation drain voltage and very fast switching characteristics with subthreshold swing of sub-60 mV dec, which indicates that they can be a promising candidate for low voltage/power logic application. GAA GaN nanowire FETs have even better electrostatic control and exhibit excellent device performances showing their potential low voltage/power logic applications. For clear understanding of the device performances, simulation including two models concerning the multi-level trapping effects and the self-heating effects has been conducted, which leads to good agreement with the experimental results. Negative transconductance and offset-like output characteristics, observed in the narrow nanowire devices, have been well explained using the deep trapping effect and the built-in potential at ohmic contact. Scaling of the nanowire FET has been implemented such as channel length, doping concentration, and diameter of nanowire, which helps to predict further improvement of the device performance.