Design of insulator/AlGaN structures in MIS AlGaN/GaN HFETs for higher device performance

摘要

To improve the device performance of GaN-based Metal-Insulator-Semiconductor (MIS) heterostructure field-effect transistors (HFETs), the layer design of MIS AlGaN/GaN HFETs has been investigated by considering the insulator/AlGaN structures as the total barrier layers of MIS HFETs. Since deposition of insulators on AlGaN has proven to change electrical properties of the heterostructures as the increase in AlGaN thickness does, considering the insulator/AlGaN structures as the total barrier layers is effective and indispensable in designing the MIS AlGaN/GaN HFETs. With an increased insulator thickness and decreased AlGaN thickness, where the gate capacitance is kept constant, a high transconductance was successfully obtained that was equivalent to that of HFET, in addition to the reduced gate leakage current in MIS HFETs. Moreover, Al_2O_3-based MIS HFETs were revealed to exhibit superior DC characteristics over conventional Si_3N_4 MIS HFETs, which can be ascribed to larger bandgap energy of Al_2O_3 than Si_3N_4 . Channel doping design has also been proposed to incorporate into MIS HFETs to modulate the threshold voltage aiming at the same application of depression mode as conventional HFETs. In a MIS HFET with channel doping design, a significantly reduced gate leakage current was obtained with a transconductance and threshold voltage mat are kept close to typical values of HFETs, indicating that the device has a potential to replace conventional HFETs. Thus, design of insulator/AlGaN structures and incorporation of channel doping design are the key, with which MIS HFETs exhibiting a low gate leakage current and high transconductance with a desired threshold voltage can be realized.