Gate leakage mechanisms of the AlGaN/GaN HEMT with fluorinated graphene passivation

The AlGaN/GaN high-electron-mobility transistor (HEMT) passivated by fluorinated graphene (FG) has been investigated. The performances of the HEMTs without passivation before and after F plasma treatment, with FG, Silicon nitride (SiNx), FG/SiNx passivation were contrasted. Compared with the HEMT without F plasma treatment and passivation, the gate leakage current decreases one and a half orders of magnitude after F plasma treatment and SiNx passivated, and four orders of magnitude after FG and FG/SiNx passivated. To study the leakage mechanisms, the temperature dependences of gate leakages have been tested at 323 K-473 K. Through analysis and fitting, the leakages are composed of three components, which are thermionic emission (TE) current, two-dimensional variable range hopping (2D-VRH) current, and Fowler-Nordheim tunneling (FNT) current. TE dominates in the high forward bias region. 2D-VRH dominates in low forward bias. And the chief leakage mechanisms at reverse bias are 2D-VRH and FNT. At 473 K, Schottky barrier height of the HEMT with FG passivation is 1.21 eV. The activation energy and the effective barrier height on the HEMT with FG passivation are 0.64 eV and 0.33 eV respectively. Furthermore, the reasons for the decrement of the gate leakage on the HEMT with FG and FG/SiNx passivation are the enhancement of Schottky barrier heights and augmentation of activation energy. And the improvement in gate leakages for the HEMT passivated by FG/SiNx mainly results from the effect of FG.