Recessed-gate quasi-enhancement-mode AlGaN/GaN high electron mobility transistors with oxygen plasma treatment

In this paper, the enhancement-mode AlGaN/GaN HEMT combined with the low damage recessed-gate etching and the optimized oxygen plasma treatment was fabricated. Scanning electron microscope/energy dispersive spectrometer (SEM/EDS) method and x-ray photoelectron spectroscopy (XPS) method were used to confirm the formation of oxides. Based on the experimental results, the obtained enhancement-mode HEMT exhibited a threshold voltage of 0.5 V, a high peak transconductance of 210 mS/mm, and a maximum drain current of 610 mA/mm at the gate bias of 4 V. Meanwhile, the on/off current ratio of enhancement-mode HEMT was as high as 10⁸, drain induced barrier lowering (DIBL) was as low as 5 mV/V, and subthreshold swing (SS) of 80 mV/decade was obtained. Compared with the conventional HEMT, the Schottky reverse current of enhancement-mode HEMT was three orders of magnitude lower, and the off-state breakdown voltage of which was higher. In addition, a power gain cutoff frequency (f_max) of the enhancement-mode HEMT was larger than that of the conventional one.