High Performance of AlGaN/GaN HEMTs using Buffer-Free GaN on SiC Structure

This paper reports on the processing and device characteristics of AlGaN/GaN high electron mobility transistors using buffer-free GaN grown on SiC substrate. This new concept of thin AlGaN/GaN heterostructure (<330nm of epitaxial layers) as compared to a conventional structure with a thick GaN buffer layer (>2-3μm). As-grown epitaxial structure provides a twodimensional electron gas (2DEG), ns, of 1 x 1013 cm-2 , an electron mobility, µ, of > 2000 cm2 /V.s, and sheet resistance, Rsh, of 330 Ω/□. The fabricated AlGaN/GaN HEMT buffer-free GaN with a 3-μm gate long, two-finger 2 × 50 µm wide device demonstrates a maximum drain current density of 801 mA/mm at VGS = 2 V and maximum peak transconductance of 189 mS/mm at VDS = 5 V. This device also produces low gate leakage currents of IGS = 2.1x10-4 A/mm at VGS = -10 V and a breakdown voltage, VBR, of over 200 V. The maximum cut-off frequency, fT, and maximum oscillation frequency, fmax, of 4.7 GHz and 9.4 GHz were obtained respectively. These results indicate the potential of using buffer-free GaN heterostructure for future high power high frequency applications