Abstract: High performance microwave GaN-on-SiC HEMTs are demonstrated on a heterostructure without a conventional thick doped buffer. The HEMT is fabricated on a high-quality 0.25 μm unintentional doped GaN layer grown directly on a transmorphic epitaxially grown AlN nucleation layer. This approach allows the AlN-nucleation layer to act as a back-barrier, limiting short channel effects and removing buffer leakage. The devices with the `buffer-free’ heterostructure show competitive DC and RF characteristics, as benchmarked against the devices made on a commercial Fe-doped epi-wafer. Peak transconductances of 500 mS/mm and a maximum saturated drain current of ~1 A/mm are obtained. An extrinsic f T of 70 GHz and f max of 130 GHz are achieved for transistors with a gate length of 100 nm. Pulsed-IV measurements reveal a lower current slump and a smaller knee walkout. The dynamic IV performance translates to an output power of 4.1 W/mm, as measured with active load-pull at 3 GHz. These devices suggest that the `buffer-free’ concept may offer an alternative route for high frequency GaN HEMTs with less electron trapping effects.
Published in: IEEE Electron Device Letters ( Volume: 41, Issue: 6, June 2020)