N-Polar GaN/AlN MIS-HEMT for Ka-Band Power Applications

In this letter, we demonstrate the millimeter-wave power performance from N-polar GaN-based metal-insulator-semiconductor high-electron-mobility transistors. The device consists of a GaN spacer structure with an AlN barrier to reduce the alloy scattering. High Si doping in GaN without excessive surface roughening has been achieved using a digital doping scheme with a low ohmic contact resistance of 0.16 Ω·mm. An fT and an f_MAX of 56 and 130 GHz, respectively, were obtained for a 150-nm gate length. A peak output power of 1.9 W/mm with a power-added efficiency (PAE) of 14% was achieved for V_DS = 20 V, and a peak output power of 2.2 W/mm with a 12% efficiency and a linear transducer power gain of 5.7 dB was achieved for V_DS = 30 V at 30 GHz. The cause of the low PAE was determined to be due to the current collapse from the RF-IV measurements, and remedies have been suggested to minimize the dc-RF dispersion.