Abstract
We report the RF power results of Sc(Al,Ga)N/GaN high electron mobility transistors (HEMTs). We show dc, small-signal RF and load-pull performance at 30 GHz with two barrier alloys-a ternary of ScAlN and a quaternary of ScAlGaN. The active layers are grown by molecular beam epitaxy on a GaN-on-SiC template. The Sc(Al,Ga)N HEMTs with 120 nm gate length achieve transconductance >700 mS/mm and >70 GHz cutoff frequency. The quaternary ScAlGaN sample shows reduced current collapse during pulsed I-V and load-pull characterization. The ScAlGaN HEMT delivers 5.77 W/mm output power (VD = 20 V) and 47% power-added efficiency (VD = 15 V) when tuned for maximum power and efficiency, respectively.
Highlights
N EXT-GENERATION GaN-based amplifiers require low sheet resistance and a thin barrier layer to meet efficient radio frequency (RF) power demands for millimeter-wave applications
Multiple approaches have accomplished this by adjusting the barrier alloy to increase the total polarization charge in the GaN channel with varying levels of piezoelectric charge such as in strained InAlN/GaN [1]–[3], AlN/GaN high electron mobility transistors (HEMTs) [4]–[6] as well as N-polar variations [7]–[9]
Latticematched In0.18Al0.72N/GaN HEMTs have been reported with performance in X and Ka-band but with limits on spontaneous induced sheet charge [10]–[12]
Summary
N EXT-GENERATION GaN-based amplifiers require low sheet resistance and a thin barrier layer to meet efficient radio frequency (RF) power demands for millimeter-wave applications. We report RF power performance of Sc(Al,Ga)N/GaN HEMTs. Two samples were grown by MBE with a ternary ScAlN and quaternary ScAlGaN barrier to compare the tradeoff in sheet charge density with respect to mobility as Ga is introduced. Two samples were grown by MBE with a ternary ScAlN and quaternary ScAlGaN barrier to compare the tradeoff in sheet charge density with respect to mobility as Ga is introduced These devices have improved short-channel effects over previously reported ScAlN/GaN HEMTs [20]. State-ofthe-art DC performance is reported for each while pulsed I-V and 30-GHz power sweeps indicate differences in current collapse between the two samples Both samples achieve >10 dB transducer gain (GT ) at 30 GHz. The quaternary ScAlGaN/GaN HEMT achieved 5.77 W/mm output power (POU T ) and 47% power-added efficiency (PAE) when tuned for optimal POU T and PAE, respectively. The early RF power performance nearly matches state-of-the-art Ga-polar devices at our reported frequency and bias conditions [9], [21]–[24]
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