Comparison of C-Doped AlN/GaN HEMTs and AlN/GaN/AlGaN Double Heterostructure for mmW Applications

We report on a comparison of the ultrathin (sub-10 nm barrier thickness) AIN/GaN heterostructure using two types of buffer layers for millimeter-wave applications: 1) carbon doped GaN high electron mobility transistors (HEMTs) and 2) double heterostructure field effect transistor (DHFET). It is observed that the carbon doped HEMT structure shows superior electrical characteristics, with a maximum drain current density Id of 1.5 A/mm, an extrinsic transconductance Gm of 500 mS/mm and a maximum oscillation frequency f
_max
of 242 GHz while using a gate length of 120 nm. The C-doped structure delivering high frequency performance together with an excellent electron confinement under high bias enabled to achieve a state-of-the-art combination at 40 GHz of output power density (POUT = 7 W/mm) and power added efficiency (PAE) above 52% up to VDs = 25V in pulsed mode.