Direct Current and Radio Frequency Characterizations of AlGaN/AlN/GaN/AlN Double‐Heterostructure High‐Electron Mobility Transistor (DH‐HEMT) on Sapphire

The AlGaN/AlN/GaN/AlN double‐heterostructure high‐electron mobility transistor (DH‐HEMT) on sapphire substrate is introduced, and its direct current (DC) and radio frequency (RF) characteristics to the conventional GaN‐based single‐heterostructure HEMT (SH‐HEMT) on SiC substrate are compared. The devices having the two‐finger gate are fabricated with gate width of 200 μm and gate length of 500 nm. The DC performance of the DH‐HEMT shows a transconductance of 0.233 S mm −1 and a maximum drain current density of 0.93 A mm −1 , comparable with that of the SH‐HEMT. There is less‐pronounced kink‐effect in the DC I – V characteristics, whereas the off‐state subthreshold current is approximately four orders of magnitude higher than that of SH‐HEMT. A pulsed I – V shows a greatly suppressed slump ratio Z 1 and Z 2 of 1.6% and 4.3% for the DH‐HEMT. It is shown that the performances of a small‐ and a large‐signal characteristics of the DH‐HEMT are equivalent to the GaN SH‐HEMT: the current gain cutoff frequency ( f T ) and the maximum oscillation frequency ( f max ) are 20.1 and 47.6 GHz, and the output power density and the power added efficiency (PAE) at the peak PAE, at 20 V drain voltage and 3.5 GHz frequency, are 3.83 W mm −1 and 57.2%, respectively.