Intrinsic transit delay and effective electron velocity of AlGaN/GaN high electron mobility transistors

A delay time analysis was carried out for AlGaN/GaN high electron mobility transistors (HEMTs) with gate lengths of 120-210nm. The influence of the large parasitics in the access region is counted out by de-embedding these parasitics from the measured parameters. From the obtained intrinsic transit delay, the effective electron velocity is estimated to be 1.86 × 107 cm/s. The parasitic delay is rather a major cause of delay in the devices tested. We also found that the channel charging time is not negligible even at the gate length of 120nm, whereas it can be in the InP HEMTs with the same gate length.