Composite channel HEMTs for millimeter-wave power applications

The InGaAs-InP composite channel HEMT is an interesting way to overcome the strong impact ionization in the InGaAs channel which is one of the main limitations of InP based HEMT. We present in this paper an experimental quantification of improvements provided by a composite channel. Using an InGaAs/InP composite channel, device output conductance was reduced from 145 mS/mm to 85 mS/mm, transconductance was enhanced from 1 S/mm to 1.2 S/mm and cut-off frequency f/sub MAX/ increased by 50%. Influence of the feedback capacitance on RF performance has also been investigated through the comparison of passivated and nonpassivated devices. So, 0.15 /spl mu/m gate length InGaAsInP composite channel HEMT show an f/sub T/ of 151 GHz and an f/sub MAX/ of 225 GHz. We also present state of the art power performance at 60 GHz of an InGaAs/InP/n+-InP composite channel HEMT which exhibits an output power density of 355 mW/mm, 12% power-added-efficiency (PAE) and 6.2 dB of linear gain.