Sources of transconductance collapse in III-V nitrides - consequences of velocity-field relations and source/gate design

Experimental results from submicrometer devices in III-V nitride devices often exhibit a significant decrease in the transconductance when gate bias is increased. This creates new challenges for circuit design in III-V nitride technology. In this paper, we discuss possible sources of this collapse from a theoretical and computational standpoint. We find that polar optical phonon emission related velocity-field nonlinearities in 5-40 kV/cm region are the primary reason for the decrease in the transconductance. We also discuss possible solutions to this problem and examine the practicality of each solution. Shorter S/G spacing and higher doping in the source gate region are predicted to remove much of the transconductance collapse.