IEEE TRANSACTIONS ON ELECTRON DEVICES 1 Sources of Transconductance Collapse in III–V Nitrides—Consequences of Velocity-Field Relations and Source/Gate Design

Abstract—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. Index Terms—GaN, HEMT, III–V nitrides, nonlinearity, transconductance collapse, velocity-field relations