Dynamics of the Kink Effect in

InA1As/InGaAs/InP High Electron Mobility Transistors (HEMTs) show significant promise for low-noise and high-power millimeter-wave applications (60 GHz and above). Unfortunately, these HEMTs show a detrimental behavior in their output characteristics, the kink effect. The kink is a sudden rise in drain current at a certain drain-to-source voltage that results in high drain conductance and transconductance compression, leading to reduced voltage gain and poor linearity. In this study we report the first experimental pulsed measurements of the dynamics of the kink effect in InA1As/InGaAs/InP with nanosecond resolution. Our measurements show that the kink turns on first the higher VDS is. The rate at which the kink builds-up is seen to increase with both VDS and VGs. In general, the kink's characteristic time constant strongly depends on both VDS and VGS: for small values of VDG, it decreases exponentially with VDG; on the other hand, for large values of VDG, it becomes independent of VDG. Values between 50 ns and 100 1ps have been measured in a single device. This suggests that, from a small signal point of view, the kink should not be visible in the millimeter-wave range. Our research also shows that the kink is related to impact ionization that takes place in the high-field region at the drain end of the channel. We have found that the rate at which the kink builds-up in its early stages follows a classical 1/(VDs-VDS,SAT) dependence characteristic of impact ionization. Our data should be instrumental in formulating a hypothesis and building a model for the physical origin of the kink. Thesis Supervisor: Jesus A. del Alamo Title: Associate Professor