Demonstration of a velocity modulated transistor

We report the design, fabrication and initial testing of the first velocity modulation transistor (VMT), a high speed device proposed by Sakaki in 1982. Our VMTs are built on a GaAs/Al/sub x/Ga/sub 1-x/As heterostructure with 70 nm separating a high mobility 2 dimensional electron gas (2DEG) and a lower mobility, doped channel grown at a slightly reduced temperature. The mobility ratio between the 2DEG and the low mobility channel was measured to be 2.5:1 at 300 K when the channels are both fully populated. Real space transfer, which is central to the operation of the VMT, has been verified in the heterostructure under DC operation using a three-gated device created for this purpose. We have fabricated a VMT structure with top and bottom gates and performed DC measurements to determine optimum operating conditions.