Velocity saturation effect in heterostructure field effect transistors

Heterostructure FETs fabricated on a doped InGaAs channel heterostructure yielded device performance superior to that of devices on a conventional superlattice MODFET structure. A comparison is made for 0.4-10-μm-gate-length FETs fabricated with a self-aligned gate process. Transconductance as high as 534 mS/mm was achieved with 0.4-μm doped channel devices. This device structure achieved better performance through electron velocity saturation during normal device operation. The MODFET structure, in contrast, is limited by charge transfer into the charge control layer and by gate leakage. Ring oscillators fabricated using 0.3 × 10 μm² gates on the doped channel structure yielded a minimum gate delay of 8.3 ps at 2.3 mW/gate.