A Scaling Study of Excess OFF-State Current in InGaAs Quantum-Well MOSFETs

A scaling study of excess OFF-state current in planar InGaAs quantum-well MOSFETs is reported. We find that pure band-to-band tunneling (BTBT) dominates the drain OFF-state current in devices with channel length above ~1 μm. In this regime, the drain-gate voltage sets the rate of BTBT. In devices with channel lengths below 1 μm, a parasitic bipolar transistor effect becomes relevant. The bipolar current gain is found to scale inversely with the effective channel length for Lg between 70 nm and 1 μm, as expected from simple bipolar transistor theory. For Lg below ~70 nm, the OFF-state current increases rapidly due to an enhancement in bipolar current gain as a result of strong short-channel effects and punchthrough. Current gains in excess of 104 have been observed. A reduction in channel thickness decreases both BTBT and the bipolar gain effect.