Vertical tunnel field-effect transistor with bandgap modulation and workfunction engineering

A molecular beam epitaxy grown vertical tunnel field-effect transistor based on hand-to-hand tunneling has already been proposed. Based on silicon, it showed some remarkable properties. However, it failed to meet the technology requirements in terms of on-current and threshold voltage. Improvement in the n-channel device performance by bandgap modulation at the tunneling junction using a thin deltap(+) SiGe layer has been shown. However, as the germanium mole fraction, x, is increased in SiGe, even though the on-current, I-on, threshold voltage, V-T, and sub-threshold swing, S, all show improved behavior, the leakage currents, I-off, is seen to increase significantly as tunneling probability becomes significant even at zero gate bias. In this work, we further present the improvement in the device performance using gate workfunction engineering along with bandgap modulation at the tunnel junction. As bandgap modulation leads to improved S and can be scaled to below 60 mV/dec independent of temperature, T, we show, by means of 2-D computer simulations that it is possible to achieve very low off-currents and very high on-currents for the tunnel FET.