Extension p-Doping of Carbon Nanotube Transistors through Nitric Oxides Annealing

This work investigates the p-doping effect of Nitric Oxides (NO_<i>X</i>) annealing on transistors with a channel from a network of carbon nanotubes (CNTs), with a focus on extension doping of top-gated transistors and RF characterization. NO_<i>X</i> annealing at 100 °C for 1 h induces oxidation in CNTs, which introduces a doping band inside the nanotube band gap near the valence band. The benefits and drawbacks of NO_<i>X</i> annealing on the performance of back-gated (BG) CNT transistors are characterized. The doping band is beneficial in that it reduces the Schottky barrier for hole injection and increases the hole carrier concentration in the channel. However, we also note that NO_<i>X</i> annealing deteriorates the inverse subthreshold swing (SS) and drain-induced barrier lowering (DIBL) by introducing interface traps and worsens any existing short channel effects. Our capacitance analysis confirms that the increase in source-drain and interface-trap capacitances degrades both SS and short channel effects. To circumvent the drawbacks of NO_<i>X</i> annealing, we employ it to create extension doping regions in p-type, top-gated transistors with a scaled high-k gate oxide, leading to an increase in drain current from 5.09 to 13.95 μA at <i>V</i>_OV = -2 V and <i>V</i>_DS = -1 V. Because the effect of NO_<i>X</i> annealing is limited to the extension regions and has little impact on the channel region, negative effects on the SS and DIBL are mitigated. Finally, an RF transistor is fabricated, and NO_<i>X</i> annealing is used to enhance the cutoff frequency by approximately 10-fold.