The IV characteristic and Schottky barrier energy band diagram below depict the operation of a p-type CNTFET.   A p-type FET operates directly opposite that of the n-channel FET.   The main charge carriers are holes, so to induce a channel in a normal p-channel MOSFET, a sufficient negative voltage needs to be applied to the gate.   A positive voltage will repel the holes in the channel to deplete the channel of holes and disable the FET from conducting current.   Likewise, the energy band diagram structure for the metal-semiconductor junction is the opposite of the case of the n-type CNTFET discussed previously.   When a larger negative voltage is applied to the gate, the band structure shifts up (the solid line is the most positive voltage).   As the voltage becomes more negative (larger in magnitude), the width of the Schottky barrier decreases and holes as opposed to electrons will tunnel through the energy barrier in the valence band.  


left:  graph courtesy of Phaedon Avouris, Applied Physics Letters, vol 73, p. 2447 (1998)
right:  diagram from S. Heinze, J. Tersoff, R. Martel, et al., Phys. Rev. Lett. 89, 106801 (2002).