I have a MOSFET fabricated on p-type substrate with semiconductor SWCNT channel having source and drain contacts of semiconductor material. Between source and drain high-k dielectric is there over which SWCNTs are placed. For the drain voltage (Vd) sweep from negative to positive biases, it is seen that the Id or drain current increases in negative values while it increases in positive values for positive drain biases for the different applied gate biases. What does the negative Id indicates for negative drain biases or Vd. What is the major charge carrier in this case ?