how the parameters affect the threshold voltage, leakage current and drain current???
I mean: e.g. when increase the doping concentration, how the charge inside the transistor changes its threshold voltge and leakage current and drain current???
Increasing doping concentration means that you are placing more charge carriers. More charge carriers mean that your device will be able to handle more current, therefore increasing drain current capacity. It also means that more carriers have to recombine so the leakage current will increase. I'm not so sure about the threshold voltage, though. But I think it will decrease.