I have shared my code and curve picture in comment section

From the device graph characterstics it is displaying heavy leakge current which is possible due to

1. Gate is unable control the device- Add appropriate workfunction to Gate.

2. Heavy doping- Apply doping moderately and then increase linearly and see at what point gate is leaking.

I add gate work function=5.25. And for doping i have started from 1^16 and increase linearly to 1^18. But getting something like this-

Kindly @Fahim Shahriar fine tune the model, mesh desgin and doping profile. Simulate the code line by line and undestand the physics for better understanding