Gate leakage characteristics of the DG-nTFET, showing (a) barrier height dependence: higher barrier can effectively reduce the hot-carrier injection current; (b) redirection mean free path dependence: leakage floor can be limited by longer redirection distance; (c) scattering mean free path in semiconductor: the scattering rate of hot-carrier would be increased by increasing the scattering path; (d) scattering length dependence in the image-force potential well: this effect is similar to electron traveling a distance in semiconductor, but it is not obvious; (e) SS versus drain current for different free paths, barrier heights and image-forces.