) is on the order of the charge carrier’s mean-free path length (MFPL) in the material the electrons can be considered to move  ballistically. Carriers moving from the left to right either pass directly through the neck or collide against the angled edge and eventually channel through the neck. On the right hand side, most of the carriers are blocked and reflected away from the neck by the  vertical blocks. The neck is required to be of the order of the MFPL, otherwise the probability of electrons passing in reverse direction will increase significantly and compromise the rectification performance. In most metals, the electron MFPL is around 10-30 nm around room temperature [21], so