Short-channel effects occur when the channel length is the same order of magnitude as the depletion-layer widths of the source and drain junction. In MOSFETs, channel lengths must be greater than the sum of the drain and source depletion widths to avoid edge effects. Otherwise, a number of effects appear.
Among the reported effects cited by a number of researchers at universities around the globe are:
1. "Off-state" leakage current.
2. Impact ionization, in which a charge carrier can be affected by other charge carriers;
3. Velocity saturation/mobility degradation;
4. Drain-induced barrier lowering (DIBL), which is caused by encroachment of the drain depletion region into the channel;
5. Drain punch through, whereby current flows regardless of gate voltage—a phenomenon that can occur if the drain is at high enough voltage compared to the source and the depletion region around the drain extends to the source;
6. . Surface scattering;
7. Channel length modulation;
8. Threshold voltage roll-off.