Deep Level Transient Spectroscopy (DLTS) is a powerful tool for the study of electrically active defects (known as traps) in semiconductors, due to contamination.   DLTS is a destructive technique, as it requires forming either a Schottky diode or a p-n junction with a small sample, usually cut from a complete wafer.  

Majority carrier traps are observed by the application of a reverse bias pulse, while minority carrier traps can be observed by the application of a forward bias pulse. 

The technique works by observing the capacitance transient associated with the change in depletion region width as the diode returns to equilibrium from an initial non-equilibrium state.