In solid state physics the Ridley–Watkins–Hilsum theory (RWH) explains the mechanism by which differential negative resistance is developed in a bulk solid state semiconductor material when a voltage is applied to the terminals of the sample.
It is named for British physicists Brian Ridley,[2] Tom Watkins and Cyril Hilsum who wrote theoretical papers on the effect in 1961.
While this transfer occurs, the material exhibits a decrease in current – that is, a negative differential resistance.
Of the type of semiconducting materials satisfying these conditions, gallium arsenide (GaAs) is the most widely understood and used.
However RWH mechanisms can also be observed in indium phosphide (InP), cadmium telluride (CdTe), zinc selenide (ZnSe) and indium arsenide (InAs) under hydrostatic or uniaxial pressure.