An investigation of transient negative resistance in a cadmium sulfide device

An analysis has been made of a CdS device which exhibits a transient negative resistance at room temperature and low field strengths whereas previously reported cases of negative resistance in CdS were observed at low temperatures and moderate to high electric fields. The CdS bar was illuminated on one end in the vicinity of an ohmic In contact. Contact was made to the other end of the device with a rectifying Ag contact and the device was reverse biased. Experimental evidence and the analytical results both indicated that it is necessary that the material used to make the negative resistance devices must have a relatively low carrier mobility, high trap density, and a low regeneration rate for trapped carriers. As the light induced carriers reach the rectifying contact and raise the carrier concentration, the voltage across the contact decreases due to the dependence of the voltage on carrier concentration. This induces a transient negative resistance if the transit time of carriers from the illuminated section of the crystal is relatively long --Abstract, page ii