1. AN ELECTRICAL DEVICE COMPRISING A CARRIER-DENSITY, ELECTRIC-FIELD-QUENCHABLE, PHOTOCONDUCTIVE BODY HAVING THE PROPERTY THAT ANY FREE CHARGE CARRIER CONCENTRATION WITHIN IT GREATER THAN THAT CORRESPONDING TO THERMAL EQUILIBRIUM IS REDUCED IN THE PRESENCE OF AN ELECTRIC FIELD, ELECTRODE MEANS COUPLED TO THE BODY INCLUDING A VOLTAGE SOURCE FOR CAUSING TO PASS THROUGH THE BODY BETWEEN THE ELECTRODE MEANS A CURRENT WHOSE MAGNITUDE DEPENDS UPON THE FREE CHARGE CARRIER CONCENTRATION WITHIN THE BODY, WHICH PRODUCE A CURRENT-VOLTAGE CHARACTERISTIC OF THE DEVICE, MEANS FOR ESTABLISHING WITHIN THE BODY A FREE CHARGE CARRIER CONCENTRATION GREATER THAN THAT CORRESPONDING TO THERMAL EQUALIBRIUM TO INCREASE THE CURRENT THROUGH THE BODY BETWEEN THE ELECTRODE MEANS, AND MEANS FOR ESTABLISHING AN ELECTRIC FIELD WITHIN THE BODY THAT REDUCES THE CONCENTRATION OF FREE CHARGE CARRIERS AND THUS THE CURRENT FLOW BETWEEN THE ELECTRODE MEANS, WHEREBY THE CURRENT-VOLTAGE CHARACTERISTIC OF THE DEVICE EXHIBITS A REGION OF NEGATIVE SLOPE.