A current-controlled negative-resistance effect in indium antimonide

A thin wafer of P-InSb exhibits a current-controlled negative resistance between nonsymmetrical ohmic contacts on opposite sides of the wafer. The small contact on one side of the wafer is made positive relative to the large contact on the other side. Most effective samples had small contact diameters one to four times the slab thickness. The negative resistance was present up to a temperature of 210°K for material having 2.5 × 10¹⁴/cm³acceptor concentration at 77°K. A magnetic field perpendicular to the current flow direction reduced the value of the maximum negative resistance and extended the range of bias current yielding negative resistance. Samples under 0.005 inch thick yielded negative resistance when operated continuously, for the doping of 2.5 × 10¹⁴/cm³, but thicker samples yielded negative resistance only in lower duty cycle operation. Microwave radiation lines presumably at harmonics of oscillation in the bias circuit were measured. Finally, a proposed mechanism, dependent on impact ionization, is used to predict operation to a transit-time limited frequency of, say, 8000 Mc/s for a sample whose thickness is 0.0025 inch.