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The critical current at which pinching occurs in indium antimonide has been measured by three independent methods: (a) by noting the current at which the pinched current-voltage characteristic deviates from the unpinched characteristic that is obtained in the presence of a longitudinal magnetic field H, using crystals of sufficiently high resistance for the avalanche breakdown current to be considerable, before pinching sets in, as the electric field is increased; (b) by noting the current at which the magnetoresistance, as a function of H, shows a change in its behavior; and (c) from a study of the critical current as a function of H. The three methods lead to a value for the critical pinching current of 4-5 amp. This current is the same for both single-crystal and polycrystalline samples, and is insensitive to small changes in the donor concentration or cross-sectional area of the crystal. The value of the critical current leads to a mean carrier temperature of 0.04 ev in avalanche breakdown. An irregular form of noise is observed when the crystal is operated in the transition region between the pinched and unpinched conditions, and it is thought that this noise is caused by pinching-unpinching instabilities.

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