Thermal instability in very small p-n junctions

Thermally induced second breakdown is studied in very small 6- to 10-volt silicon diodes having uniform breakdown. The formation of a small high-current density region is observed optically at the onset of thermal breakdown. Incremental resistance measurements can be used to determine nondestructively the threshold current for thermal breakdown. The threshold temperature for thermal breakdown is measured using the avalanche voltage temperature coefficient. The voltage drop associated with thermal breakdown is shown to be due to a sudden change in active area of the junction rather than to melting of the crystal.