Low-temperature (77–300 K) current-voltage characteristics of 4H-SiC $p^+$–$p$–$n^+$ diodes: Effect of impurity breakdown in the $p$-type base

The effect of impurity breakdown on the low-temperature (77–300 K) current-voltage (I–V) characteristics of 4H-SiC diodes with a $p$-type base has been studied. Experimental samples were fabricated from CVD-grown (chemical vapor deposition) commercial $p^+$–$p$–$n^+$ 4H-SiC structures. A high electric field in the $p$-type base was created by applying a forward bias to the diodes. It was found that, at temperatures of 136, 89, and 81 K, the commonly observed “diode” portion of the I–V characteristics is followed by a portion in which the current grows more rapidly due to the impact ionization of frozen-out Al acceptor atoms in the ground (unexcited) state. At temperatures of 81 and 77 K, this portion is followed by one with a negative differential resistance due to the regenerative dynistor-like switching of the diode, caused by impact ionization of aluminum atoms in the excited state.