Defects Introduced in Neutron-Irradiated Esaki Diodes

Ge and Si Esaki diodes have been subjected to reactor neutron irradiation at 90°K. Ge diodes show no structure in the radiation-induced excess current during irradiation but develop a hump at 0.30-V bias upon anneal to above 250°K, when observed at 77°K. In accordance with a model interpreting hump structure as being due to direct tunneling involving narrow defect levels deep in the forbidden band, the lack of structure in the ``as-irradiated'' Ge diodes is interpreted as being associated with a continuum of levels arising from large clusters of defects. The growth of the hump (corresponding to an energy level at Ev+0.31 eV) during anneal is associated with the breakup of large clusters into smaller defects, giving rise to a discrete energy level. Most of the continuum of added excess current (at bias values away from the hump), as well as the hump current, anneals out below 450°K. Anneal of the continuum agrees closely with recovery of length change in deuteron bombarded Ge which has also been interpreted as being due to the breakup of clustered defects. Si diodes show hump structure at 0.3 and 0.6 V after irradiation and anneal to 195°K, upon observation at 77°K, and at 0.9 V in the course of further anneal. These humps are associated with energy levels at approximately Ev+0.35, Ec −0.45, and Ec −0.15 eV, respectively. Hump structure and annealing behavior are quite similar to that observed after low temperature electron irradiation, except that the structure is somewhat less distinct after neutron bombardment. According to the interpretation given the Ge results, this implies that large clustered defects in neutron irradiated Si must have already partially annealed below 195°K or are relatively less numerous or less evident in their effects than in Ge.