OBSERVATION OF MULTISTATE NEGATIVE DIFFERENTIAL CONDUCTIVITY IN PERIODIC DELTA-DOPED SUPERLATTICE

A novel multistate S-shaped negative differential conductivity (NDC) delta-doped superlattice structure with long period (Z(p) = 600 angstrom) is observed and investigated. The multi-state NDC originates from a sequential sub-avalanche multiplication in the superlattice periods. Three different superlattices, i.e. one-period, three-period, and nine-period delta-(n+)-i-delta-(p+)-i delta-doped superlattices, were used. A different number of S-shaped NDCs are exhibited in each superlattice. An interesting hysteresis phenomenon was also apparent in the nine-period superlattice structure. It was attributed to the existence of heavy 'trapped' holes.