Mode structure and drift velocity thresholds for instability have been investigated for the type-I superlattice, and a new current-induced mode is found to exist for high drifts. Simple separation of the single-layer physics and superlattice geometry has been achieved, leading to an analytical expression for the Giuliani-Quinn mode and universality relations for the instability threshold curves of the new mode.

• Received 11 July 1988

DOI:https://doi.org/10.1103/PhysRevB.38.10051