Two-step decoupling of excitonic states in a biperiodic GaAs/AlAs short period superlattice under electric fields

By low temperature photocurrent spectroscopy, we have investigated electric field dependence of excitonic states in a biperiodic GaAs/AlAs short-period superlattice which consists of a 20-period of GaAs-well(L_Z) / AlAs-barrier1(L_B¹) / GaAs-well(L_Z) / AlAs-barrier2(L_B²) (= 3.2nm / 0.45nm / 3.2nm / 0.9nm). Evidence is given for a two-step decoupling mechanism at low (< 10⁵V/cm) and high (> 10⁵V/cm) field regimes, which is derived from the successive decoupling of the superlattice potential coupling and of the symmetric two-well-coupling through the thinner barrier.