Direct Observation of Superlattice Formation in a Semiconductor Heterostructure

We demonstrate, via low-temperature optical-absorption measurements on ultrathin, coupled potential wells in molecular-beam-grown ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$-GaAs heterostructures, the evolution of resonantly split discrete well states into the lowest band of a one-dimensional superlattice. Both electron and hole superlattices appear to be practical.