Tunneling measurement of the density of states of a superlattice

We have studied the current-voltage characteristics of GaAs/AlGaAs samples consisting of an electron injector, a wide AlGaAs tunnel barrier, and a strongly coupled superlattice. The bias determines the energy of electrons injected into the superlattice, and the resulting tunnel current shows pronounced structure associated with minibands and band gaps. The position of the bands is in quantitative agreement with theory, and we resolve minibands with energies both below and above the AlGaAs conduction-band offset.