Electronic processes in double-barrier resonant-tunneling structures studied by photoluminescence spectroscopy in zero and finite magnetic fields

Clear evidence for space-charge buildup and the occurrence of sequential tunneling processes, in GaAs-${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Al}}_{\mathit{x}}$As double-barrier resonant-tunneling structures, is obtained from photoluminescence investigations in zero and finite magnetic fields. The charge densities in the quantum-well regions are determined from zero-field line-shape fits and the study of Landau-level intensities as a function of magnetic field. The occurrence of sequential tunneling in structures with two quasiconfined electron subbands is demonstrated from the spectroscopic observation of large charge densities in the lower subband, when the structures are biased for tunneling into the upper electronic level. The temperature of the electronic charge which builds up in the quantum wells at the two resonances is determined from the line-shape-fitting procedures.