Resonant tunneling is investigated in GaAs/${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As double-barrier heterostructures grown by metal-organic chemical-vapor deposition (MOCVD) in the [100] direction. The quantum-well energy levels which produce the negative differential resistances observed in the experimental current-voltage characteristics are identified by calculating the energy-band diagrams of the structures. Energy-band profiles are essential to properly account for the voltage drops in all the layers, and to correlate unambiguously the experimental negative differential resistances with the resonances in the well. In samples having pure AlAs barrier layers, the peaks in current correspond to resonant states confined in the GaAs well by the AlAs X-point potential-energy barriers in addition to the AlAs Γ-point barriers. The quasibound X states are associated with the large longitudinal effective mass in AlAs corresponding to the direction perpendicular to the heterojunction interfaces. The relative intensity of Γ- and X-point tunneling is found to differ from sample to sample. In some structures, it also depends on the sign of the applied bias. Such effects may be related to the quality of the materials and the heterojunction interfaces.

• Received 30 November 1987

DOI:https://doi.org/10.1103/PhysRevB.37.8754