Tunneling Phenomena in GaAs/AlGaAs Double Quantum Well Structures

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1.The mechanism and the speed of tunneling in double quantum well strucutres(DQW), which have two GaAs quantum wells with different widths and separated by a thin AlGaAs potential barrier, have been investigated. The samples were made with MBE and MOVPE. The electrical as well as the opotical properties of DQW have been studied.2.Applying an electric field parallel to the heterointerface, electrons in the wide well are accelerated to become hot. The current-voltage characteristics exhibit a kink due to the real space transfer of electrons into the narrow well. It is found that the tunneling is due to the LO phonon-assisted indirect process.3.By an electric field perpendicular to the heterointerface, the difference energy between the two quantized levels in DQW was changed, and the tunneling time was measured by femtosecond spectroscopy. It was found that the tunneling time is a strong function of the electric field, and that the tunneling is due to LO phonon assisted at the off resonance condition.4.The effect of the fabrication process on the tunneling is investigated by making quasi-one dimensional structures. It was found that the tunneling time as well as the energy relaxation time of electrons are significantly reduced. The scattering due to the surface roughness does give the predominant mechanism in the tunneling phenomena in small structures.