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Physical Society Colloquium
their spatial distribution and dynamics Yoshiro Hirayama NTT Basic Research Laboratories Understanding the fundamental features of electrons, such as spatial distributions and dynamics, in semiconductor quantum dots is both interesting and important. In typical semiconductors, seeing the local-density-of-states in conductive electrons from the surface is very difficult. However, the unique feature of the InAs (111)A heterostructure makes it possible. Two-dimensional electrons accumulate near the surface and a tetrahedral defect operates as a quantum dot. By using scanning-tunneling-microscope (STM) measurements at a low temperature, we have successfully imaged the local-density-of-states in zero-dimensional electrons that are confined in the quantum dots. The electron dynamics are also important characteristics. We have studied electron relaxation from excited to ground levels in quantum dots by using sophisticated pulse technique. We used lateral and vertical GaAs (or InGaAs) quantum dots for this relaxation experiment. The obtained results clearly confirm an extremely long relaxation time for the spin-flip transitions. This result indicates a separation of spin and orbital degrees of freedom in semiconductor quantum dots. It encourages the use of electron-spin in quantum dots to spintronics and coherent spin-control devices.
Friday, May 17th 2002, 15:30 |