Tunneling Phenomena in GaAs/AlGaAs Double Quantum Well Structures

1.本文研究了由薄AlGaAs势垒隔开的两个不同宽度的GaAs量子威尔斯阱构成的双量子阱结构的隧穿机制和隧穿速度。用MBE和MOVPE制备样品。研究了DQW的电学和光学性质。2.施加一个平行于异质界面的电场，使宽阱中的电子加速变热。由于电子进入窄阱的真实的空间转移，电流-电压特性表现出扭结。发现隧穿是由于LO声子辅助的间接过程。3.在垂直于异质界面的电场作用下，改变了DQW中两个量子化能级之间的能量差，并利用飞秒光谱测量了隧穿时间。发现隧穿时间是电场的强函数，隧穿是由于在非共振条件下LO声子的辅助作用。4.通过制作准一维结构，研究了制作工艺对隧穿的影响。结果发现，隧穿时间以及电子的能量弛豫时间显着减少。由于表面粗糙度的散射在小结构中的隧穿现象中给出了主要机制。

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.