Mesoscopic electron transport in semiconductor nanostructures

This thesis presents experiments investigating mesoscopic electron transport in semiconductor nanostructures. The devices studied were fabricated in GaAs/AlGaAs heterostructures containing two-dimensional electron gases. The first experiment studies the breakdown of charge quantization in a quantum dot functioning as a single-electron box. The charge in the box is measured directly using a second, capacitively coupled quantum dot functioning as a single-electron transistor electrometer. The electrometer is demonstrated to be superior to conductance measurements for studying charge quantization in quantum dots, and is used to directly measure the breakdown of charge quantization in the box as the box-to-lead tunnel-coupling is increased. Charge quantization is shown to be destroyed at a tunnel-coupling of 2e2/h in agreement with theory.; Two other experiments on quantum dots are also presented. The first uses Coulomb blockade spectroscopy to study manifestations of spin in the addition spectrum of a small quantum dot. The motion of Coulomb blockade peaks is studied in a parallel magnetic field. The peak motion at low field is interpreted as due to the electron spin and is consistent with that expected from Zeeman coupling, but at higher field orbital effects are found to be important. The final quantum dot experiment studies the magnetic field behavior of two quantum dots in an artifical molecule. Mesoscopic fluctuations are observed in the double dot ground state energy and other properties which can be explained by the interference of electron wavefunctions on the dots.; Finally, experiments on an electron resonator are presented. The resonator is an open structure in which the effects of quantum interference of electrons are dramatically apparent. Conductance peaks in transport measurements are observed which are explained by the constructive interference of electron waves with a period of a Fermi wavelength. The peak positions are found to shift in a perpendicular magnetic field. These shifts are explained by the combined effects of electron trajectory bending and the Aharanov-Bohm phase shift.