Electron-spectroscopic study of verticalIn1−xGaxAs quantum dots

We present the results of a magnetotransport study of vertical ${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ga}}_{\mathit{x}}$As quantum dots. We observe a series of current plateaus, due to the quantum dot eigenstates, that exhibit a purely diamagnetic response in magnetic field parallel to the current, and no shift in energy in magnetic field perpendicular to the current. In perpendicular field, a suppression of the current plateaus is observed that is not present in parallel field. We also observe fine structure on the current plateaus and study its magnetic field dependence. We observe that the fine structure moves systematically in voltage with changing magnetic field, in both the perpendicular and parallel field orientations, while the plateau edges only exhibit a diamagnetic shift in parallel field. The current plateau step edge exhibits the expected Fermi-level broadening with temperature whereas the fine structure is observed to be relatively temperature insensitive. This is indicative of tunneling from states in the emitter below the Fermi level. Additionally, thermal activation of subthreshold fine structure is observed. We attribute the origin of this fine structure to the dopant-induced discreteness of the electronic density of states in the emitter. © 1996 The American Physical Society.