ELECTRON-SPECTROSCOPIC STUDY OF VERTICAL IN1-XGAXAS QUANTUM DOTS

We present the results of a magnetotransport study of vertical In1-xGa xAs 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 mag netic field perpendicular to the current. In perpendicular field, a su ppression of the current plateaus is observed that is not present in p arallel field. We also observe fine structure on the current plateaus and study its magnetic field dependence. We observe that the fine stru cture moves systematically in voltage with changing magnetic field, in both the perpendicular and parallel field orientations, while the pla teau edges only exhibit a diamagnetic shift in parallel field. The cur rent plateau step edge exhibits the expected Fermi-level broadening wi th 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 o f this fine structure to the dopant-induced discreteness of the electr onic density of states in the emitter.