Energy relaxations in hot electrons emitted by a quantum dot

Mesoscopic quantum dots (QDs) are commonly used as reliable sources of hot electrons. However, we have found that two-dimensional hot electrons with excitations ≤1.5 meV may lose up to ≈ 55% of its energy immediately following their emission from a QD. The unexpected energy relaxation was identified from transverse magnetic focusing, where the focusing spectra were obtained from QD and quantum point contact (QPC) emitter experiments. Unlike its QPC counterparts, the dynamics of QD emissions significantly differed from Fermi gas predictions. With increasing hot electron energy, the focusing peaks appeared at relatively lower magnetic fields with excessive broadening. The phenomenon was modeled as an electrostatic interaction between the QD and the electron reservoir through which a hot electron may transfer its energy back to its emitter QD. Model simulations predicted a set of focusing spectra with the key features observed in experiment, implying that a QD may not be adequate as a monoenergetic source for electrons with energies beyond the QD excitation levels.