Unoccupied atomic-like states of gaas

The excitation spectrum of GaAs has been studied by reflection electron energy loss spectroscopy. In addition to dominant collective excitations, a series of single-electron transitions of a core Ga $3d$ electron to previously unknown unoccupied states located above the Fermi level by $1.25$, $3.7$, and $6.8$ eV have been detected in the spectrum. It has been shown that the detected states appear near the ion core of Ga because of an increase in its effective charge at excitation. Since the detected electronic levels are equidistant, they can be described by a subnanometer spherical quantum dot model. It has been shown that one of the decay channels of the detected states involves the emission of ultraviolet radiation.