First principles investigations of Fe~(3+) impurity and Fe~(3+) + V_(cd)~+ complex in strongly confined CdSe quantum dot

摘要

Solitary dopant or defect in a semiconductor is the basis of the emerging field of optoelectronics known as solotronics. It has been shown that the spin of a single magnetic ion impurity can be manipulated optically. Among the magnetic ions, Fe~(3+) has been proposed as a primary candidate for the design of quantum dots (QDs) for solotronics because of its zero nuclear spin in contrast to Mn~(2+) and larger magnetic moment compared to Fe~(2+). In this work, we performed density function theory calculations to determine optimal parameters for the colloidal synthesis of single Fe_(Cd)~(3+) over Fe_(Cd)~(2+) in CdSe of 1 nm in radius. We also investigated Fe~(3+) plus Cd vacancy complex (Fe_(Cd)~(3+) + V_(Cd)~- ). Transition energy level calculations show Fe_(Cd)~(3+) to be a deep-level donor and V_(Cd)~- to be a shallow acceptor. Charge difference plots show that the charge of the ionized electron is localized around Fe_(Cd)~(3+) . Tetrahedral symmetry is retained at the Fe_(Cd)~(3+) site. The magnetic moment of Fe~(3+) is almost the same in the core and at the surface and is equal to ～4.27 μ_B for passivated QD. The large moment can be manipulated for spin control in conjunction with unoccupied vacancy states of the triplet t_2 level of the shallow V_(Cd) acceptor to create a hole spin current in a lithographically patterned surface.