SPIN SPLITTING OF SINGLE 0D IMPURITY STATES IN SEMICONDUCTOR HETEROSTRUCTURE QUANTUM WELLS

Zeeman splitting of the ground state of single impurities in the quantum well of a resonant tunneling heterostructure is reported. We determine the absolute magnitude of the effective magnetic spin splitting factor g p for a single impurity in a 44 AA l 0.27Ga0.73AsyGaAsyAl0.27Ga0.73As quantum well to be 0.28 6 0.02. This system also allows for independent measurement of the electron tunneling rates through the two potential barriers and estimation of the occupation probability of the impurity state in the quantum well. The experimental realization of granular electronic systems, such as low dimensional semiconductor and ultrasmall metallic systems, has focused attention on the basic physical properties of discrete systems. Especially intriguing are the semiconductor quantum dot [1 ‐ 5] and the physically similar localized impurity state tunneling systems [6 ‐10]. The latter provides a unique laboratory for the study of a single impurity. We present here the first observation of Zeeman spin splitting of a single semiconductor impurity, studied by tunneling transport. The measured g p factor provides an important test of the band theory of confined semiconductor systems, and our method is particularly important for well widths less than 50 A where other methods are less precise [11‐ 13]. Isolated donor impurities in the quantum well regions of large area resonant tunneling structures form localized (,100 A) hydrogenic states bound to the quantum eigenstates. Figure 1 illustrates a band diagram of the structure used in this study with one impurity state in the well schematically noted. In an applied bias when the impurity state aligns with the emitter Fermi level, the current exhibits a steplike increase. In general, there may be multiple impurities giving rise to multiple, overlapping steps in the current-voltage [IsV d] characteristics. An appropriately dilute, unintentional doping concentration gives rise to isolated, uncorrelated impurities, allowing measurement of a single one. In a magnetic field the spin degeneracy of the impurity ground state is broken, resulting in a splitting of the current step in the IsV d characteristics. The magnitude of the spin g p factor can be determined from the voltage difference between the two fragments of the spin-split step. The current magnitudes of the two fragments enable us, for the first time, to independently determine the electron tunneling rates through the two potential barriers in a sequential tunneling picture [4,14].