Dilute magnetic semiconductors (DMS), combining magnetic ordering with semiconductor properties, are considered key ingredients for the production of new devices using the electron spin in microelectronics applications. In DMS, the metal species (e.g., Mn) yields both localized magnetic moments and itinerant holes. Both are crucial for a ferromagnetic behaviour of the DMS, as the holes are thought to mediate the exchange interactions between magnetic moments. Recently, the effects of the introduction of atomic hydrogen in a Mn$_{(x)}$Ga$_{(1-x)}$As (x=0.037-0.051) DMS have been experimentally investigated.[3,4] Infrared measurements of hydrogenated (deuterated) Mn$_{(x)}$Ga$_{(1-x)}$As show As-H (As-D) local vibrational modes, characteristic for the complexes formed by hydrogen with group-II acceptors in GaAs. Magnetization measurements show that the as-grown Mn$_{(x)}$Ga$_{(1-x)}$As films are ferromagnetic whereas they become paramagnetic after hydrogenation. Moreover, electronic transport measurements indicate that the density of free holes is reduced by hydrogenation. In the present study, we have investigated the structural, vibrational, electronic and magnetic properties of complexes formed by H in the Mn$_{(x)}$Ga$_{(1-x)}$As (x=0.03) DMS by using Density-Functional Theory and the LDA+U method.[5] The results show that H forms a stable As-H(-Mn) complex where it binds to an As atom nearest neighboring the Mn atom and is located close to the center of the As-Mn bond. In this complex, the calculated As-H vibrational frequency agrees with the measured IR frequencies. The calculated magnetization for the Mn atom in the complex is equal to 5 (B, in agreement with the experiment. Moreover, an estimate of the position of the acceptor level induced by Mn in the GaAs energy gap shows that this level is removed from the gap when the As-H(-Mn) complex is formed. This leads to a full neutralization of the Mn acceptor, thus accounting for the observed evolution of the electronic and magnetic properties of the Mn$_{(x)}$Ga$_{(1-x)}$As DMS upon hydrogenation. The present results also indicate that electron correlation has crucial effects on the stability of the H complexes.
Hydrogen complexes in Mn(x)Ga(1-x)As dilute magnetic semiconductors
Filippone F;Amore Bonapasta A;
2005
Abstract
Dilute magnetic semiconductors (DMS), combining magnetic ordering with semiconductor properties, are considered key ingredients for the production of new devices using the electron spin in microelectronics applications. In DMS, the metal species (e.g., Mn) yields both localized magnetic moments and itinerant holes. Both are crucial for a ferromagnetic behaviour of the DMS, as the holes are thought to mediate the exchange interactions between magnetic moments. Recently, the effects of the introduction of atomic hydrogen in a Mn$_{(x)}$Ga$_{(1-x)}$As (x=0.037-0.051) DMS have been experimentally investigated.[3,4] Infrared measurements of hydrogenated (deuterated) Mn$_{(x)}$Ga$_{(1-x)}$As show As-H (As-D) local vibrational modes, characteristic for the complexes formed by hydrogen with group-II acceptors in GaAs. Magnetization measurements show that the as-grown Mn$_{(x)}$Ga$_{(1-x)}$As films are ferromagnetic whereas they become paramagnetic after hydrogenation. Moreover, electronic transport measurements indicate that the density of free holes is reduced by hydrogenation. In the present study, we have investigated the structural, vibrational, electronic and magnetic properties of complexes formed by H in the Mn$_{(x)}$Ga$_{(1-x)}$As (x=0.03) DMS by using Density-Functional Theory and the LDA+U method.[5] The results show that H forms a stable As-H(-Mn) complex where it binds to an As atom nearest neighboring the Mn atom and is located close to the center of the As-Mn bond. In this complex, the calculated As-H vibrational frequency agrees with the measured IR frequencies. The calculated magnetization for the Mn atom in the complex is equal to 5 (B, in agreement with the experiment. Moreover, an estimate of the position of the acceptor level induced by Mn in the GaAs energy gap shows that this level is removed from the gap when the As-H(-Mn) complex is formed. This leads to a full neutralization of the Mn acceptor, thus accounting for the observed evolution of the electronic and magnetic properties of the Mn$_{(x)}$Ga$_{(1-x)}$As DMS upon hydrogenation. The present results also indicate that electron correlation has crucial effects on the stability of the H complexes.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
