The lead chalcogenides PbX (X = S, Se, and Te), in particular nanocrystals and quantum dots built by their heterostructures, are a highly attractive class of materials in semiconductor research. Such structures are potential candidates for midinfrared optoelectronic devices. For instance, midinfraredlaser emission from selforganized PbSe quantum dots in aPbSe/ Pb_{1-x}Eu_{x}Te quantum dot superlattice has been realized [1].In this work, we focus on a similar system, i.e., the PbSe/ Pb_{1-x}Eu_{x}Teheterostructure, which is also a candidate for technological application. Concerning the experimental realization, such heterostructures are grown by molecular beam epitaxy. Due to the lattice mismatch between the subtrates PbSe and Pb_{1-x}Eu_{x}Te, strain induced changes of the energy gap of PbSe arise. This dependence of the energy gap on the Eu doping concentration x can be calculated using the deformation potentials (DP), as long as the strain is in the linear regime. The experimental determination of the deformation potentials for such systems is a difficult task and thus the measured values show large variations [2,3]. For this reason, the ab initio calculation of the DPs is of particular interest. This has motivated us to thoroughly investigate(i) the structural, elastic, and electronic properties including the effective charge carrier masses of the bulk lead chalcogenides from first principles[4],(ii) the EuSe band structure,(iii) the uniaxial as well as the dilatational potential of PbSe in the PbSe/ Pb_{1-x}Eu_{x}Te heterostructure, and (iv) the dependence of the energy gap of Pb_{1-x}Eu_{x}Te on the Eu doping concentration x. Experimentally, a doping concentration of up to 10% Eu in Pb_{1-x}Eu_{x}Te is used in order to increase the energy gap of the alloy. Despite this significant Eu doping, a strong influence on the crystal volume has not been obtained [5]. Regarding to (ii), the properdescription of the 4f states in Eu that cause a net magnetic moment is of particular interest.The ab initio calculations have been primarily carried out within standard density functional theory (DFT) utilizing local and semilocal exchange correlation functionals such as the local density approximation (LDA) and generalized gradient approximation (GGA). For further improvement of the calculated results, the hybrid functional HSE03, which has proven to yield superior energetics and band gaps for a wide class of materials [6], has been employed. All calculations have been performed with the projector augmented wave method as implemented in the VASP code. For the band structure calculations of EuSe with occupied 4f spin-up and unoccupied 4f spin-down states the GGA plus Hubbard U has been used and compared to the results obtained with the HSE03 functional.[1] G. Springholz, T. Schwarzl, W. Heiss, G. Bauer, M. Aigle, H. Pascher, and I. Vavra, Appl. Phys. Lett. 79, 1225 (2001).[2] I.I. Zasavitskii, E. A. de Andrada e Silva, E. Abramof, and P. J. McCann, Phys. Rev. B 70, 115302 (2004).[3] M. Simma, D. Lugovyy, T. Fromherz, A. Raab, G. Springholz, and G. Bauer, Physica E 32, 123 (2006).[4] K. Hummer, A. Grüneis, and G. Kresse, Phys. Rev. B., submitted (2007).[5] G. Springholz, private communication.[6] J. Paier, M. Marsman, K. Hummer, G. Kresse, I. C. Gerber, and J. G. Ángyán, J. Chem. Phys. 124, 154709 (2006), J. Chem. Phys. 125, 249901 (2006).
| Period | 14 May 2008 |
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| Event title | 8th International Conference on Mid-Infrared Optoelectronics: Materials and Devices |
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| Event type | Conference |
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| Location | Bad Ischl, AustriaShow on map |
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