Magneto-optical properties in IV-VI lead-salt semimagnetic nanocrystals
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NANO REVIEW
Open Access
Magneto-optical properties in IV-VI lead-salt semimagnetic nanocrystals Silvio J Prado1 , Leonardo Villegas-Lelovsky2* , Augusto M Alcalde2 , Victor Lopez-Richard3 and Gilmar E Marques3
Abstract We present a systematic study of lead-salt nanocrystals (NCs) doped with Mn. We have developed a theoretical simulation of electronic and magneto-optical properties by using a multi-band calculation including intrinsic anisotropies and magnetic field effects in the diluted magnetic semiconductor regime. Theoretical findings regarding both broken symmetry and critical phenomena were studied by contrasting two different host materials (PbSe and PbTe) and changing the confinement geometry, dot size, and magnetic doping concentration. We also pointed out the relevance of optical absorption spectra modulated by the magnetic field that characterizes these NCs. Keywords: Nanocrystals, Quantum dots, DMS, II-VI semiconductors, Lead salts, Magneto-optical properties
Review Recently, the successful fabrication of IV-VI nanocrystals doped with Mn has shown possible effective tuning of the ˚ up emission energy from infrared (dot radius 200 A) ˚ regions [1]. The to near-ultraviolet (dot radius 20 A) IV-VI semiconductors, such as PbSe nanocrystals (NCs), provide access to the limit of strong quantum confinement where, besides the changes induced by very small dot size, the direct narrow band-gap that can also be engineered by the gradual addition of dilute amounts of magnetic Mn ions to the dot structure. The members of the lead-salt family, such as PbSe and PbTe, have rock-salt crystalline structure with a direct bandgap in the L-point and the energy branches are four-fold degenerate. The bottom of the conduction band has L− 6 symmetry with the top of the valence band displaying L+ 6 symmetry of the double group D3 . This corresponds to the opposite situation observed in III-V or II-VI zinc blend materials, since here the valence band-edge Bloch function displays s-like symmetry whereas the conduction band-edge Bloch function has pz -like symmetries, where z denotes the 111 direction of the cubic lattice [2].
*Correspondence: [email protected] 2 Instituto de Fisica, Universidade Federal de Uberlandia, Uberlandia, Minas Gerais 38.400-902, Brasil Full list of author information is available at the end of the article
In this letter, we contrast quantum dot electronic properties of two IV-VI semiconductor materials by modifying the quantum confinement from spherical to semispherical and varying the diluted concentration of incorporated Mn2+ ions. The electronic, magnetic, and optical properties are studied as a function of Mn content for varying temperature. The total Hamiltonian of the system is H = Hkp + V + Hx where Hkp is the hyperbolic or Kane-Dimmock [3] k · p Hamiltonian model for IV-VI semiconductors, V is a hard wall confinement potential and Hx is the exchange interaction between Mn2+ ions and conduction band (valence band) spins. Here, Hkp was slightly modified to explore spherical symmetries of the confinem
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