Regensburg 2004 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 35: Symposium Ferromagnetische Halbleiter

HL 35.2: Vortrag

Donnerstag, 11. März 2004, 10:45–11:15, H15

Carrier induced ferromagnetism in p type doped II-VI heterostructures — •David Ferrand — CEA-CNRS-UJF Joint Group, Laboratoire de Spectrometrie Physique, BP 87 38402 Saint Martin d’Heres, France

Carrier-induced ferromagnetism in diluted magnetic semiconductors (D.M.S) has been reported in IV-VI bulk alloys, III-V epilayers and in II-VI heterostructures. In comparison to III-V, the Curie temperatures are dramatically lower in II-VI DMS, but II-VI compounds are ideal materials for fundamental studies, in which localized spins and holes can be introduced and controlled independently and where dimensionality effects can be examined in modulation doped heterostructures. We will present here an overview of our experimental studies, we have done on degenerate Zn_(1−x)Mn_xTe thick layers and modulation-doped Cd_(1−x)Mn_xTe quantum wells. Zn_(1−x)Mn_xTe with Mn content up to several percents can be easily doped p-type using a nitrogen cell up to 10²⁰cm⁻³, two orders of magnitude larger than the density for metal-insulator transition. While the usual antiferromagnetic behavior is observed on the susceptibility of undoped layers, we observed (SQUID and anomalous Hall effect) positive Curie-Weiss temperatures between 1.5 and 3K and characteristic ferromagnetic hysteresis cycles, for layers with hole densities above a few 10¹⁹ cm⁻³. In the case of Cd_(1−x)Mn_xTe quantum wells, the magnetic signal appears to be too small to be measured directly and is determined indirectly from magneto-optical spectroscopy. Curie temperatures up to 3K have been observed for single quantum wells with Mn content up to 4% and with hole densities between few 10¹⁰ and 6·10¹¹ cm⁻². In both cases, the experimental Curie temperatures are in good agreement with mean field predictions. Finally, we will conclude this presentation by showing our recent work on MBE growth and characterization of high gap diluted magnetic semiconductor epilayers GaMnN and ZnCoO.