Antiferromagnetic coupling in CdSe/ZnMnSe quantum dot structures

Spin polarization of nonmagnetic CdSe quantum dots (QDs) coupled to adjacent ZnMnSe diluted magnetic semiconductor (DMS) is investigated by CW and time-resolved magneto-optical spectroscopy under tunable laser excitation. Efficient enhancement in the degree of σ− circular polarization of photoluminescence from the CdSe QDs is observed under optical excitation at the σ+-active exciton state of the DMS. The fact that the enhancement persists much longer than the exciton lifetime of the DMS rules out a role of the DMS excitons. A possible explanation is discussed in terms of antiferromagnetic coupling between the excitons in QDs and aligned Mn ions in DMS.funding agencies|Swedish Research Council|621-2007-4568621-2011-42542008-6582|Swedish Foundation for International Cooperation in Research and Higher Education (STINT)||Japan Society for the Promotion of Science||</p

Identification of point defects in Ga(Al)NAs alloys

By employing the optically detected magnetic resonance (ODMR) technique, two different Ga(ind i) defects, namely Ga(ind i)-A and Ga(ind i)-B, are found and identified in the investigated Ga(Al)NAs epilayers grown on GaAs substrates by molecular-beam epitaxy (MBE). This finding shows that Ga interstitials are common intrinsic defects in various dilute nitrides. In addition to the Ga(ind i)-related defects, "middle line" ODMR signals were observed at around g=2 and are suggested to arise from superposition of a defect with a single ODMR line and a defect with an unresolved HF structure. All defects studied are shown to act as non-radiative recombination centers, and are therefore harmful to performance of potential light-emitting devices based on the alloys

Room temperature spin filtering effect in GaNAs: Role of hydrogen

Effects of hydrogen on the recently discovered defect-engineered spin filtering in GaNAs are investigated by optical spin orientation and optically detected magnetic resonance. Post-growth hydrogen treatments are shown to lead to nearly complete quenching of the room-temperature spin-filtering effect in both GaNAs epilayers and GaNAs/GaAs multiple quantum wells, accompanied by a reduction in concentrations of Gai interstitial defects. Our finding provides strong evidence for efficient hydrogen passivation of these spin-filtering defects, likely via formation of complexes between Gai defects and hydrogen, as being responsible for the observed strong suppression of the spin-filtering effect after the hydrogen treatments. © 2011 American Institute of Physics

Effect of postgrowth hydrogen treatment on defects in GaNP

Effect of postgrowth hydrogen treatment on defects and their role in carrier recombination in GaNP alloys is examined by photoluminescence (PL) and optically detected magnetic resonance. We present direct experimental evidence for effective activation of several defects by low-energy subthreshold hydrogen treatment (<= 100 eV H ions). Among them, two defect complexes are identified to contain a Ga interstitial. Possible mechanisms for the H-induced defect activation and creation are discussed. Carrier recombination via these defects is shown to efficiently compete with the near band-edge PL, explaining the observed degraded optical quality of the alloys after the H treatment. (C) 2011 American Institute of Physics. [doi:10.1063/1.3576920