Optical properties of GaN-based diluted magnetic semiconductor GaCrN were studied. The GaCrN layers were grown by electron-cyclotron-resonance plasma-assisted molecular-beam epitaxy. They exhibited ferromagnetic behavior at room temperature and strong photoluminescence (PL) emission at 3.29 eV (10 K). The PL emission peak energy of the GaCrN decreases with increasing temperature in accordance with the Varshini formula similar to the GaN excitonic transition peak. The 3.29 eV PL emission was assigned to be a band-to-band transition in GaCrN from the temperature- and the excitation-power-density dependences of the PL.

Local structure around gadolinium atoms in Ga1−xGdxN (x = 0.06) was studied by extended X-ray absorption fine structure measurement using Gd LIII-edge. Majority of Gd atoms are found to be substitutionally incorporated into the Ga sites of wurzite structure of GaN and GaGdN layer is formed. Bond lengths of the 1st nearest-neighbor and the 2nd nearest-neighbor shells of GaGdN layer are largely elongated due to the incorporation of Gd atoms. This indicates that although wurtite structure of GaN is maintained, lattice structure of GaGdN layer is under strong distortion.

Magnetic properties of molecular-beam epitaxy grown Eu-doped GaN are studied. At high temperatures, clear hysteresis and clear saturation indicating the existence of a ferromagnetic-like phase are observed in the magnetization versus magnetic curves, while at low temperatures gradually saturating nonlinear field dependence of the magnetization is also observed. The easy-axis for the ferromagnetization is perpendicular to the sample plane. A theoretical model is proposed to account for the experimental results, assuming that a molecular field is acting on Eu ions via the spin-polarized valence-band of GaN. The experimental results are accounted for by assuming the coexistence of Eu2+ ions and Eu3+ ions interacting through the Ruderman-Kittel-Kasuya-Yoshida-type interaction.

III-V-ba,sed magnetic semiconductors are new functional materials that are expected to lead to the introduction of spin degree-of-freedom for semiconductor devices. This paper describes (1) InMnAsSb/InSb magnetic semiconductor heterostructures and mid-infrared light-induced ferromagnetism, (2) GaN-based magnetic semiconductor GaCrN and high temperature (> 400 K) ferromagnetism and photoluminescence emission, and (3) Mn-including InAs quantum dot structures.

Magnetic properties of the rare-earth-doped III-nitride semiconductor Ga1-xEuxN (x = 0.02) were studied together with X-ray absorption fine structure (XAFS) measurements. Experimental results show that the GaEuN layer is not only paramagnetic originating from the non-magnetic F-7(0) ground level of trivalent Eu ions, but exhibits also ferromagnetic-like behaviour with easy axis perpendicular to the sample plane. This ferromagnetic component seen also at 300 K seems to be related to divalent Eu ions. The observed magnetic behaviour was also studied theoretically, by introducing a c-axis oriented molecular-field term that acts via the spin-polarized valence band of GaN. This result suggests that Eu ions interact with other Eu ions through the RKKY-type interaction. (C) 2003 WILEYNCH Verlag GmbH & Co. KGaA, Weinheim.

II-V-based magnetic semiconductors are gathering great interest because of their potential utility as new functional materials that are expected to lead to the introduction of spin degree-of-freedom for semiconductor devices. New magnetic semiconductor heterostructure, InMnAsSb/InSb, was proposed and grown by low temperature molecular beam epitaxy (MBE). Mid-infrared (2-6 μm) light-induced ferromagnetism was observed at temperatures lower than 40-50K and this light-induced magnetization remained even after the stop of light irradiation. Observed characteristics are applicable to the mid-infrared sensor/memory devices. New magnetic semiconductor GaCrN layers were grown by electron-cyclotron-resonance (ECR) plasma-assisted MBE and the ferromagnetic characteristics were observed at 7-400K. Clear hysteresis and clear saturation were observed in the magnetization versus magnetic field (M-H) curves at all measuring temperatures. We also observed the photoluminescence (PL) emission from GaCrN layers. Applications to the novel devices controlling charges (electrons and holes), spins and photons are expected.

New diluted-magnetic heterostructure, InMnAsSb/InSb, was proposed and grown by low temperature molecular beam epitaxy. Raman scattering measurement showed the better crystalline quality of InMnAsSb grown at 250 degreesC than that grown at 280 degreesC. Phase separation was observed in InMnAsSb layer grown on GaAs substrates and was not observed in InMnAsSb layer on InAs substrates. By the irradiation of light longer than 2 mum at low temperatures, the magnetization of InMnAsSb/InSb heterostructure grown on GaAs substrates showed no change, while that of InMnAsSb/InSb heterostructure grown on InAs substrates was increased and this light-induced magnetization remained even after the stop of light irradiation. On the other hand, the InMnAsSb/InAsSb/InSb heterostructure showed light-induced magnetization, but it recovered to initial value after the stop of light irradiation.