Study on photo-induced magnetic transition in II-VI diluted magnetic semiconductor quantum wells with a type band allignment

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1. Preparation of p-type ZnSe/BeMnTe quantum well structuresZnSe/N-doped BeMnTe quantum wells and N-doped BeMnTe thin films were grown on GaAs substrates by a molecular beam epitaxy method. The hole carrier density in the range of 10^<18>-10^<19> cm^<-3>, which corresponds to the carrier density necessary for carrier-induced ferrpmagnetism, was obtained at the temperatures between 2 and 300 K.2. Analysis of cross-sectional structure of ZnSe/BeTe quantum well interfacesCarrier lifetimes and overlapping of electron and hole wave functions strongly depend on the interfacial quality, because the recombination between electrons and holes takes place at the interfaces in the quantum wells with a type II band alignment. We investigated sharpness and alloy effects at the interfaces between ZnSe and BeTe layers in the multiple quantum wells using cross-sectional scanning tunneling microscopy and X-ray diffraction measurements. The filled- and empty-state images revealed that Zn-Te and Be-Se bon … More ds exist at the ZnSe/BeTe interface within the range of 2-4 monolayers along the growth direction. The transition layer between the ZnSe layer and the BeTe layer is composed of the BeZnSeTe quaternary alloy corresponding to (ZnTe)_<0.58>(BeSe)_<0.42>.3. Observation of anomalus Hall effects and ferromagnetic transitionWe measured anomalus Hall effects in N-doped Be_<1-x>Mn_xTe (x=0.05 and 0.10), and found that Be_<1-x>Mn_xTe is ferromagentic at the temperature lower than 10 K. Negative magnetoresistance and its hysterisis behavior were observed for the first time for Be_<1-x>Mn_xTe, which confirmed the carrierd-induced ferromagnetism. The observation of the Hall effect with the high magnetic field supported that the observed negative magnetoresistance is due to free carrier generation from bound magnetic polarons by the applied magnetic field.4. Luminescence properties of ZnSe/BeMnTe quatum well structuresWe investigated effects of applied electric and magnetic fields on luminescence properties, and found that the luminescence at the interfaces is enhanced and reduced by the applied-electric field. However, we could not observe a sharp luminescence band in the highly N-doped ZnSe/BeMnTe quantum well because of the interfacial roughness at the heterojunctions. Less