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Previous Research : Wide Gap Nitride and II-VI Semimagnetic Superlattices |
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Introduction:The interband and intraband optical properties of wide band gap Nitride and II-VI heterostructures are studied at very high magnetic fields (60T): Interband magnetoreflectivity and magneto-PL is being used to study the complicated valence band structure of GaN based materials. Searches are being made for phonon polaron effects. The excitonic transitions of bulk CdMnTe are measured by reflectivity. In contrast to Gaj's paramagnetic model, the energy shift due to the sp-d exchange interaction continues to increase up to 45Tesla indicating the suppression of the antiferromagnetic interaction of Mn(2+) ions at high field. TypeI/TypeII transitions in semimagnetic semiconductors are extensively studied in two types of system in both Faraday and Voigt configurations by reflectivity and photoluminescence. In the CdTe/(Cd,Mn)Te system, by comparing the field-dependent energy shift of the heavy hole exciton from different concentration samples, indirect evidence for a type II exciton is observed. In the ZnTe/(Zn,Mn)Te system, a crossing of the 1s exciton transitions from the ZnTe buffer layer and the 1s heavy hole sigma+ exciton of the superlattice is observed, providing unambiguous evidence of a band alignment change from type I to type II. By applying a magnetic field perpendicular to the superlattice direction (Voigt configuration), s sudden drop in the photoluminescence is observed due to the competition between the Coulomb attraction and localisation by strong fields. Cyclotron resonance is performed on a series of CdTe/(Cd,Mg)Te modulation doped single quantum well to probe the electron-phonon interaction. The field dependent cyclotron masses increase slowly with magnetic field up to 30Tesla. This suggests that the resonant polaron effect in this measurement due to the high carrier density in the samples. |
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