DISORDERED SUPERLATTICES

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A new semiconductor was proposed in 1989 which is featured by showing both the amorphous-like and the single-crystal-like properties. The proposed semiconducting materials are constructed either artificially or naturally so that chemical composition is disordered but physical alignment is sufficiently ordered for epitaxial growth to be possible. A disordered superlattice (d-SL) is an example of the proposed semiconductors. It was fabricated by changing individual layr widths disorderely in AlAs/GaAs superlattice. New optical and luminescence properties have been experimentally demonstrated in previous studies.In this study, the d-SLs of Al_xGa_<1-x>As/GaAs, AlAs/Al_yGa_<1-y>As, AlP/GaP,and Si_<1-x>Ge_x/Si were fabricated. The following new properties have been observed.(1) The luminescence intensity of the d-SL decays less with increasing temperature as compared with that of the ordered superlattice (o-SL) and the bulk alloy (b-AL) with the same chemical composition as the d-SL.The dis … More ordering effects were investigated with changing the Al composition, i.e., the energy band difference.(2) The effects depend proportionally on the band difference and thus become maximum at the AlAs/GaAs d-SL.(3) A good quality of the interface between AlP and GaP was obtained with using tertialybutylphosphine aand etching GaP substrate in (NH_4) S_x.(4) Photoluminescence (PL) intensities from the AlP/GaP d-SLs are 110-150 times stronger than those from the o-SLs and the b-AL at 9K.(5) PL intensities from the Si_<0.76>Ge_<0.24>/Si are several times stronger than those from the o-SLs and the b-AL at 10K.These results show that artificial disordering enhances effectively luminescent capability of the indirect-transition type of semiconductors such as AlP,GaP,Si, and Ge.The disordered effects were not satisfactorily created, since a large band difference cannot be taken due to the lattice mismatch. This would be improved with surfactan epitaxy. The d-SLs will be applied to luminescence devices in the further study. Less